Neutron Stars and Quark-Hadron Continuity (Motoi Tachibana)

Neutron star is a stellar remnant after supernova explosion. Since its density is so high, exotic matter states, such as superfluid neutrons, Bose-Einstein condensate of mesons, superconducting quarks (and even dark matter), are expected to be present inside of it. In this talk, I will focus on a concept "quark-hadron continuity", originally proposed by Schafer and Wilczek and construct a concrete model to realize it. Then I will apply the idea into physics of neutron stars, such as vortex formation and mass-radius relation.

Renormalization group improvement for thermally resummed effective potential (Koichi Funakubo)

To improve the perturbative calculations of the effective potential used in the study of phase transitions in the early universe, the resummation of the thermal masses is often employed. In conventional perturbation theory, the improvement using the renormalization group have benn well known, but the application of the renormalization group in the presence of resummation had not been well understood. We developed a new renormalization group method by interpreting resummation as a form of finite renormalization and demonstrated improvements in perturbation theory using a simple scalar theory. In this talk, I will present the construction of a renormalization scale-invariant effective potential and introduce a method to improve perturbation theory by utilizing scale invariance.

Excited bound states and their role in dark matter production (Stefan Lederer)

I will discuss the impact of highly excited bound states on the evolution of number densities of new physics particles, focusing on dark matter, in the early Universe.  In case of non-Abelian gauge interactions, which source dipole interactions between fundamental particles, highly excited states can prevent the particles from freezing, supporting a continuous depletion in the regime consistent with perturbativity and unitarity. Unitarity violation does in fact arise systematically, that is even for arbitrary small interaction strengths, once sufficiently highly excited states become relevant at low velocities. Novel analytic expressions for bound state formation, which we found recently, allow to accurately compute the freeze-out dynamics down to very low temperatures.  I will highlight the importance of bound states to dark SU(N) sectors. For a more concrete dark matter model, I will focus on a colored and charged t-channel mediator model in the regime of superWIMP production. Here, excited states render the 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. [arXiv: 2308.01336, 2411.08737]

An extended Higgs model for neutrino mass, dark matter, and baryon asymmetry (Sora Taniguchi)

Aoki-Kanemura-Seto model (AKS model) is a new physics model that can explain neutrino mass, dark matter and baryon asymmetry of the universe, but the baryon number has not yet been evaluated in the original model. The CP-violating phase in the Higgs potential is important to explain the observed baryon asymmetry in the electroweak baryogenesis scenario. However, such a phase is severely constrained by the measurements of the electron electric dipole moment (EDM) . In this talk, we show that the electron EDM can be suppressed by interference between the phase in the Higgs sector and the dark sector. We discuss the possibility of explaining three phenomena.

Probing BSM effects for realizing first-order phase transition (Katsuya Hashino)

In the standard model (SM), the electroweak phase transition (EWPT) is crossover. When new physics effects beyond the SM modify the Higgs potential, the EWPT can become a first-order phase transition. Such a phase transition in the early Universe could produce gravitational waves (GWs) and primordial black holes (PBHs). Since the GW spectra and PBH abundance depend on the shape of Higgs potential, we can use their observations to probe beyond the SM effects for first-order phase transition. In this talk, we consider the Higgs potential which can realize the first-order phase transition, and discuss the testability of new physics effects via the GW and PBH observations.

Current status of B anomalies (Satoshi Mishima)

Semi-leptonic B-meson decays have attracted significant attention over the past decade due to persistent discrepancies between experimental data and Standard Model predictions, commonly referred to as "B anomalies." In this talk, I will first review the current status of these decays and discuss possible new physics scenarios that could account for the anomalies. In the second part of the talk, I will focus on a sum rule that approximately holds for b → cτν semi-leptonic decays. The sum rule was empirically found a few years ago, and we have recently demonstrated that an exact version of the sum rule can be derived in the heavy quark limit. I will present our findings and discuss how the sum rule is modified in more realistic scenarios beyond the heavy quark limit.

Impact of the Electroweak Weinberg Operator on the Electric Dipole Moment of Electron (Naohiro Osamura)

Recent progress in the electric dipole moment (EDM) measurements of the electron using the paramagnetic atom or molecule is remarkable. In this paper, we calculate a contribution to the electron EDM at three-loop level, introducing the CP-violating Yukawa couplings of new SU(2)$_L$ multiplets. At two-loop level, the Yukawa interactions generate a CP-violating dimension-six operator, composed of three SU(2)$_L$ field strengths, called the electroweak-Weinberg operator. Another one-loop diagram with this operator inserted induces the electron EDM. We derive the matching condition and find that even if new SU(2)$_L$ particles have masses around the TeV scale, the electron EDM may be larger than the Standard Model (SM) contribution to the paramagnetic atom or molecule EDMs. We also discuss the relation between the Barr-Zee diagram contribution at two-loop level and three-loop one, assuming that the SM Higgs has new Yukawa interactions with the SU(2)$_L$ multiplets.

Novel loop-diagrammatic approach to QCD theta parameter (Naohiro Osamura)

When the QCD axion is absent in full theory, the strong $CP$ problem has to be explained by an additional mechanism, e.g., the left-right and extended CP symmetry. Even though tree-level QCD theta parameter is restricted by the mechanism, radiative corrections to theta are mostly generated, which leads to a dangerous neutron electric dipole moment (EDM). The ordinary method for calculating the radiative theta utilizes an equation theta= -arg det m_q^{loop} based on the chiral rotations of complex quark masses. In this paper, we point out that when full theory includes extra heavy quarks, the ordinary method is unsettled for the extra quark contributions and does not contain its full radiative corrections. We formulate a novel method to calculate the radiative corrections to theta through a direct loop-diagrammatic approach, which should be more robust than the ordinary one. Then, we scrutinize a radiatively generated QCD theta parameter at the two-loop level based on both full analytical loop functions with the Fock-Schwinger gauge method and the effective field theory approach, using simplified models. We observe that the radiatively generated theta parameters at the low energy scale precisely match between them.

Belle II実験におけるステライルニュートリノ探索 (Tomoyuki Shimasaki)

素粒子標準理論においては、ニュートリノは左巻き成分のみを持ち質量をもたない粒子とされているが、ニュートリノ振動実験はニュートリノが小さいながらも質量をもつことを強く示唆している。右巻きで有限な質量をもつマヨラナ型の（ステライル）ニュートリノが存在すれば、小さいニュートリノ質量や宇宙初期のバリオジェネシスを説明し、さらに暗黒物質の候補にもなる[1]。 電子陽電子型衝突実験BelleまたはBelle IIではB中間子の崩壊過程を精密に調べることでGeV領域のステライルニュートリノ探索が可能である。先行研究Belleでは、2 - 3.5 GeV/c^2の質量領域においてステライルニュートリノとSMニュートリノとの混合定数Uに対して|U|^2~10^-4程度の制限を付けた[2]。本研究では、Belleとは異なる探索手法を用いてより小さな混合定数の領域での探索を目指す。 本トークでは、加速器実験としてのBelle IIの特徴と解析手法の基本的な事柄を述べた後、Belle IIにおけるステライルニュートリノ探索の戦略と現在の進捗について報告する。 参考文献： [1] Phys. Lett. B 620 (2005) [2] Phys. Rev. D. 87 071102 (2013)

Lepton number violation in the low-scale seesaw mechanism (Takehiko Asaka)

We investigate the origin of neutrino masses and its implications to the lepton number violation. Especially, we consider the seesaw mechanism by introducing right-handed neutrinos which mass scale is close to the weak scale. The contributions of such right-handed neutrinos to the lepton number violating processes, such as the neutrinoless double beta decay and the inverse neutrinoless double beta decay, are explained. In particular, we discuss the impact of the radiative corrections to these processes. 参考文献： T. Asaka, H. Ishida and K. Tanaka, ``Neutrinoless double beta decays tell nature of right-handed neutrinos,'' JHEP 07, 062 (2023) doi:10.1007/JHEP07(2023)062 [arXiv:2101.12498 [hep-ph]]. T. Asaka and T. Tsuyuki, ``Seesaw mechanism at electron-electron colliders,'' Phys. Rev. D 92, no.9, 094012 (2015) doi:10.1103/PhysRevD.92.094012 [arXiv:1508.04937 [hep-ph]].

複合非対称ダークマターの現象論 (Takumi Kuwahara)

アクシオンは強いCP問題を解決するPeccei–Quinn機構の枠組みで予言される擬南部ゴールドストンボソンである。微弱な結合を持ち安定である為、軽い暗黒物質の候補として考えられている。加えて、アクシオンの存在は宇宙発展に影響を及ぼし、とりわけ星の進化の様々な段階で観測されている冷却異常を説明する新たな冷却機構を与える。このような星の冷却異常を上手く説明するアクシオン模型（Variant DFSZ axion模型）はフレーバーを破る湯川結合を要求する。我々はVariant DFSZ axion模型において予言される125GeVヒッグスボソンのレプトンフレーバーを破る(LFV)崩壊の大きさについて詳細に解析を行った。本セミナーでは、このアクシオン模型が2023年に報告されたALTASのヒッグスボソンLFV崩壊におけるエクセスを説明出来ることを示す。また、このような拡張ヒッグスセクターを伴うアクシオン模型において、アクシオンとヒッグスボソンがどのように関連しているかについて議論する。 参考文献: JHEP 06 (2023) 208 (arXiv: 2303.03736) by TK, S.Yuan , JHEP 03 (2022) 176 (arXiv: 2112.01202) by A.Kamada, TK, work in progress by S.Das, A. Kamada, TK, K. Murase, D. Song

Dark matter self-interaction: the fate of the spike and annihilation-boosted dark matter in the Milky Way galaxy (Motoko Fujiwara)

One of the characteristic predictions of dark matter (DM) self-interaction is the number changing processes that convert n initial DM particles into m final ones (n to m process). The inner region of the Milky Way galaxy may host an extremely high density of DM, called DM spike, and can be an ideal environment to explore these n to m processes. We systematically study the consequences of n to m processes in the local galaxy, including all possible DM processes originating from the same interactions, such as annihilation and self-scattering. We find that for n > 2, the spike is depleted significantly by the annihilation and isothermal core formation via self-scattering, erasing the potential of the galactic center as a DM rich region. On the other hand, semi-annihilation processes of form 2 to 1 may maintain the spike power law and induce boosted DM signatures at direct detection and neutrino experiments. We can discriminate this boosting mechanism from others, thanks to its distinct recoil spectra with a sharp cutoff at the mass limit. We probe DM mass down to 2 MeV at CRESST (20 MeV at XENONnT) in evident complementarity with the signature from the Sun, where the evaporation mass (> 5 GeV) limits the sensitivity. Collaboration with: Boris Betancourt-Kamenetskaia, Alejandro Ibarra, and Takashi Toma (work in progress)

LFV decays of the Higgs boson in variant DFSZ axion models (Kodai Sakurai)

アクシオンは強いCP問題を解決するPeccei–Quinn機構の枠組みで予言される擬南部ゴールドストンボソンである。微弱な結合を持ち安定である為、軽い暗黒物質の候補として考えられている。加えて、アクシオンの存在は宇宙発展に影響を及ぼし、とりわけ星の進化の様々な段階で観測されている冷却異常を説明する新たな冷却機構を与える。このような星の冷却異常を上手く説明するアクシオン模型（Variant DFSZ axion模型）はフレーバーを破る湯川結合を要求する。我々はVariant DFSZ axion模型において予言される125GeVヒッグスボソンのレプトンフレーバーを破る(LFV)崩壊の大きさについて詳細に解析を行った。本セミナーでは、このアクシオン模型が2023年に報告されたALTASのヒッグスボソンLFV崩壊におけるエクセスを説明出来ることを示す。また、このような拡張ヒッグスセクターを伴うアクシオン模型において、アクシオンとヒッグスボソンがどのように関連しているかについて議論する。

Overview of flavor anomaly (Motoi Endo)

アブストラクト：物理量を精密に測定することで標準理論を超える新物理を見つ けることが期待されています。実験データの標準理論の予想からのズレは「アノ マリー」と呼ばれており、フレーバー物理に代表される精密測定実験では近年様 々なアノマリーが報告されてきました。とくに3シグマ（標準偏差）を超える大 きなズレもいくつか報告されおり、これが本当であれば新物理解明の有力な手が かりになります。近年の結果は果たして本当に新物理のシグナルなのか。このセ ミナーではとくに大きなズレをもつフレーバーアノマリーについて実験と理論の 現状を解説します。そしてもし本当に新物理のシグナルであれば今後どのような シナリオが考えられるのか紹介します。

行列正則化の一般化とその応用 (Satoshi Kanno)

行列正則化とは関数から行列への線型写像であり、いくつかの要請を満たすものである。 行列正則化は弦理論やM理論の行列模型による定式化において重要な役割を果たし、通常の空間の場の理論から非可換空間上の場の理論を構成する手法としても有用である。 さらに、近年量子コンピューターを場の理論に応用する際にも行列正則化がいい性質を持つと考えられている。 このように、弦理論、場の理論、量子計算分野などに対して行列正則化は重要である。 そこで、この行列正則化の具体的構成法や一般化を議論することは、これらの分野の発展のために意味があると考えられる。 本研究では、Berezin-Toeplitz量子化と呼ばれる手法を用いて、行列正則化を一般化することができることについて話す。 この研究は伊敷吾郎氏、足立宏幸氏との共同研究であり、arXiv:2210.01397,arXiv:2311.14984に基づく。

WIMP DM Heating in Neutron Stars (Natsumi Nagata)

Weakly Interacting Massive Particles (WIMPs) in the Universe accumulate in neutron stars (NSs) through their interactions with ordinary matter, and their annihilation inside the NS core causes late-time heating. It has been argued that this heating effect maintains the surface temperature of old NSs to be a few thousand K, which can be regarded as a smoking gun signature of dark matter (DM) heating in NSs. In this talk, I will review this DM heating mechanism and discuss its feasibility, as well as its implications for testing WIMP DM models.

ヒッグスセクターと新物理、地上実験と宇宙実験での検証 (Shinya Kanemura)

このセミナーでは、標準理論におけるヒッグスセクターの脆弱性とそこから生じる拡張性に注目し、拡張されたヒッグスセクターに関する一般的な議論から始めます。一方、標準理論では説明できないいくつかの問題が知られており、それを説明する物理模型にはしばしば特徴のある拡張ヒッグスセクターが導入されています。これらについていくつか紹介します。その中でもバリオン数非対称性問題はヒッグス物理と密接に関係している可能性があり、理論的観点からも実証性の観点からも大変興味をそそられます。この方向の物理模型について解説します。そして、理論研究と将来実験によって得られるヒッグスセクターの物理の真の理解が標準理論を超える新物理に至る鍵になるという立場で、将来の高エネルギー加速器実験、フレーバー実験、重力波観測、原始ブラックホール探索などを駆使することにより、いかにしてヒッグスセクターの構造を絞り込んでいき、そこから標準理論を超える新物理学に迫るかという話をします。

Reference: [1] H-COUP ver3 M. Aiko, S. Kanemura, M. Kikuchi, K. Sakurai, K. Yagyu 2311.15692 [2] New application of the mass-dependent analysis for renormalization group equation to extended Higgs sectors S. Kanemura, Y. Mura, 2310.15622 [3] Electroweak Baryogenesis via top-charm mixing S. Kanemura, Y. Mura, 2303.11052 [4] その他多数

The birth of binary compact objects (Kazumi Kashiyama)

Ground-based gravitational wave interferometers like advanced LIGO, advanced VIRGO, and KAGRA have increasingly detected gravitational waves originating from the merging of binary compact objects, comprising black holes and neutron stars. How, when, and where these binary compact objects form are of immense astrophysical interest. In this presentation, I will focus on the peculiar explosive phenomena associated with the birth of binary compact objects, elaborating on their recently unveiled properties, and exploring future prospects in multi-messenger time-domain astronomy related to this subject.

Lepton Flavor and Neutrino Oscillation (Joe Sato)

Lepton flavor is an exact symmetry in the standard model. Though it is exact, it is global and accidental. Indeed it is easy to be broken by extending the SM. Therefore the search for its violation has been made since the discovery of the second flavor, muon. In this lecture we first derive the lepton flavor in the SM and see how accidental it is and how easily it is broken. It's violation is indeed seen in the neutrino oscillation phenomena. Experimentally to see its violation what we should observe and along this direction we see the reason why the neutrino oscillation is indeed interpreted as its violation. Finally we discuss how we should extend the SM to include lepton flavor violation.

21cm line as a probe of BSM (Tomo Takahashi)

PThe redshifted 21cm line of neutral hydrogen would be a very useful probe of scenarios beyond the standard model (BSM). First I briefly review the physics of the 21cm line of neutral hydrogen, particularly focusing on the signal from the so-called dark ages. Then I will discuss some examples of how the 21cm signal can be used to probe BSM: the nature of dark matter beyond the standard CDM, dark components of the Universe such as early dark energy, and so on. Future prospects for the 21cm line observations and its implications for BSM will also be briefly discussed.

A primordial black hole tale: from cosmological aspects to astrophysical searches (Joaquim Iguaz)

Primordial Black Holes (PBHs) can form in the very early universe and can be associated with numerous cosmological and astrophysical signatures. In this talk, I will explore the physics related to PBHs from their possible formation in the earliest stages of the universe to the possible signatures of a population of PBHs in our own galaxy. I present here a fascinating story with PBHs as the main characters, playing the roles of Dark Matter (DM), coalescing objects detected by LIGO/Virgo, and Supermassive Black Holes (SMBHs). After an introduction, the bulk of the presentation is divided into three main sections. Firstly, I will discuss the possible formation of PBHs during the preheating phase that immediately follows inflation. Secondly, I will present a discussion on the implications of early universe phenomena, most notably the quantum chromodynamics (QCD) phase transition and electron-positron annihilation, on the mass distribution of PBHs forming at these epochs. I will then analyze the constraints on this scenario from a number of observations: the specific pattern in cosmic microwave background (CMB) anisotropies induced by accretion onto PBHs, CMB spectral distortions, gravitational wave searches, and direct counts of SMBHs at high redshift. Finally, I will discuss the evaporation of light PBHs via Hawking evaporation and its possible observable signatures on the measured Galactic and isotropic gamma ray fluxes. No PBH signal is detected, and the strongest limit on PBH DM in the mass range under study is set.

Dynamical small field inflation triggered in the supercooled universe (Hiroyuki Ishida)

Coleman-Weinberg (CW) mechanism gives the origin of symmetry breaking by quantum effects and the potential easily gives long journey along the flat direction which would be a candidate to accommodate the cosmological inflation at the low energy scale compared to the usual chaotic inflation. However, such a low scale inflation, small field inflation (SFI), would be suffered from a tuning problem of the initial inflaton field value. We propose a dynamical solution to the problem and show the mechanism can work consistently with observed constraints on the inflation parameters.

Formulation of mixed/polychronic tunneling in a quantum many-body system (Yutaro Shoji)

Quantum tunneling in a many-body system is a much more non-trivial process than that in a one-body system. One example is the mixed tunneling, which has been discussed and observed for a long time. Suppose there are two coupled particles and only one of them feels a potential barrier. When we try to describe the tunneling process of these particles, we face a problem; while one particle is tunneling, the other particle is moving in real time. There exist several ways to treat this type of tunneling, but there is no method that can be easily handled and is derived from first principles. We obtained a path-integral formula based on the local energy conservation law and extended it to quantum field theory and quantum gravity.

原子超流動体中の不純物間に働くファン・デル・ワールス力 (Masaru Hongo)

近年のレーザー技術の発達により，絶対零度に近い極低温（数十ナノケルビン程度）の原子気体を高精度で制御することが可能となり，ミクロな世界の物理法則を支配する量子力学の効果を直接調べられるようになってきた．このセミナーでは，原子気体を極適温に冷やしたときに実現する超流動体中に，不純物2つの間に働く長距離力について調べた我々の研究[1]について紹介する．2つの不純物間には湯川ポテンシャルで記述される力が働くことが知られており[2]，これらを長距離に離していくと力は指数関数的に小さくなるとこれまで信じられていた．我々は，ポテンシャルの長距離でのふるまいを支配するのは超流動フォノンという南部・ゴールドストーンモードであることに注目し，その有効場の理論を用いて，これまでは考慮されていなかった量子揺らぎにより誘導される力を評価した．その結果，長距離における不純物間ポテンシャルが，2つの超流動フォノンの交換に起因するファン・デル・ワールス力で普遍的に記述されることを示した．セミナーでは主にゼロ温度のときの結果について紹介するが，有限温度にしたときにどのように修正を受けるかについても紹介する

[1] K. Fujii, M. Hongo, T. Enss, Phys. Rev. Lett. 129, 233401 (2022)
[2](e.g.) C. J. Pethick, H. Smith, "Bose-Einstein Condensation in Dilute Gases" Cambridge University Press (2008)

Special Lecture: 有効場の理論入門ー非相対論的多体問題を例にして (Masaru Hongo)

6/21 (lecture 1) 14:45-16:15, (lecture 2) 16:30-18:00
6/22 (lecture 3) 10:30-12:00, (lecture 4) 13:00-14:30, (lecture 5) 14:45-16:15
6/23 (lecture 6) 10:30-12:00, (seminar) 13:00-14:30
The schedule is tentative.

Asymmetric SIMP Dark Matter (Shu-Yu Ho)

In this paper, we construct the first asymmetric strongly interacting massive particles (SIMP) dark matter (DM) model, where a new vector-like fermion and a new complex scalar both having nonzero chemical potentials can be asymmetric DM particles. After the spontaneous breaking of a U(1)D dark gauge symmetry, these two particles can have accidental Z4 charges making them stable. By adding one more complex scalar as a mediator between the SIMP DM, the relic density of DM is determined by 3 → 2 and two-loop induced 2 → 2 annihilations and dark asymmetry in this model. On the other hand, the SIMP DM can maintain kinetic equilibrium with the thermal bath until the DM freeze-out temperature via the new gauge interaction. Interestingly, this model can have a bouncing effect on DM, whereby the DM number density rises after the chemical freeze-out of DM. With this effect, the prediction of the DM self-interacting cross section in this model can be consistent with astrophysical observations, and the ratio of the DM energy density to the baryonic matter energy density can be explained by primordial asymmetries. We also predict the DM-electron elastic scattering cross section that can be used to test this model in future projected experiments.

Reference: Shu-Yu Ho, arXiv:2207.13373 [hep-ph]

Multi-photon signatures at LHC and future linear colliders as a probe of CP-Violation in 2HDMs (Kento Katayama)

We discuss signatures of CP-violating (CPV) two Higgs doublet models at LHC and future linear colliders, where CPV appears from Yukawa interactions and the Higgs potential. In particular, we consider the scenario with the Yukawa alignment to avoid tree level flavor changing neutral currents. In addition, we consider the Higgs alignment in which the couplings of the discovered Higgs boson are taken to be the same as those in of the SM Higgs boson at tree level. We find that branching ratios of both the extra neutral Higgs bosons into diphoton can be simultaneously significant due to the constructive effect of the fermion and charged Higgs loops if CPV phase in the potential is nonzero. We show that the CPV of the Higgs sector can be tested via the three or four photon final states from the pair production of the extra Higgs bosons at LHC and future linear colliders under constraints from electric dipole moments.

Abstracts (academic year 2022)

Abstracts (academic year 2021)

Abstracts (academic year 2020)