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

Session

parallel session A

Feb 18, 2025, 3:20 PM

seminar hall (Building 3)

Conveners

parallel session A: flavor

• Takuya Morozumi

parallel session A: flavor

• Takuya Morozumi

parallel session A: collider

• Mihoko Nojiri

parallel session A: collider

• Mihoko Nojiri

parallel session A: collider

• Mihiko Nojiri

parallel session A: dark matter / baryogenesis

• Motoko Fujiwara

parallel session A: leptogenesis

• Motoko Fujiwara

parallel session A: leptogenesis

• Motoko Fujiwara

parallel session A: cosmo

• Yuta Hamada

19. Flavor anomalies and 2HDM with flavor symmetry

Fanrong Xu

2/18/25, 3:20 PM

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...

20. The possible solution to V_cb puzzle from nontrivial analyticity of quark propagator

Jinglong Zhu

2/18/25, 3:40 PM

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...

21. A novel approach to charm mixing

Hiroyuki Umeeda

2/18/25, 4:00 PM

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...

22. Analysis of Flavor Models by Diffusion Model

Satsuki Nishimura

2/18/25, 4:50 PM

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...

23. Heavy quark symmetry behind b → c semileptonic sum rule

Syuhei Iguro

2/18/25, 5:10 PM

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...

31. Single top plus Higgs production at the LHC

Yajuan Zheng

2/19/25, 1:30 PM

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.

32. Transformers for jet tagging

Ahmed Hammad

2/19/25, 1:50 PM

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...

33. Dark photon pair production via off-shell dark Higgs at FASER

Yohei Nakashima

2/19/25, 2:10 PM

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...

34. T violation at a future neutrino factory

Sho Sugama

2/19/25, 3:00 PM

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...

35. Higgs Boson Production at µ^+ µ^+ Colliders

Lukas Treuer

2/19/25, 3:20 PM

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...

36. Verifying the Resonance Schemes of Unstable Particles at Lepton Colliders

Ui Min

2/19/25, 3:40 PM

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...

37. Prospects for quantum process tomography at high energies

Kazuki Sakurai

2/19/25, 4:30 PM

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...

38. New Physics Implications of Vector Boson Fusion Searches

Nivedita Ghosh

2/19/25, 4:50 PM

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...

24. Are Fractals Behind Flavor Mixing of the SM?

Aadarsh Singh

2/19/25, 5:10 PM

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...

48. Sterile neutrino dark matter production in lepton asymmetric universe and its observational implications

Kentaro Kasai

2/20/25, 1:30 PM

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...

50. New EDM bounds for electroweak baryogenesis with the minimal setup for CP violation in the extended Higgs model

Yushi Mura

2/20/25, 1:50 PM

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...

72. Memory-Burdened Primordial-Black-Hole Dark Matter probed by Induced Gravitational Waves

Takahiro Terada

2/20/25, 2:10 PM

Quantum evaporation of a black hole is conventionally studied semiclassically by assuming self-similarity of the black hole throughout the evaporation process. However, its validity was recently questioned, and the lifetime of a black hole is conjectured to be much extended by the memory burden effect. It gives rise to the possibility that the primordial black holes (PBHs) lighter than 10^10...

51. A new mechanism for leptogenesis in three-Higgs-doublet models

Hidenaga Watanabe

2/20/25, 3:00 PM

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...

52. Leptogenesis and Neutrinoless Double-Beta Decay

Tatsuya Yokoyama

2/20/25, 3:20 PM

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...

53. Leptogenesis in the presence of density perturbations

Rin Takada

2/20/25, 3:40 PM

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...

54. Flavored leptogenesis in Scotogenic models

Yurika Sekikawa

2/20/25, 4:30 PM

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...

55. Thermal leptogenesis in SO(10)×U(1) GUT

Kei Shibata

2/20/25, 4:50 PM

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...

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

Takuya Morozumi

2/20/25, 5:10 PM

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...

65. Effects of electroweak phase transition on dark matter relic abundance

Chikako Idegawa

2/21/25, 9:50 AM

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...

66. Completing the perturbative program for cosmological phase transitions

Philipp Schicho

2/21/25, 10:10 AM

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...

67. Reheating Process after Axion Inflation

Tenta Tsuji

2/21/25, 10:30 AM

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...

49. DM relic abundance via multi-Higgs production in the early universe

Seishi Enomoto

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...