Wen Yin, University of Tokyo
Messengers of reheating phase and their spectra
Online (Zoom), indico page, slides (kek.jp only) After inflation, the Universe presumably undergoes a phase of reheating which in effect starts the thermal big bang cosmology. However, so far we have very little direct experimental or observational evidence of this important phase of the Universe. I would like to argue that measuring the spectrum of freely propagating relativistic particles produced during reheating may provide us with powerful information on the reheating phase. To demonstrate this possibility, we first discuss which kind of (SM,BSM) particle can play the role of the messenger of reheating. Then we show that the spectrum crucially depends on whether the mother non-relativistic particle once dominated the Universe or not.
After inflation, the Universe presumably undergoes a phase of reheating which in effect starts the thermal big bang cosmology. However, so far we have very little direct experimental or observational evidence of this important phase of the Universe. I would like to argue that measuring the spectrum of freely propagating relativistic particles produced during reheating may provide us with powerful information on the reheating phase. To demonstrate this possibility, we first discuss which kind of (SM,BSM) particle can play the role of the messenger of reheating. Then we show that the spectrum crucially depends on whether the mother non-relativistic particle once dominated the Universe or not.
Characteristic features caused by the dependence on the number of the relativistic degrees of freedom may even allow to infer the temperature when the decay of the heavy particle occurred. This talk is based on
2007.15006 and 2102.00006.
Shih-Yen Tseng, The University of Tokyo
Alternative Minimal U(1)B-L
Online (Zoom), indico page, slides (kek.jp only)
We propose a minimal alternative gauged U(1)B-L model in which three right-handed neutrinos with charges of (5,-4,-4) and only one B-L Higgs field with charge 1 are introduced. Consistent active neutrino masses and mixings can be obtained if a Z2 symmetry on two of the right-handed neutrinos is introduced. It predicts two heavy degenerate right-handed neutrinos, which may realize the resonant leptogenesis scenario, and one relatively light sterile neutrino, which is a good dark matter candidate.
笠 真生, Princeton University
[KEK連携コロキウム]トポロジカル相と部分転置
Online (Zoom)
量子多体系では、古典系との類似を持たない様々な創発的な現象が実現されうる。通常の自発的対称性の破れで特徴づけられない、トポロジカル相はその一例である。本講演では、部分転置とよばれる量子情報理論で使われる操作を使って、トポロジカル相の様々な性質を議論する。一例として、部分転置を使って時間反転対称性で保護されたトポロジカル相（トポロジカル絶縁体など）のトポロジカル不変量を構成できることを示す。この不変量は、よく議論される自由電子系（バンド理論）におけるトポロジカル不変量（例えばKane-Meleによるもの）とは異なり、相互作用がある系にも適用される。部分転置は、また、エンタングルメントネガティビティと呼ばれる混合状態に対する量子もつれの測度の構成にも使うことができる。講演では、トポロジカル相に存在する準粒子であるエニオンの性質を、エンタングルメントネガティビティを使って議論する。
Motoko Fujiwara, Nagoya University
A model of electroweakly interacting non-abelian vector dark matter
Online (Zoom), indico page, slides (kek.jp only)
We propose a new electroweakly interacting spin-1 dark matter(DM) model. In our model, DM pairs annihilate into SM particles through the electroweak interaction efficiently. Therefore, we can explain the correct DM energy density via the freeze-out mechanism while evading the current experimental bounds. In this talk, we present how we constructed this spin-1 DM model. We also show the parameter region where we obtain the correct DM energy density and discuss the future detectability of this model. This talk is based on JHEP 07 (2020) 136 [arXiv:2004.00884].
Masazumi Honda (YITP, Kyoto University)
Quantum simulations of gauge/string/M-theory and via matrix quantum mechanics
Online (Zoom), indico page, slides (kek.jp only)
This talk consists of two parts. In the first part, I am going to talk on our proposal on a new framework for simulating U(k) Yang-Mills theory on a universal quantum computer. This construction utilizes the orbifold lattice formulation proposed by Kaplan, Katz, and Unsal, who originally applied it to supersymmetric gauge theories. Our proposed approach yields a novel perspective on quantum simulation of quantum field theories, carrying certain advantages over the usual Kogut-Susskind formulation. In the second part, I am going to present a novel framework for simulating matrix models on a quantum computer. Supersymmetric matrix models have natural applications to superstring/M-theory and gravitational physics, in an appropriate limit of parameters. Furthermore, for certain states in the Berenstein-Maldacena-Nastase (BMN) matrix model, several supersymmetric quantum field theories dual to superstring/M-theory can be realized on a quantum device. This talk is based on collaborations with Alexander Buser, Hrant Gharibyan, Masanori Hanada and Junyu Liu.
Masazumi Honda, February, YITP, Kyoto University
Digital quantum simulation of the Schwinger model with topological
Online (Zoom), indico page, slides (kek.jp only)
I am going to talk about application of quantum computation to numerical simulation of quantum field theory. Specifically we implement a digital quantum simulation of a gauge theory with a topological term in Minkowski spacetime, which is practically inaccessible by standard lattice Monte Carlo simulations. We focus on 1+1 dimensional quantum electrodynamics with the θ-term known as the Schwinger model. We construct the true vacuum state of a lattice Schwinger model using adiabatic state preparation which, in turn, allows us to compute an expectation value of the fermion mass operator with respect to the vacuum. Upon taking a continuum limit we find that our result in massless case agrees with the known exact result. In massive case, we find an agreement with mass perturbation theory in small mass regime and deviations in large mass regime. We also study the confinement versus screening problem in the Schwinger model. Our results imply that digital quantum simulation is already useful tool to explore non-perturbative aspects of gauge theories with real time and topological terms. This talk is based on collaborations with Bipasha Chakraborty, Etsuko Itou, Taku Izubuchi, Yuta Kikuchi, Lento Nagano, Takuya Okuda and Akio Tomiya.
Takahisa Igata, KEK
[Cosmophys seminar] Photon escape probability from the vicinity of a Kerr black hole
Online (Zoom)
With the recent development of black hole shadow observations, phenomena in the vicinity of an event horizon have become a subject of observations. In this seminar, we will focus on a light source in the vicinity of a Kerr black hole and consider an escape probability and frequency shift of photons emitted from the source to infinity. We also discuss how the proper motion of the source affects these observational indices.
Denny Lane B. Sombillo, Osaka University
Application of deep learning to the study of near-threshold resonances
Online (Zoom), indico page, slides (kek.jp only)
Peak structures in the scattering experiments are often interpreted as a manifestation of a resonance state. A more rigorous approach requires that we associate at least one S-matrix pole to the peak structure to qualify as a physical state. The presence of a nearby threshold complicates the situation. Sometimes, near-threshold virtual and quasi-bound states produce a similar peak structure. In our work, we phrased the problem as a classification task and solved them using deep learning. In the first part of this talk, I will discuss how deep learning is applied to distinguish virtual and bound state enhancements in the single-channel nucleon-nucleon system. Even without appealing to deuteron’s existence, our deep neural network models can distinguish the two enhancements. In the last part, I will discuss how this approach can be extended to the coupled-channel problem. Specifically, we designed a deep neural network that can extract the coupled-channel S-matrix pole configuration. The resulting training dataset requires a nonconventional training loop; otherwise, the deep neural network will not learn. Finally, we apply our model to the study of the pion-nucleon scattering near the eta-nucleon threshold. I will also discuss some preliminary results.
Toyokazu Sekiguchi, KEK
[Cosmophys seminar] Revisiting constraints on dark matter annihilation from global 21cm signals
Online(Zoom)
When dark matter annihilation takes place in the Universe at high redshifts (between recombination and reionization), energetic particles are injected into intergalactic medium (IGM), which is filled with neutral hydrogen. By ionizing and heating IGM, dark matter annihilation can affect redshifted 21cm signals, which EDGES have claimed to detect for the first time. After reviewing how redshifted 21cm signals are modified by dark matter annihilation, we revisit the constraints based on the EDGES result. In particular, we’ve performed dedicated N-body simulations in order to estimate dark matter clumpiness, as known as boost factor, which has results in constraints more conservative than previously estimated.
Kazuki Enomoto, Osaka University
Higher dimensional LNV operators and their renormalization
Online (Zoom), indico page, slides (kek.jp only)
