KEK Theory Meeting on Particle Physics Phenomenology (KEK-PH2025winter)

18 Feb 2025, 09:00 → 21 Feb 2025, 20:00 Asia/Tokyo

The annual Theory Meeting on Particle Physics Phenomenology (KEK-­PH2025winter) will be held at KEK between Feb 18th -21th. This meeting covers many topics in Particle Physics and Cosmology, from the Standard Model and models beyond the Standard Model to particle cosmology and astrophysics. We plan to discuss recent developments in modeling Physics Beyond the Standard Model with their phenomenological aspects and also learn about the latest results and status of various ongoing and planned experiments. 

The meeting includes talks by invited speakers and short talks by participants. All the talks will be given in English. We aim to provide an opportunity, not only for experts but also for master/Ph.D course students, to learn recent developments in particle physics phenomenology and to activate intensive discussions.

Invited speakers

Motoko Fujiwara (U. of Toyama)
Christophe Grojean (DESY)
Koji Hashimoto (Kyoto U.)
Shigeki Hirose (U. of Tsukuba)
Shingo Kazama (Nagoya U.)
Akito Kusaka (U. Tokyo)
Zoltan Ligeti (LBNL)
Ian Low (Northwestern U./ANL)
Jacob Moritz (U. Wisconsin, Madison)
Takeo Moroi (U. Tokyo/KEK)
Kyohei Mukaida (KEK)
Abi Soffer (Tel Aviv U.)
Sokratis Trifinopoulos (MIT)
Jorinde van de Vis (CERN)
Wen Yin (Tokyo Metropolitan U.) 

Important dates

Deadline for workshop registration/KEK User registration/registration fee payment: February 4th (Tuesday)
For short talks and travel support applications: January 17th (Friday)
For those who need visa documents from KEK: January 5th (Sunday)

Registration fee: 3,500JPY (2,500JPY for students)

Tuesday, 18 February

10:00 → 10:10 opening

10:10 → 10:50 plenary: Christophe Grojean

10:10 TBA

Speaker: Christophe Grojean

10:50 → 11:10 coffee

11:10 → 11:50 plenary: Ian Low

11:10 TBA

Speaker: Ian Low

11:50 → 13:30 lunch break

13:30 → 14:50 plenary: Shigeki Hirose, Koji Hashimoto

13:30 TBA

Speaker: Shigeki Hirose

14:10 TBA

Speaker: Koji Hashimoto

14:50 → 15:20 coffee

15:20 → 16:20 parallel session A: flavor

15:20 Flavor anomalies and 2HDM with flavor symmetry

Anomalies in b -> s l l and b -> c l nu decays have persisted for over a decade. In this talk, I will explore the current landscape from three perspectives. First, global fits offer a model-independent approach to understanding the latest data. I will present our recent work on global fits incorporating around 200 binned observables, which reveals intriguing indications that new physics may manifest in the Wilson coefficient C9. Second, the Standard Model Effective Field Theory (SMEFT) provides a less model-dependent interpretation of experimental data and fitting outcomes. I will highlight several compelling predictions that emerge when data is analyzed through the SMEFT framework. Finally, the exploration and testing of specific new physics models remain crucial. I will introduce and examine a specific Two-Higgs-Doublet Model (2HDM) with gauge symmetry imposed on fermions, which accommodates anomalies in both neutral and charged currents.

Speaker: Fanrong Xu

15:40 The possible solution to V_cb puzzle from nontrivial analyticity of quark propagator

There is a longstanding tension between inclusive and exclusive |Vcb| determinations of Cabibbo-Kobayashi-Maskawa matrix element, i.e. Vcb puzzle. In this work, a nontrivial analytical structure of the quark propagator, indicated from the perspective of color confinement, is included for the first time in the inclusive B decay. To discuss the possibility of solving the Vcb puzzle, the observables B_d^0 lifetime and |Vcb| are analyzed. It is shown that the previous inclusive value based on operator product expansion is improved and thereby a possible resolution to the Vcb puzzle is given, which can be clarified with future determinations of parameters describing the complex conjugate poles.

Speaker: Jinglong Zhu

16:00 A novel approach to charm mixing

For $D^0-\bar{D}^0$ mixing, it is known that the operator product expansion cannot properly reproduce the order of magnitude of the experimental data. The difficulty in the conventional method arises from the significant cancellation due to the GIM mechanism. In this work, we analyze mass difference based on the Schwinger-Dyson approach. It is shown that the order of magnitude of the observable can be improved, compared to the conventional result.

Speaker: Hiroyuki Umeeda

15:20 → 16:20 parallel session B: theory

15:20 Evanescent contribution of the QCD theta angle

In this talk, we evaluate the QCD theta angle radiatively induced at the two-loop level using the dimensional regularization with the BMHV scheme in a simplified model. When the Lagrangian is promoted into d-dimensional space through the dimensional regularization, evanescent operators are introduced, which break the chiral symmetry. Consequently, a parity-odd fermion loop with the BMHV scheme generates an evanescent contribution that deviates from the original chiral symmetry. We carefully classify the evanescent contribution into two types: one originating from the evanescent operator and the other directly produced by the two-loop calculation. These unphysical contributions can be removed from the renormalization equation for the QCD theta angle by re-parameterizing the angle.

Speaker: Naohiro Osamura

15:40 Spontaneous CP violation in supersymmetric QCD

We investigate a composite model of spontaneous CP violation based on a new supersymmetric QCD as a solution to the strong CP problem. The scalar components of the meson chiral superfields obtain complex vacuum expectation values to break CP symmetry spontaneously. Then, wavefunction renormalization for the quark kinetic terms provides the Cabibbo-Kobayashi-Maskawa (CKM) phase, while the strong CP phase θ is protected by nonrenormalization of the superpotential and hermiticity of the wavefunction renormalization factor. In our model, the right-handed down-type quark multiplets are given by composite states, enhancing their couplings to CP breaking fields, which is essential to realize the observed CKM phase. The non-perturbative dynamics generates the scale of spontaneous CP violation hierarchically lower than the Planck scale. We discuss potential corrections to θ and find a viable parameter space of the model to solve the strong CP problem without fine-tuning.

Speaker: Yaoduo Wang

16:00 Does finetuning make D-term contributions smaller in natural grand unified theories with spontaneous supersymmetry breaking?

We explore the natural grand unified theory (GUT) with spontaneous supersymmetry
(SUSY) breaking, focusing on the contribution to sfermion and Higgs masses. Natural GUTs, which introduce all terms allowed by SO(10) × U (1)A symmetry with O(1) coefficients, provide a solution to the problems in SUSY GUTs. Although it is also possible to introduce spontaneous SUSY breaking, it predicts D-term contribution to sfermion and Higgs masses dominates the F-term contribution, that potentially leads to the SUSY flavor problem. Fortunately, it also predicts high-scale SUSY, which avoids the SUSY flavor problem but leads to the need for fine-tuning to obtain the electroweak scale and predicts superheavy Higgsino mass unless the D-term contribution becomes comparable with the F-term contribution. We discuss whether it is possible to suppress
the D-term contribution while maintaining the F-term contribution through the tuning of O(1) coefficients in the natural GUT with spontaneous SUSY breaking. Our results indicate that it is impossible. This also suggests that the Higgsino is not a candidate for dark matter in the scenario.

Speaker: Taiju Tanii

16:20 → 16:50 coffee

16:50 → 17:50 parallel session A: flavor

16:50 Analysis of Flavor Models by Diffusion Model

In conventional analyses of flavor models, the search space of parameters is often restricted to a certain range to optimize the parameters of the theory within a realistic computational time. In this talk, we propose an analytical method utilizing a diffusion model, which is a type of generative artificial intelligence. This strategy can be applied independently of the specific details of the models in contrast to the conventional methods. Through concrete examples, we will discuss how the predictions of flavor models can be evaluated from a bird's-eye view based on the inverse problem approach, where the machine generates various candidates of parameters that reproduce experimental values.

Speaker: Satsuki Nishimura

17:10 Heavy quark symmetry behind b → c semileptonic sum rule

Lepton flavor universality violations in semileptonic b→c transitions have garnered attention over a decade. For RH_c=BR(H_b→H_cτν)/BR(H_b→H_cℓν) with ℓ being e, μ, a sum rule among RD, RD∗ and RΛc was proposed to check consistency in the experimental results independently of new physics models. We revisit this relation from the perspective of the heavy quark symmetry. We derive a sum rule holding exactly in the heavy quark limit and clarify how model-dependent corrections are introduced in a realistic situation.

Speaker: Syuhei Iguro

17:30 Are Fractals Behind Flavor Mixing of the SM?

We explore the idea that the underlying flavour structure of the Standard Model could be determined by a fractal geometry. We consider theory space on a Sierpenski-like geometry. Fermion mass chains on Sierpinski-like geometry with three decorations(iterations) lead to three zero modes, which can be identified with three generations of the Standard Model. A single parameter expansion for each of the fermion mass matrices is achieved which explains the hierarchial masses as well as the mixing angles for the lepton sector. Extensions to the quark sector and related phenomenology are briefly discussed.

Speaker: Aadarsh Singh

16:50 → 17:50 parallel session B: theory

16:50 Gauge symmetry breaking with two dimensional sphere as extra dimensions

In the grand unified theory, the Higgs mechanism is commonly used. However, as an alternative approach, extra dimensions with non-zero curvature can lead to gauge symmetry breaking.

We have constructed a Yang-Mills theory with extra dimensions as two-dimensional sphere(S^2). As a result, the curvature of the extra dimensions and the non-commutative nature of the gauge group lead to a different gauge symmetry breaking process and origin of Higgs from conventional models such as those with S^1 and T^2.

In this talk, we report on the gauge symmetry breaking observed in the Kaluza-Klein expansion of four-dimensional gauge fields.

Speaker: Hiroki Ishikawa

17:10 Wiggly dilaton: a landscape of spontaneously broken scale invariance

The dilaton emerges as a pseudo-Nambu-Goldstone boson (pNGB) associated with the spontaneous breaking of scale invariance in a nearly conformal field theory (CFT). We show the existence of a wiggly dilaton potential that contains multiple vacuum solutions in a five-dimensional (5D) holographic formulation. The wiggly feature originates from boundary potentials of a 5D axion-like scalar field, whose naturally small bulk mass parameter corresponds to a marginally-relevant deformation of the dual CFT. Depending on the energy density of a boundary 3-brane, our model can be used to generate a light dilaton or provide a relaxion potential.

Speaker: Yu-Cheng Qiu

17:30 Mass spectrum of the extra-dimensional components of gauge fields in Yang-Mills theory with extra dimensions of two-dimensional sphere

The theoretical origin of the Higgs boson remains unclear. Yang-Mills theories in higher dimensions are good candidates to address this issue.
We have constructed a Yang-Mills theory with extra dimensions of two-dimensional sphere. In this model, compared to conventional models such as those with S^1 and T^2, curvature of the extra dimensions and the non-commutative nature of the gauge group result in different features in gauge symmetry breaking process and the origin of scalar fields.
In this talk, we will report the mass spectrum obtained from the Kaluza-Klein expansion of the gauge field components in the extra dimensions, which appear as scalar fields in our four-dimensional spacetime.

Speaker: Yuki Honda

17:50 → 18:00 break

18:00 → 20:00 reception

Wednesday, 19 February

09:00 → 10:20 plenary: Zoltan Ligeti, Abner Soffer

09:00 TBA

Speaker: Zoltan Ligeti

09:40 Recent updates and future prospects of the Belle II experiment

I will report recent results and prospects for future results from the Belle II experiment

Speaker: Abner Soffer

10:20 → 10:30 coffee

10:30 → 11:50 plenary: Sokratis Trifinopoulos, Shingo Kazama

10:30 Flavor Patterns of Fundamental Particles from Quantum Entanglement?

The Cabibbo-Kobayashi-Maskawa (CKM) matrix, which controls flavor mixing between the three generations of quark fermions, is a key input to the Standard Model of particle physics. In this paper, we identify a surprising connection between quantum entanglement and the degree of quark mixing. Focusing on a specific limit of 2→2 quark scattering mediated by electroweak bosons, we find that the quantum entanglement generated by scattering is minimized when the CKM matrix is almost (but not exactly) diagonal, in qualitative agreement with observation. With the discovery of neutrino masses and mixings, additional angles are needed to parametrize the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix in the lepton sector. Applying the same logic, we find that quantum entanglement is minimized when the PMNS matrix features two large angles and a smaller one, again in qualitative agreement with observation, plus a hint for suppressed CP violation. We speculate on the (unlikely but tantalizing) possibility that minimization of quantum entanglement might be a fundamental principle that determines particle physics input parameters.

Speaker: Sokratis Trifinopoulos

11:10 TBA

Speaker: Shingo Kazama

11:50 → 13:30 lunch break

13:30 → 14:30 parallel session A: collider

13:30 Single top plus Higgs production at the LHC

We study the single top plus Higgs production process at the LHC with a CP violating Yukawa coupling from a dimension-6 operator. The amplitude of the subprocess ub>dtH is obtained both in the Unitary (U) and Feynman-Diagram (FD) gauges. Energy and angular distributions of the cross section and CP violating asymmetries are understood from the interference among the FD gauge amplitudes.

Speaker: Yajuan Zheng

13:50 Transformers for jet tagging

Attention-based transformer models have become increasingly prevalent in collider analysis, offering enhanced performance for tasks such as jet tagging. However, they are computationally intensive and require substantial data for training. we introduce a new jet classification network using an MLP mixer, where two subsequent MLP operations serve to transform particle and feature tokens over the jet constituents. The transformed particles are combined with subjet information using multi-head cross-attention so that the network is invariant under the permutation of the jet constituents. The network structure is closely related to the multiscale nature of HEP events.
The proposed network demonstrates comparable classification performance to state-of-the-art models while boosting computational efficiency drastically. The network structure can be applied to the various collider processes.

Speaker: Ahmed Hammad

14:10 Dark photon pair production via off-shell dark Higgs at FASER

We consider a dark photon model in which the dark U(1) gauge symmetry is spontaneously broken by a vacuum expectation value of a new scalar boson. We focus on the ForwArd Search ExpeRiment (FASER) and calculate its sensitivity to the dark photon produced from the off-shell decay of the new scalar boson. It is found that the off-shell production extends the sensitivity region beyond the kinematical threshold of the on-shell decay of the scalar boson, and that the sensitivity region can be spanned to unexplored region. We also show the parameter space in which perturbative calculation is valid for the unitarity of an S matrix.

Speaker: Yohei Nakashima

13:30 → 14:30 parallel session B: dark matter

13:30 Photon Proliferation Effect from N-body ultralight DM annihilation

I will demonstrate a general photon proliferation effect from N-body ultralight dark matter (DM) annihilation in the early Universe, which can induce a drastic photon-temperature shift after neutrino decoupling. For pseudoscalar DM mass below the eV scale, I will show that the photon proliferation effect becomes significant as the mass approaches the ultralight end, presenting the leading constraints on the DM-photon coupling, DM self-interaction, and DM-electron coupling.

Speaker: Shaoping Li

13:50 Composite Dark Matter with Forbidden Annihilation

A dark matter model with QCD-like SU(N) gauge symmetry and electroweakly interacting dark quarks is discussed. In this model, the lightest G-parity odd dark pion is a main component of dark matter. I will discuss the relation between the mass spectrum of dark pions and annihilation channels which mainly contribute to the relic abundance. When the masses of dark matter and heavier dark pions are degenerate, dark matter mainly annihilates into the heavier dark pions and realizes heavy dark matter whose mass is O(1-10) TeV. I will also discuss the Sommerfeld effect of the annihilation channels.

Speaker: Takumu Yamanaka

14:10 pseudo-Nambu-Goldstone-boson as a Dark Matter Candidate: A Model with Three Complex Scalars under Z3 Symmetry

This study explores a dark matter model where the pseudo-Nambu-Goldstone boson (pNGB) emerges as a viable candidate, resulting from the spontaneous breaking of a U(1) symmetry and stabilized by a Z3 discrete symmetry which naturally emerges as a residual symmetry. The model introduces three complex scalar fields invariant under Standard Model (SM) gauge symmetries, naturally suppressing direct detection signals. We plan to investigate the thermal relic abundance, gauge kinetic mixing, and annihilation channels. Furthermore, we plan to examine boosted dark matter (semi-annihilation) channels, a feature of Z3​-symmetric models.

Speaker: Riasat Sheikh

14:30 → 15:00 coffee

15:00 → 16:00 parallel session A: collider

15:00 T violation at a future neutrino factory

We study the possibility of measuring T (time reversal) violation in a future long baseline neutrino oscillation experiment. By assuming a neutrino factory as a staging scenario of a muon collider at the J-PARC site, we find that the ν_e → ν_μ oscillation probabilities can be measured with a good accuracy at the Hyper-Kamiokande detector. By comparing with the probability of the time-reversal process, ν_μ → ν_e, measured at the T2K/T2HK experiments, one can determine the CP phase δ in the neutrino mixing matrix if | sin(δ)| is large enough. The determination of δ can be made with poor knowledge of the matter density of the earth as T violation is almost insensitive to the matter effects. The comparison of CP and T-violation measurements, `a la the CPT theorem, provides us with a non-trivial check of the three neutrino paradigm based on the quantum field theory.

Speaker: Sho Sugama

15:20 Higgs Boson Production at µ^+ µ^+ Colliders

Motivated by recent advancements in antimuon cooling, we study Higgs boson production at µ^+ µ^+ colliders at high energy. Since both initial-state particles are positively charged, there is no W boson fusion at the leading order, as it requires a W^+ W^− pair. However, we find that the cross section of the higher-order, γ- and Z-mediated W boson fusion process is large at high center-of-mass energies √s, growing as (log s)^3. This is in contrast to the (log s) behavior of the leading-order W boson fusion. Thus, even though it is a higher-order process, the rate of Higgs boson production for 10 TeV energies at µ^+ µ^+ colliders with polarized beams can be as high as about half of the one at µ^+ µ^− colliders, assuming the same integrated luminosity. To calculate the cross section of this process accurately, we carefully treat the collinear emission of the photon in the intermediate state. The thereby obtained large cross section furthermore shows the significance of Higgs production with an extra W boson in the final state also at µ^+ µ^− and e^+ e^− colliders.

Speaker: Lukas Treuer

15:40 Verifying the Resonance Schemes of Unstable Particles at Lepton Colliders

We propose practical ways of differentiating the various (Breit-Wigner, theoretical, and energy-dependent) resonance schemes of unstable particles at lepton colliders. First, the energy-dependent scheme can be distinguished from the other two by fitting the Z lineshape scan and forward-backward asymmetries at LEP and future lepton colliders with the Z mass mZ, decay width ΓZ, and coupling strength as fitting parameters. Although the Breit-Wigner and theoretical schemes work equally well, the scheme conversion requires the decay width ΓZ to scale inversely with mZ rather than the usual linear dependence from theoretical calculation. These contradicting behaviors can be used to distinguish the Breit-Wigner and theoretical schemes by the precision Z measurements with single parameter (mZ) fit at future lepton colliders. For the WW threshold scan, its combination with the precise Fermi constant provides another way of distinguishing the Breit-Wigner and theoretical schemes.

Speaker: Ui Min

15:00 → 16:00 parallel session B: dark matter

15:00 Excited bound states and their role in dark matter production

I explore the impact of highly excited bound states on the evolution of number densities of new physics particles, specifically dark matter, in the early Universe.

Higher excited states play a crucial role in non-Abelian interactions, going as far as preventing a complete decoupling in the early Universe and thus preventing the constituent particle from freezing out. Instead, a continuous depletion is driven by consecutive bound state formation and decay in the regime consistent with perturbativity and unitarity.

I will highlight how the mechanism has profound impact in a simplified dark matter model featuring a colored and electrically charged t-channel mediator. The focus is hereby on the regime of superWIMP production which is commonly characterized by a mediator freeze-out followed by its late decay into dark matter. In contrast, we find that excited states render mediator depletion efficient all the way until its decay, introducing a dependence of the dark matter density on the mediator lifetime as a novel feature. The impact of bound states on the viable dark matter mass can amount to an order of magnitude, relaxing constraints from Lyman-α observations.

Speaker: Stefan Lederer

15:20 Black String in the Standard Model

We found black string solutions in the 4 dimensional standard model, whose existence is suggested by swampland conjecture. The well-known no-go theorem for topologies of horizon except two sphere is avoided by taking into account the Casimir energy, which violate the dominant energy condition, in the energy-momentum tensor.

Speaker: Hayate Kimura

15:40 Realising Dark Matter and PTA via Dark Branes

In this work we propose a setup for the origin of dark matter based on spacetime with a warped extra dimension and three branes: the Planck brane, the TeV brane and a dark brane, at a (sub)-GeV scale. The Standard Model is localized in the TeV brane, thus solving the Higgs hierarchy problem, while the dark matter χ, a Dirac fermion, is localized in the dark brane. The dark matter has only gravitational interactions with the Standard Mode and we show that it can easily reproduce the thermal relic density by annihilations into radions and avoid direct detection experiments. The dark brane comes with a conformal sector confining at a 1st order phase transition generating a stochastic gravitational waves background which can accommodate the recent NANOGrav signal. A region in the parameter space of dark matter and radion masses is selected.

Speaker: Fotis Koutroulis

16:00 → 16:30 coffee

16:30 → 17:10 parallel session A: collider

16:30 Prospects for quantum process tomography at high energies

In quantum information theory, the evolution of an open quantum system -- a unitary evolution with the environment followed by a measurement -- is described by a Quantum Channel or, more generally, a Quantum Instrument. In this talk, I will formulate spin and flavour measurements in collider experiments as a Quantum Instrument. We demonstrate that the Choi matrix, which completely determines input-output transitions, can be both theoretically computed from a given theoretical model (e.g. the Standard Model) and experimentally reconstructed from a set of final state measurements (quantum state tomography) using varied input states. The reconstruction of the Choi matrix, known as quantum process tomography, offers a powerful new approach for probing potential extensions of the Standard Model within the QFT framework and also provides a fundamental test of Quantum Mechanics itself. As an example, I will outline a quantum process tomography approach applied to the e+ e- -> t tbar process at a polarized lepton collider.

Speaker: Kazuki Sakurai

16:50 New Physics Implications of Vector Boson Fusion Searches

LHC searches for nonstandard scalars in vector boson fusion (VBF) production processes can be particularly efficient in probing scalars belonging to triplet or higher multiplet representations of the Standard Model SU(2)L gauge group. They can be especially relevant for models where the additional scalars do not have any tree-level couplings to the Standard Model fermions, rendering VBF as their primary production mode at the LHC. In this work we employ the latest LHC data from VBF resonance searches to constrain the properties of nonstandard scalars, taking the Georgi-Machacek model as a prototypical example. We explicitly demonstrate how a combination of theoretical and phenomenological constraints can push the GM model toward the decoupling limit. Our analysis suggests that the VBF searches can provide key insights into the composition of the electroweak vacuum expectation value.

Speaker: Nivedita Ghosh

16:30 → 17:30 parallel session B: dark matter

16:30 Minimal dark matter in SU(5) grand unification

Minimal dark matter is an attractive candidate for dark matter because it is stabilized without the need to impose additional symmetries. It is known that the mass of the SU(2)L quintuplet fermion dark matter is predicted to be around 14 TeV, based on the thermal production mechanism. In this work, we embed the quintuplet dark matter within non-supersymmetric SU(5) grand unified theories. We find that two pairs of colored sextet fermions are required at the O (1-10) TeV scale to achieve gauge coupling unification, with the unification scale near the reduced Planck scale. These colored sextet fermions become metastable because their interactions are suppressed by the unification scale. Our model can be tested through comprehensive searches for colored sextet fermions in collider experiments, as well as through indirect and direct detection methods for minimal dark matter.

Speaker: Takashi Toma

16:50 Phenomenology of Neutrino-Dark Matter Interaction in DSNB and AGN

We introduce a neutrino-scalar dark matter (DM) ν-ϕ interaction and consider Diffuse Supernova Neutrino Background (DSNB) and Active Galactic Nuclei (AGN) representing distinctive neutrino sources. We focus on interaction mediated by a heavy fermionic particle F and investigate the attenuation of neutrino fluxes from these sources. We model the unscattered neutrino flux from DSNB via core-collapse supernova (CCSN) and star-formation rate (SFR), then use the DUNE experiment to set limits on DM-neutrino interaction. For AGNs, NGC 1068 and TXS 0506+056 where the neutrino carries energy above TeV, we select the kinematic region m^2_F ≫ E_ν m_ϕ ≫ m^2_ϕ such that the νϕ scattering cross section features an enhancement at high energy. We investigate the constraint on m_ϕ and scattering cross section by including DM density spikes at center of AGNs and computing the neutrino flux at IceCube, where the ϕϕ∗ annihilation cross section is implemented to obtain the saturation density of the spikes.

Speaker: Po-Yen Tseng

17:10 Composite asymmetric dark matter with a dark photon portal: Multi-Messenger tests

Composite asymmetric dark matter (ADM) is the framework that naturally explains the coincidence of the baryon density and the dark matter density of the Universe. Through a portal interaction sharing particle-antiparticle asymmetries in the Standard Model and dark sectors, dark matter particles, which are dark-sector counterparts of baryons, can decay into antineutrinos and dark-sector counterparts of mesons (dark mesons) or dark photon. Subsequent cascade decay of the dark mesons and the dark photon can also provide electromagnetic fluxes at late times of the Universe. We derive constraints on the lifetime of dark matter decay in the composite ADM scenario from the astrophysical observations of the e+, e-, and γ-ray fluxes. The constraints from cosmic-ray positron measurements by AMS-02 are the most stringent at ≳2 GeV: a lifetime should be larger than the order of 1026 s, corresponding to the cutoff scale of the portal interaction of about 108 -- 109 GeV. We also show the importance of neutrino observations with Super-Kamiokande and Hyper-Kamiokande, which give conservative bounds.

Speaker: Takumi Kuwahara

Thursday, 20 February

09:00 → 10:20 plenary: Takeo Moroi, Motoko Fujiwara

09:00 Dark Matter Detection using Quantum Bits

I will discuss a possibility to use quantum bits (qubits) for wave-like-dark-matter detection. I will explain the basic idea and show the expected sensitivity. I will also discuss an idea to enhance the sensitivity using quantum nature of the qubits.

Speaker: Takeo Moroi

09:40 Particle Dark Matter: A Bird's-Eye View of Recent Progress

Dark matter is a subject of active research across many disciplines. In particle physics, efforts are ongoing to expand the range of theoretical scenarios and refine predictions motivated by upcoming observations. Recently, cross-disciplinary approaches have been increasingly studied, integrating insights from atomic nuclei, astrophysics, and other fields to propose novel search directions. In this talk, I will provide an overview of these recent developments.

Speaker: Motoko Fujiwara

10:20 → 10:30 coffee

10:30 → 11:50 plenary: Wen Yin, Akito Kusaka

10:30 Undulators as axion factories

I will present a low-cost experimental proposal for axion searches at synchrotron radiation facilities, such as SPring-8, NanoTerasu, and Photon Factory. Specifically, I will discuss the method for calculating axion production in an undulator, a type of light source widely used across various fields. By positioning an axion detector outside the shield used in the primary experiments, we can conduct a sustainable, coexisting axion search experiment. This approach has the potential to set a world record in the light-shining-through-a-wall experiment for probing the heavy axion mass range.

Speaker: Wen Yin

11:10 TBA

Speaker: Akito Kusaka

11:50 → 13:30 lunch break

13:30 → 14:30 parallel session A: dark matter / baryogenesis

13:30 Sterile neutrino dark matter production in lepton asymmetric universe and its observational implications

Sterile neutrino with masses of the keV scale is a fascinating candidate for dark matter. In particular, in the presence of significant lepton asymmetry in the standard model neutrino sector in the early universe, resonantly produced sterile neutrinos can explain all dark matter consistent with all the observational constraints. Such a large lepton asymmetry has also been suggested by recent observation of the Helium-4 abundance in the metal-poor galaxies. In this talk, we revisit the comprehensive analysis of the allowed parameter region for the resonant production scenario of sterile neutrino DM. Furthermore, we also show that such a significant lepton asymmetry can be realized within the framework of Affleck-Dine leptogenesis, which is based on minimal supersymmetric standard model. In our setup, the AD scalar with leptonic charge forms a non-topological solitons (Q-balls) that eventually dominate the energy density of the universe before decaying into a lepton-asymmetric thermal plasma.
Since the Q-ball decay process is sufficiently instantaneous, scalar-induced GWs is significantly enhanced at the sudden decay of Q-balls. In the last part of the presentation, we show the improved estimate of the GWs at such a sudden transition from Q-ball dominated era to radiation-dominated era.
This presentation is based on arXiv:2402.11902.

Speaker: Kentaro Kasai

13:50 DM relic abundance via multi-Higgs production in the early universe

It is widely believed that parameter space for Higgs-portal dark matter which achieves the relic abundance through the thermal freeze-out is already tightly constrained. In this talk, we propose a novel scenario that the multiple Higgs production dramatically change this picture. As a result, the relic abundance of DM can be achieved by heavy Higgs-portal DM of $m_\chi\gtrsim{\cal O}(1)$ TeV in the same way with those for usually considered weakly interacting massive particle models.

Speaker: Seishi Enomoto

14:10 New EDM bounds for electroweak baryogenesis with the minimal setup for CP violation in the extended Higgs model

Electroweak baryogenesis is a promising baryogenesis scenario, which can be tested in various future experiments.
In the mechanism of electroweak baryogenesis, new sources of the CP violation are needed to generate the baryon asymmetry of the Universe.
This new CP violation can be explored in the current and future electric dipole moment (EDM) experiments.
In this talk, we classify the CP violation in the extended Higgs models and find a crucial CP phase for electroweak baryogenesis.
We discuss baryogenesis by this phase and show the unavoidable bounds on the EDMs, which would be reached in future experiments.

Speaker: Yushi Mura

13:30 → 14:30 parallel session B: pheno

13:30 Lepton Flavor Violating Decay of True Muonium

Lepton Flavor Violation (LFV) serves as a crucial probe into physics beyond the Standard Model. To identify the new particles behind LFV, it is important to search for various types of LFV processes, because the LFV mediators indirectly appear in most of LFV processes.
In this study, we propose a new LFV process, the decay of a muon-antimuon bound state into an electron-antimuon (or positron-muon) pair. We calculate the decay rate with scalar-, vector-, and dipole-type operators. Furthermore, we evaluate the discovery potential in future experiments by comparing the results with existing experimental constraints.

Speaker: Ryotaro Minato

13:50 Axion detection with quantum Hall effect

A detailed examination of the plateau transition in the quantum Hall effect reveals the presence of axion influence. In quantum Hall effect experiments, strong magnetic fields are used, and microwaves generated by axions from the surrounding metallic walls are emitted. These microwaves are absorbed by localized electrons, causing them to transition to a delocalized state and contribute to the current. This effect impacts the Hall conductivity. When the Fermi energy is in the localized state of electrons, the Hall conductivity remains constant, forming a plateau. However, when the electrons are in the delocalized state, the Hall conductivity changes, leading to a plateau transition. The presence of axion-induced microwaves affects this plateau transition. Therefore, by carefully re-examining the plateau transition, we can observe the axion’s influence and demonstrate that its mass is 10^{-5} eV

Speaker: Aiichi Iwazaki

14:10 High frequency gravitons from inflation

We show that gravitons are efficiently produced through various processes during reheating. The detection of ultra high frequency stochastic gravitational waves can directly determine the inflaton mass, decay rate etc.

Speaker: Kazunori Nakayama

14:30 → 15:00 coffee

15:00 → 16:00 parallel session A: leptogenesis

15:00 A new mechanism for leptogenesis in three-Higgs-doublet models

In standard leptogenesis, several conditions must be satisfied to produce the observed baryon asymmetry: weak wash-out, CP violation in the neutrino Yukawa couplings, and a heavy Majorana mass.
We propose a new mechanism for leptogenesis that relaxes these conditions by employing three-Higgs-doublet models. The non-thermal decay of an additional heavy Higgs generates a charge asymmetry, which remains conserved in the early universe. This asymmetry is subsequently converted into a lepton asymmetry through thermal processes involving neutrino Yukawa interactions.
Our results indicate that the Majorana mass scale can be reduced to as low as 10^5GeV.

Speaker: Hidenaga Watanabe

15:20 Leptogenesis and Neutrinoless Double-Beta Decay

We revisit the thermal leptogenesis based on the Type I seesaw mechanism and discuss the constraints from future neutrino experiments. Taking the flavor effects into account, we study the influence of the Majorana phases and the effective neutrino Majorana mass for neutrinoless double-beta decay. We present the lower bounds of the right-handed neutrino mass on a plane consisting of the lightest neutrino mass and the effective neutrino Majorana mass.

Speaker: Tatsuya Yokoyama

15:40 Leptogenesis in the presence of density perturbations

I point out a new effect on the freeze-out process of heavy particles induced by density perturbations in the early universe.
Already at moderately large density perturbations $\delta T / \bar{T} \sim 10^{-2}$, this effect cannot be captured by linear perturbation theory.
I illustrate this effect with leptogenesis and discuss phenomenological implications.
I consider the simplest case of leptogenesis
and include only the decays and inverse decays of heavy neutrinos
in the presence of density perturbations.
As a result, I found that perturbations change
the freeze-out values of the lepton asymmetry,
and increase the spatial average of the asymmetry.
Furthermore, constraints on the mass of heavy neutrinos
become relaxed in the presence of perturbations
compared to the case without perturbations,
which is due to a beyond-linear effect caused by the
exponential decoupling of heavy neutrinos from the thermal bath.

Speaker: Rin Takada

15:00 → 16:00 parallel session B: pheno

15:00 Impact of the Electroweak Weinberg Operator on the Electric Dipole Moment of Electron

The electric dipole moments (EDM) of electron, an observable sensitive to CP violation, is expected to plobe physics beyond the Standard Model (BSM) at TeV scale due to significant improvements in experimental precision. In this study, we evaluated the CP-violating dimension-6 operator for electroweak bosons (the electroweak Weinberg operator) generated at the two-loop level by CP-violating Yukawa interactions involving BSM fermions and scalars in a form independent of scalar particles. We calculated the contribution of this operator to the electron EDM. when the scalar is a BSM scalar,this contribution represents a new 3-loop effect. In contrast, when the scalar is the SM Higgs, this contribution becomes a higher order correction to the 2-loop contribution of the Barr-Zee diagram. We examined the significance of this contribution and suggest that the 3-loop contributions to the electron EDM from BSM models could be tested in future experiments. We examined the significance of this contribution and suggest that the 3-loop contributions to the electron EDM induced by BSM models, such as the dark matter model with electroweak interacting massive fermions, could be tested in future experiments.

Speaker: Kiyoto Ogawa

15:20 Constraints on Trilinear Higgs Couplings Including One-loop Correction in Nearly Aligned Higgs Models

Although the Higgs boson has been discovered, the couplings between the Higgs boson and Standard Model (SM) particles may deviate from the predictions of the SM. Such deviations can be realized by extending the SM. One possible extension involves the introduction of an extended Higgs model, which extends the Higgs sector. Among extended Higgs models, the nearly aligned Higgs model, characterized by a single classical field, features a Higgs potential whose shape varies depending on the specific model. Classifying models based on the shape of their Higgs potentials provides an effective method for scrutinizing multiple models through high-precision measurements of the trilinear Higgs coupling.
In this study, we calculate the trilinear Higgs coupling, including one-loop corrections from the top quark and new particles, for several representative models. The parameters of these models, derived from the trilinear Higgs couplings, are constrained by expected measurements such as the High-Luminosity LHC and the International Linear Collider. This presentation reports on results from work in progress.

Speaker: Shuhei Ohzawa

15:40 New Constraints on Gauged U(1)Lμ-Lτ Models via Z-Z' Mixing

Models based on a U(1)$_{L_\mu-L_\tau}$ gauge symmetry can explain the discrepancy between the measured value and theoretical prediction of the muon anomalous magnetic moment. Based on the latest experimental results, we revisit the analysis of neutrino mass matrix structures in minimal U(1)$_{L_\mu-L_\tau}$ models where the U(1)$_{L_\mu-L_\tau}$ symmetry breaking is caused by a single scalar field. Due to the charge assignment of the scalar field, each model predicts a unique structure of the neutrino mass matrix, which demands non-trivial relations among neutrino mass and mixing parameters. We find that the model called type ${\bf 2}_{+1}$, which features an SU(2)$_L$ doublet scalar $\Phi_{+1}$ with the U(1)$_{L_\mu - L_\tau}$ charge $+1$ and the hypercharge $+1/2$ and predicts the $\bf B_3$ texture structure, is marginally acceptable under the current neutrino oscillation data and cosmological observation. When the U(1)$_{L_\mu - L_\tau}$ gauge symmetry is broken by the vacuum expectation value of the standard model non-singlet representation such as $\Phi_{+1}$, there are additional contributions to flavor-changing meson decay processes and atomic parity violation via mixing between the $Z$ boson and the U(1)$_{L_\mu-L_\tau}$ gauge boson $Z'$. We newly evaluate the model-dependent constraints on the model and find that the type ${\bf 2}_{+1}$ model is robustly ruled out. The model is extended to have an additional vacuum expectation value of a standard model singlet scalar in order to avoid the stringent constraints via the $Z-Z'$ mixing. Finally, we clarify the allowed range of the ratio of these vacuum expectation values.

Speaker: Coh Miyao

16:00 → 16:30 coffee

16:30 → 17:30 parallel session A: leptogenesis

16:30 Flavored leptogenesis in Scotogenic models

Flavor effect in leptogenesis is an important effect that can potentially change the baryon asymmetry by up to an order of magnitude.
The scotogenic model proposed by Ernest Ma is an attractive and minimally extended model for producing small neutrino masses through radiative corrections in the dark matter sector.
It is also known that the scotogenic model can explain the baryon asymmetry of the Universe via low-scale leptogenesis.
In this research, We calculated the baryon asymmetry in scotogenic model taking into consideration flavor effect.

Speaker: Yurika Sekikawa

16:50 Thermal leptogenesis in SO(10)×U(1) GUT

In this study, we show that thermal leptogenesis is successful in the natural SO(10) GUT.
When lepton flavor effects are added to thermal leptogenesis, the second-lightest right-handed neutrino contribute non-negligibly. Compared to the mass of the right-handed neutrino predicted by the symmetry of the natural SO(10) GUT, that obtained in this study is about six times smaller than that of the lightest right-handed neutrino contribution. Furthermore, the mass of the left-handed neutrino, determined by the same symmetry, is also predicted to be about 1/6.

Speaker: Kei Shibata

17:10 The time evolution of lepton numbers, Majorana (type) phases and the connection to CP violation for leptogenesis

The time evolution of lepton numbers of Majorana neutrinos are sensitive to neutrino masses , the mixing angles , and CP violation at low energy including Majorana phases and Dirac Kobayashi Maskawa type phase. This implies one can theoretically reconstruct all the elements of the effective Majorana mass matrix at low energy using the time evolution of lepton numbers. In this talk, we diagonalize the 2 × 2　effective Majorana matrix for two generations of the active Majorana neutrinos and express a Majorana phase, the two neutrinos masses, and a mixing angle in terms of the elements of the mass matrix. Then by assuming the origin of the effective Majorana mass matrix comes from type I seesaw model with two gauge singlet neutrinos, we have derived the relation of the single Majorana phase at low energy and two CP violating phases relevant for leptogenesis by drawing the triangles for the elements of the mass matrix in the complex plane which shows the contribution of each singlet neutrino to the elements of the effective Majorana mass matrix.
The talk is based on arXiv:2212.00142v4[hep-ph] 27 Dec 2024.
Nicholas J. Benoit, Yuta Kawamura, Saki Hamada, Takuya Morozumi, Yusuke Shimizu, Kei Yamamoto

Speaker: Takuya Morozumi

16:30 → 17:10 parallel session B: pheno

16:30 Effective field theory for type II seesaw model --symmetric phase v.s. broken phase--

Effective field theory is an effective approach to parameterizing effects of high energy scale physics in low energy measurements. The two popular frameworks for physics beyond the standard model are the so-called Standard Model Effective Field Theory (SMEFT) and the Higgs Effective Field Theory (HEFT). While the description by the SMEFT deteriorates when the new physics scale is not so high or it participates in spontaneous electroweak symmetry breaking, the HEFT makes use of nonlinear realization of spontaneously broken symmetry in which there are practically no restrictions on the Higgs field as a singlet. In this work we present another framework, called broken phase effective field theory (bEFT), in which we deal directly with mass eigenstate fields after spontaneous symmetry breaking without employing nonlinear realization. We take the type-II seesaw model as an example to demonstrate our approach. By matching the model at tree level to both bEFT and SMEFT, we compare the results for two processes, the Higgs pair production via vector boson fusion at the LHC and the Higgs-strahlung process at the International Linear Collider. We find that the bEFT reproduces the type-II seesaw model more accurately than the SMEFT in the regions where the bare mass of the Higgs triplet becomes close to the electroweak scale.

Speaker: Yoshiki Uchida

16:50 The probability for chiral oscillation of Majorana neutrino in Quantum Field Theory

We derive the probability for chiral oscillation of Majorana neutrinos based on quantum field theory. Since the Hamiltonian under the Majorana mass term does not conserve lepton number, the eigenstates of lepton number change continuously over time. Therefore, the transition amplitude is described by the inner product of the eigenstates of lepton number at the time of the neutrino production and the detection. With the Bogoliubov transformation, we successfully relates the lepton number eigenstates at different times. This method enables us to understand the time variation of lepton number induced by chiral oscillations in terms of transition probabilities. We also present the physical picture that emerges through the Bogoliubov transformation.

Speaker: Tomoharu Tahara

Friday, 21 February

09:00 → 09:40 plenary: Jacob Moritz

09:00 TBA

Speaker: Jacob Moritz

09:40 → 09:50 coffee

09:50 → 10:50 parallel session A: cosmo

09:50 Effects of electroweak phase transition on dark matter relic abundance

The true identity of dark matter (DM) is an unsolved problem in physics. Among the various DM candidates, weakly interacting massive particles (WIMP) are attractive because their abundance can be explained thermally. The WIMP abundance can be estimated using the Boltzmann equation, and particle masses at zero temperature are usually adopted. In this study, we take into account the electroweak phase transition, i.e., the particle masses should change with temperature through a varying vacuum expectation value of Higgs. We compare the DM abundance obtained using the conventional calculation method with our results using the temperature-dependent particle masses.

Speaker: Chikako Idegawa

10:10 Completing the perturbative program for cosmological phase transitions

Scale hierarchies are required to reliably describe the thermodynamics of cosmological first-order phase transitions using perturbation theory. At finite temperature, such a hierarchy is provided naturally. One can then use this hierarchy to construct a three-dimensional effective field theory (EFT) that systematically includes thermal resummations to all orders.

Using this EFT setup, I discuss completing the perturbative program for equilibrium thermodynamics of cosmological first-order phase transitions by determining the finite-temperature effective potential of gauge-Higgs theories at next-to-next-to-next-to-next-to-leading order (N4LO) [1,2]. This N4LO result is the last perturbative order before confinement renders electroweak gauge-Higgs theories non-perturbative at four-loops. In contrast with non-perturbative lattice results, the perturbative thermodynamic predictions show remarkable agreement. As a direct application for predictions of gravitational waves produced by a first-order transition, this computation provides the final fully perturbative results for the phase transition strength and speed of sound.

[1] A. Ekstedt, P. Schicho, and T. V. I. Tenkanen, DRalgo: A package for effective field theory approach for thermal phase transitions, Comput. Phys. Commun. 288, 108725 (2023), [2205.08815].
[2] A. Ekstedt, P. Schicho, and T. V. I. Tenkanen, Cosmological phase transitions at three loops: The final verdict on perturbation theory, Phys. Rev. D 110, 096006 (2024), [2405.18349].

Speaker: Philipp Schicho

10:30 Reheating Process after Axion Inflation

In modern cosmology, it is generally assumed that after inflation, the energy of the inflaton is transferred to radiation through a process known as reheating. Axion-like particles (ALPs) have recently emerged as compelling candidates for the inflaton, primarily because their approximate shift symmetry helps preserve the flatness of the inflationary potential.

This study investigates the reheating process within a model where ALPs are coupled to non-Abelian gauge fields via Chern-Simons interactions. As established in preheating analyses, energy transfer occurs resonantly in this scenario, leading to efficient energy conversion. However, any residual inflaton remaining in the universe could potentially re-dominate the energy density over time.

In this talk, I will present how reheating could be completed in this context and discuss its possible implications for the early universe’s evolution.

Speaker: Tenta Tsuji

09:50 → 10:50 parallel session B: axion

09:50 QCD axion from chiral gauge theories

We present models of axion based on supersymmetric chiral gauge theories. In these models, the PQ symmetry is spontaneously broken by the non-perturbative dynamics of chiral gauge theory. Thanks to supersymmetry, IR dynamics of the models are calculable. We also present an example of a QCD axion model that is compatible with SU(5) grand unification. To avoid the proton decay constraint and a Landau pole of gauge coupling below the Planck scale, the PQ breaking scale is higher than the GUT scale.

Speaker: Shonosuke Takeshita

10:10 How viable is a QCD axion near 10 MeV?

There has been an attempt to revive the visible QCD axion at the 10 MeV scale
assuming that it exclusively couples to the first-generation quarks and the electron.
This variant of the QCD axion is claimed to remain phenomenologically viable,
partly due to a clever model construction that induces tree-level pion-phobia and exploits uncertainties inherent in the chiral perturbation theory.
We confront this model with the cosmological domain wall problem, the quality issue
and constraints arising from the electron electric dipole moment.
It is also pointed out that the gluon loop-generated axion-top coupling can provide a very large contribution to rare $B$-meson decays, such that the present LHCb data for $B^0 \to K^{*0} e^+ e^-$ rule out the model for the axion mass larger than 30 MeV.
There is a strong motivation for pushing the experimental analysis of $B \to K^{(*)} e^+ e^-$ to a lower $e^+ e^-$ invariant mass window, which will conclusively determine the fate of the model, as its contribution to this branching ratio significantly exceeds the Standard Model prediction.

Speaker: Junxuan Xu

10:30 High Quality QCD axion via Electric-Magnetic Duality

Axion can solve the strong CP problem dynamically. However, since a global symmetry is expected to be broken explicitly in quantum gravity theory, any extra Peccei-Quinn (PQ) symmetry breaking operator must be suppressed, except for nonperturbative effects of QCD. In this talk, we propose a novel paradigm for the QCD axion with high-quality PQ symmetry on the basis of electric-magnetic duality in the conformal window of a supersymmetric gauge theory. PQ breaking fields emerge in the magnetic theory and possess a large anomalous dimension, which leads to not only generation of an intermediate scale of spontaneous PQ breaking but also significant suppression of explicit PQ symmetry breaking operators. The high PQ quality and the absence of a Landau pole in the color gauge coupling are achieved. We will also show the parameter space to realize the correct abundance of the axion dark matter.

Speaker: Shota Nakagawa

10:50 → 11:00 coffee

11:00 → 12:20 plenary: Kyohei Mukaida, Jorinde van de Vis

11:00 TBA

Speaker: Kyohei Mukaida

11:40 The bubble wall velocity in cosmological phase transitions

Cosmological first order phase transitions are a promising source of gravitational waves, and a possible explanation of the baryon asymmetry and dark matter abundance.
Predicting the phenomenological consequences of such phase transitions requires knowledge of the expansion velocity of the bubbles formed in a phase transition.
In this talk, I will present WallGo, a software package for the computation of bubble wall velocities. WallGo is the first publicly available code that computes the matrix elements, collision integrals Boltzmann equation and scalar field equation of motion for user-defined models. I will present results obtained with WallGo, and discuss its limitations.
Lastly, I will discuss several simplifying regimes in the computation of the wall velocity, such as the ballistic limit and a large jump in degrees of freedom.

Speaker: Jorinde van de Vis

12:20 → 13:00 closing