セミナー

Arnab Chaudhuri, National Astronomical Observatory of Japan

Dark matter production from two evaporating PBH distributions

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Particulate dark matter (DM), completely isolated from the Standard Model particle sector, can be produced in the early Universe from primordial black hole (PBH) evaporation. However, big bang nucleosynthesis (BBN) observations put an upper bound on the initial mass of PBH requiring the PBH to evaporate completely before the advent of BBN. DM particles in the mass range ∼(1–10^9)GeV cannot explain the observed relic abundance for an early matter dominated universe due to this BBN constraint. However, this assumes the presence of only one monochromatic PBH mass distribution in the early Universe. In this talk, we will explore the simple possibility of achieving the observed relic with DM masses from the above mentioned range for an early matter dominated era with two monochromatic evaporating PBH mass distributions and demonstrate that the fermionic DM masses consistent with BBN change slightly.

Ryutaro Matsudo, NTU

Boundary condition and reflection anomaly in 2+1 dimensions

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
t is known that the 2+1d single Majorana fermion theory has an anomaly of the reflection, which is canceled out when 16 copies of the theory are combined. Therefore, it is expected that the reflection symmetric boundary condition is impossible for one Majorana fermion, but possible for 16 Majorana fermions. In this study, we consider a reflection symmetric boundary condition that varies at a single point, and find that there is a problem with one Majorana fermion. The problem is the absence of a corresponding outgoing wave to a specific incoming wave into the boundary, which leads to the non-conservation of the energy. For 16 Majorana fermions, it is possible to connect every incoming wave to an outgoing wave without breaking the reflection symmetry. In addition, we discuss the connection with the fermion-monopole scattering in 3+1 dimensions. This talk is based on arXiv:2306.10845.

羽澄昌史, 量子場計測システム国際拠点

[金茶会] 第7回 すべての量子を使い倒せ — QUPと宇宙・素粒子・社会

つくば:3号館セミナーホール (リモート会場:J-PARC研究棟2階会議室)

https://www-conf.kek.jp/kincha/

Jongkuk Kim, KIAS

Recent B->Kνν and muon g-2 anomalies in U(1)_{L_\mu - L_\tau}- charged DM model

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom

The Belle II collaboration recently announced that they observed the B → Kνν decay process for the first time. This dineutrino mode of B+ → K+ν¯ν has been theoretically identified as a very clean channel. However, their result encounters a 2.8σ deviation from the Standard Model (SM) calculation. On the other hand, last year, Fermilab released new data on muon (g − 2) away from the SM expectation with 5σ. In this talk, we will study the simplest UV-complete U(1)Lµ−Lτ -charged Dark Matter (DM) model.
Thanks to the existence of dark Higgs boson and dark photon in this model, we can explain the observed relic density of DM and resolve the anomalous results reported by both Belle II and Fermilab experiments simultaneously without any modification of the thermal history of the Universe.

Masanori Hanada, Queen Mary University of London

[QCD theory seminar] Color Confinement and Random Matrices

Oneine (Zoom)
We describe how the general mechanism of partial deconfinement applies to large-N QCD and the partially deconfined phase inevitably appears between completely-confined and completely-deconfined phases. Furthermore, we propose how the partial deconfinement can be observed in the real-world QCD with the SU(3) gauge group. For this purpose, we employ lattice configurations obtained by the WHOT-QCD collaboration and examine our proposal numerically. In the discussion, the Polyakov loop plays a crucial role in characterizing the phases, without relying on center symmetry, and hence, we clarify the meaning of the Polyakov loop in QCD at large N and finite N. As a nontrivial test for our proposal, we also investigate the relation between partial deconfinement and instanton condensation and confirm the consistency with the lattice data. As a nontrivial application, we show that computation of the two-point correlator of Polyakov loops in the confined phase reduces to the problem of random walk on group manifold. As a consequence, linear confinement potential with approximate Casimir scaling follows immediately.

Ten Brandes, Munich Tech U

Constraints on Phase Transitions in Neutron Star Matter

Online (Zoom)
Recent inference results of the sound velocity in the cores of neutron stars are summarized. Implications for the equation of state and the phase structure of highly compressed baryonic matter are discussed. In view of the strong constraints imposed by the heaviest known pulsars, the equation of state must be very stiff in order to ensure the stability of these extreme objects. This required stiffness limits the possible appearance of phase transitions in neutron star cores. For example, a Bayes factor analysis quantifies strong evidence for squared sound velocities c_s^2 > 0.1 in the cores of 2.1 solar-mass and lighter neutron stars. Only weak first-order phase transitions with a small phase coexistence density range \Delta\rho/\rho < 0.2 (at the 68\% level) in a Maxwell construction still turn out to be possible within neutron stars. The central baryon densities in even the heaviest neutron stars do not exceed five times the density of normal nuclear matter. In view of these data-based constraints, much discussed issues such as the quest for a phase transition towards restored chiral symmetry and the active degrees of freedom in cold and dense baryonic matter, are reexamined.

Aleskey Cherman, MInnesota U

Exact lattice chiral symmetry in 2d gauge theory

Online (Zoom)
Preserving the symmetries of massless fermions is a well-known challenge in lattice field theory. I’ll discuss symmetry-preserving lattice regularizations of 2d QED with one and two flavors of Dirac fermions, as well as the `3450′ chiral gauge theory. The construction leverages bosonization and recently-proposed modifications of Villain-type lattice actions. The internal global symmetries act just as locally on the lattice as they do in the continuum, the anomalies are reproduced at finite lattice spacing, and in each case we’ve found a sign-problem-free dual formulation.

鈴木勝彦, 海底資源センター

[金茶会] 第6回 海洋鉱物資源:放射光や同位体を用いた有用金属濃集プロセスの研究から環境影響評価まで

東海:J-PARC研究棟2階会議室 (リモート会場:つくば3号館セミナーホール)

https://www-conf.kek.jp/kincha/

Xiaojun Yao, Univ. of Washington

[QCD theory seminar] When is axial gauge applicable?

Oneine (Zoom)
Axial gauge has been used in many perturbative calculations. However, it sometimes leads to puzzling results. In this talk, I will discuss a specific example in the context of heavy quark and quarkonium transport coefficients, where naive application of temporal axial gauge leads to an incorrect result. Then I will discuss the origin of the problem from both perturbative and nonperturbative aspects. Finally I will summarize the applicability condition of axial gauge and give a few examples.

Ippei Obata, KIPMU

Parity-violating scalar trispectrum from axion inflation

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
We study a mechanism of generating the trispectrum (4-point correlation) of curvature perturbation through the dynamics of a spectator axion field and U(1) gauge field during inflation. Owing to the Chern-Simons coupling, only one helicity mode of the gauge field experiences a tachyonic instability and sources scalar perturbations. Sourced curvature perturbation exhibits parity-violating nature which can be tested through its trispectrum. We numerically compute the parity-even and parity-odd components of the sourced trispectrum. It is found that the ratio of parity-odd to parity-even mode can reach O(10%) in an exact equilateral momentum configuration. We also investigate a quasi-equilateral shape where only one of the momenta is slightly longer than the other three, and find that the parity-odd mode can reach, and more interestingly, surpass the parity-even one. This may help us to interpret a large parity-odd trispectrum signal extracted from BOSS galaxy-clustering data.

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