2018年度のセミナー

Date/Place Jul. 31th (Tue.) 15:30-16:30 / H711
Name Teruaki Suyama (Titech)
Title Primordial black holes in the era of gravitational wave astronomy
Abstract Black holes might have formed in the very early universe before the big bang nucleosynthesis. Those black holes, known as primordial black holes(PBHs), behave as dark matter, and there are a lot of studies about whether PBHs can explain all dark matter or not. The recent discovery of binary black holes by LIGO has led to a resurgence of the PBH hypothesis. In this talk, I will present my recent study which showed a possibility that LIGO black holes are PBHs. I will also discuss about how to test the PBH hypothesis by future gravitational wave observations.

 

Date/Place Jul. 30th (Mon.) (Informal) 16:00-17:00 / H711
Name Kenji Kadota (IBS)
Title Particle cosmological probes on the light dark matter (Slides)
Abstract A few examples for the light dark matter will be discussed with an emphasis to illustrate the complementarity between the particle physics and cosmology probes.

 

Date/Place Jul. 24th (Tue.) 15:30-16:30 / H711
Name Masazumi Honda (Weizmann Institute of Science)
Title Introduction to Resurgence and Complex saddle point analysis (Slides)
Abstract Resurgence is a technique to resum asymptotic perturbative series which has often reproduced exact results in various problems. This talk will focus on applications of resurgence for weak coupling perturbative series of quantities represented by (path) integrals. I will discuss that in this type of problems, we have to perform saddle point analysis "seriously". Namaly, we need to take care of global steepest decsents (Lefschetz thimble) and complex saddle points which are not on original (path) integral contour. I will demonstrate these points in terms of very simple examples. I will also briefly mention recent applications of Lefschetz thimble to various problems.

 

Date/Place Jul. 18th (Wed.) (Informal) 13:30- / H711
Name Shinji Hirano (Wits & Yukawa Inst.)
Title Airy Function and 4d Quantum Gravity
Abstract We study 4d quantum gravity with negative cosmological constant in the minisuperspace approximation and compute the partition function for the S^3 boundary geometry. In this approximation scheme the path integrals become dominated by a class of asymptotically AdS "microstate geometries." Despite the fact that the theory is pure Einstein gravity without supersymmetry, the result precisely reproduces, up to higher curvature corrections, the Airy function in the S^3 partition function of the maximally supersymmetric Chern-Simons-matter (CSM) theory which sums up all perturbative 1/N corrections. We also show that this can be interpreted as a concrete realization of the idea that the CFT partition function is a solution to the Wheeler-DeWitt equation as advocated in the holographic renormalization group. Furthermore, the agreement persists upon the inclusion of a string probe and it reproduces the Airy function in the vev of half-BPS Wilson loops in the CSM theory.

 

Date/Place Jul. 17th (Tue.) 15:30-16:30 / H711
Name Kohtaro Tamaoka(Osaka University)
Title Towards Entanglement of Purification for Conformal Field Theories (Slides)
Abstract We argue that the entanglement of purification for two dimensional holographic CFT can be obtained from conformal blocks with internal twist operators. First, we explain our formula from the view point of tensor network model of holography. Then, we apply it to bipartite mixed states dual to subregion of AdS3 and the static BTZ blackhole geometries. The formula in CFT agrees with the entanglement wedge cross section in the bulk, which has been recently conjectured to be equivalent to the entanglement of purification.

 

Date/Place Jul. 17th (Tue.) (Informal) 13:15- / H711
Name Masazumi Honda (Weizmann Institute of Science)
Title Cardy Formula for 4d SUSY Theories and Localization
Abstract We study 4d N=1 supersymmetric theories on a compact Euclidean manifold of the form S^1xM_3. Partition functions of gauge theories on this background can be computed using localization, and explicit formulas have been derived for different choices of the compact manifold M_3. Taking the limit of shrinking S^1, we present a general formula for the limit of the localization integrand, derived by simple effective theory considerations, generalizing the result of arXiv:1512.03376. The limit is given in terms of an effective potential for the holonomies around the S^1, whose minima determine the asymptotic behavior of the partition function. If the potential is minimized in the origin, where it vanishes, the partition function has a Cardy-like behavior fixed by Tr(R), while a nontrivial minimum gives a shift in the coefficient. In all the examples that we consider, the origin is a minimum if Tr(R)≤0.

 

Date/Place Jul. 10th (Tue.) 15:30-16:30 / H711
Name Kei Yagyu (Seikei University)
Title SUSY VS Compositeness: 2HDMs tell the story (Slides)
Abstract Although a Higgs boson was discovered at the LHC, we still do not know what is the Nature of the Higgs boson. So far, two big paradigms have been discussed to clarify the Nature of the Higgs boson, namely, supersymmetry and compositeness, where Higgs physics is described by weak and strong dynamics, respectively. Both of these scenarios predict a 2-Higgs doublet model (2HDM) as a low energy effective theory. In this talk, we discuss how we can determine the true dynamics at a TeV scale by focusing on differences in various properties of the 2HDM.

 

Date/Place July. 3th (Tue.) 15:30-16:30 / H711
Name Takao Suyama (KEK)
Title \theta=\pi in SU(N)/Z_N Theory
Abstract In SU(N) gauge theory, it is argued recently that there exists a "mixed anomaly" between the CP symmetry and the 1-form ZN symmetry at θ=π, and the anomaly matching requires CP to be spontaneously broken at θ=π if the system is in the confining phase. In this paper, we elaborate on this discussion by examining the large volume behavior of the partition functions of the SU(N)/ZN theory on T4 a la 't Hooft. The periodicity of the partition function in θ, which is not 2π due to fractional instanton numbers, suggests the presence of a phase transition at θ=π. We propose lattice simulations to study the distribution of the instanton number in SU(N)/ZN theories. A characteristic shape of the distribution is predicted when the system is in the confining phase. The measurements of the distribution may be useful in understanding the phase structure of the theory.

 

Date/Place Jun. 26th (Tue.) 15:30-16:30 / H711
Name Yoshio Kikukawa (Univ. of Tokyo)
Title On the gauge invariant path-integral measure for the overlap Weyl fermoins in 16 of SO(10)
Abstract We consider the lattice formulation of SO(10) chiral gauge theory with left-handed Weyl fermions in the sixteen dimensional spinor representation (16) within the framework of the Overlap fermion/the Ginsparg-Wilson relation. We define a manifestly gauge-invariant path-integral measure for the left-handed Weyl field using all the components of the Dirac field, but the right-handed part of which is just saturated completely by inserting a suitable product of the SO(10)-invariant 't Hooft vertices in terms of the right-handed field. The measure possesses all required transformation properties under lattice symmetries and the induced effective action is CP invariant.

 

Date/Place Jun. 22nd (Fri.) 12:10-13:10 / H711
Name Hermann Nicolai (Max Planck Institute)
Title The Conformal Standard Model (Slides)
Abstract The Conformal Standard Model (CSM) is a minimal extension of the Standard Model of Particle Physics based on the assumed absence of large intermediate scales between the TeV scale and the Planck scale, which incorporates only right-chiral neutrinos and a new complex scalar in addition to the usual SM degrees of freedom, but no other features such as supersymmetric partners. In this talk I will present an overview and argue that all outstanding issues of particle physics proper can in principle be solved ‘in one go’ within this framework. The main testable prediction of the model is a new and almost sterile scalar boson that would manifest itself as a narrow resonance in the TeV region.

 

Date/Place Jun. 12th (Tue.) 15:30-16:30 / H711
Name Motoi Endo (KEK)
Title Revisiting TeV-scale SUSY (Slides)
Abstract Although no new particles have been discovered in the LHC experiments, SUSY has been one of the most attractive scenarios of physics beyond the SM. In this talk, we overview the status and prospects of SUSY in a TeV scale. In particular, we will show that some of the flavor anomalies are (still) explained well by the scenarios without conflicting with the LHC and other constraints.

 

Date/Place Jun. 8th (Fri.) 13:30-14:30 / H711
Name Takeo Moroi (Univ. of Tokyo)
Title Stability of Electroweak Vacuum in the Standard Model and Beyond (Slides)
Abstract I will discuss recent progresses of the calculation of the decay rate of the electroweak vacuum in the standard model. I will also discuss how extra fermions may affect the stability of the electroweak vacuum.

 

Date/Place May. 29th (Tue.) 15:30-16:30 / H711
Name Shoji Hashimoto (KEK)
Title Quark-hadron duality and lattice QCD
Abstract Quark-hadron duality is a basic assumption which many perturbative QCD calculations rely on. There are plausible arguments about why it is valid, but only at a qualitative level. We propose a set of quantities for which quantitative and non-perturbative calculation is possible using lattice QCD. A well-known example is related to the R-ratio of e+e- scattering. A primary target of the method discussed in this talk is the inclusive decays of B mesons. We discuss on how one can calculate its decay rate or some related quantities.

 

Date/Place May. 23th (Wed.)(Informal) 12:10-1:10 / H711
Name Janusz Rosiek (University of Warsaw)
Title Decay of Higgs boson to photons in the Standard Model Effective Field Theory (Slides)
Abstract Potential effects of yet undiscovered New Physics can be universally parametrized in terms of the so-called SM Effective Field Theory, defined as the Standard Model extended with all gauge-invariant operators of higher dimensions constructed of the SM fields. I will discuss a consistent setup for the perturbative calculations in such a complicated (non-renormalizable) model, including derivation of the Feynman rules in terms of the physical fields and quantization of the theory in the R_xi gauges. Then, as an application I will present the calculation of the radiative decay of Higgs boson into 2 photons in SMEFT.

 

Date/Place May. 22th (Tue.) 15:30-16:30 / H711
Name Toshifumi Noumi (Kobe Univ.)
Title Weak Gravity Conjecture and Infrared Consistency (Slides)
Abstract As is captured by the word “string landscape,” an almost infinite number of low-energy effective theories may be described in the string theory framework. However, recent studies have revealed that there exist a certain class of consistent-looking IR effective theories which are not realized in string theory, or more generally in a consistent UV theory of quantum gravity. Such theories are said to live in the “swampland” and clarifying the boundaries of landscape and swampland is an important issue in both the theoretical and phenomenological contexts. In the first half of this talk, I will review a typical example for such a criterion called the Weak Gravity Conjecture and its phenomenological implications. In the latter half, I will discuss its possible connection to other QFT principles such as unitarity. In particular, I will introduce our new proposal which we call the Tower Weak Gravity Conjecture based on the recent work arXiv:1802.04287.

 

Date/Place May. 15th (Tue.) 15:30-16:30 / H711
Name Tatsuma Nishioka (Univ. of Tokyo)
Title OPE for Conformal Defects and Holography
Abstract We study the operator product expansion(OPE) for scalar conformal defects of any codimension in CFT. The OPE for defects is decomposed into “defect OPE blocks”, the irreducible representations of the conformal group, each of which packages the contribution from a primary operator and its descendants. We use the shadow formalism to deduce an integral representation of the defect OPE blocks. They are shown to obey a set of constraint equations that can be regarded as equations of motion for a scalar field propagating on the moduli space of the defects. By employing the Radon transform between the AdS space and the moduli space, we obtain a formula of constructing an AdS scalar field from the defect OPE block for a conformal defect of any codimension in a scalar representation of the conformal group, which turns out to be the Euclidean version of the HKLL formula. We also introduce a duality between conformal defects of different codimensions and prove the equivalence between the defect OPE block for codimension-two defects and the OPE block for a pair of local operators.

 

Date/Place May. 8th (Tue.) 15:30-16:30 / H711
Name Sugumi Kannno (Osaka Univ.)
Title Quantum entanglement between bubble universes (Slides)
Abstract In de Sitter space where the universe expands exponentially, any two of mutually separated regions eventually become causally disconnected. This is most conveniently described by spanning open universe coordinates on two open charts in de Sitter space. Recently, Maldacena and Pimentel showed that the entanglement entropy of a free massive scalar field between two open charts is non-vanishing. This result shows that two causally disconnected regions in de Sitter space are entangled. I extend the calculation of Maldacena and Pimentel to the case where a bubble wall is present between the two open charts. This can be thought of as a model of pair creation of bubble universes in de Sitter space. I will discuss the effect of the bubble wall on the entanglement entropy between the bubble universes.

 

Date/Place Apr. 24th (Tue.) 15:30-16:30 / H711
Name Chen Zhang (NCTS)
Title Simplest Little Higgs Revisited: Hidden Mass Relation, Unitarity and Naturalness (Slides)
Abstract In this talk, I will present an analysis of the scalar potential of the Simplest Little Higgs (SLH) model in an approach consistent with the spirit of continuum effective field theory (CEFT). A hidden mass relation is obtained relating the pseudo-axion mass and top partner mass, serving as a crucial test of the SLH mechanism. I also propose a strategy of analyzing the fine-tuning problem consistent with the spirit of CEFT and apply it to the SLH. The scalar potential and fine-tuning analysis strategies investigated here should also be applicable to a wide class of Little Higgs and Twin Higgs models, which may reveal interesting relations as crucial tests of the related electroweak symmetry breaking mechanism and provide a new perspective on assessing their degree of fine-tuning.

 

Date/Place Apr. 17th (Tue.) 15:30-16:30 / H711
Name Yohei Ema (KEK)
Title Flaxion and its SUSY extension (Slides)
Abstract In this talk, we propose a minimal extension of the standard model which includes only one additional complex scalar field, flavon, with flavor-dependent global U(1) symmetry. It not only explains the hierarchical flavor structure in the quark and lepton sector (including neutrino sector), but also solves the strong CP problem by identifying the CP-odd component of the flavon as the QCD axion, which we call flaxion. Furthermore, the flaxion model solves the cosmological puzzles in the standard model, i.e., origin of dark matter, baryon asymmetry of the universe, and inflation. We also discuss a supersymmetric extension of this model, paying a particular attention to dynamics of an additional scalar flat direction in the early universe.

 

Date/Place Apr. 11th (Wed.) (Informal) 12:10 / H711
Name Ryo Nagai (Tohoku University)
Title Roles of perturbative unitarity in extended Higgs scenarios (Slides)
Abstract One of the important roles of the SM Higgs boson is to keep WW scattering amplitudes perturbatively unitary in high energy limit. However, once the Higgs coupling deviates from the SM prediction, the perturbative unitarity might be broken down at the certain energy scale. In order to maintain the perturbative unitarity with anomalous higgs coupling in high energy limit, we need new particle(s) whose couplings are tuned to cancel the bad behavior of WW scattering amplitudes. The required conditions are called “unitarity sum rules”. The sum rules tell us nontrivial relationship between the properties of new particles/phenomena and the low-energy observables such as the 125GeV signal strengths (coupling strengths). In this talk, we discuss the implications of the unitarity sum rules and apply the sum rules to investigate physics beyond the standard model.

 

Date/Place Apr. 4th (Wed.) (Informal) 14:30-15:30 / H711
Name Ryoutaro Watanabe (Montreal U.)
Title Does complete set of data still prefer the B anomalies?
Abstract In this talk, I will show my ongoing work regarding new physics to accommodate the anomalies in b -> s mu mu and b -> c tau nu which have been standing on these days. So far, there are many papers for this topic and they concluded that U1 (singlet vector type of) leptoquark could explain the two simultaneously. In our work, we put a complete set of observables relevant for the above explanation and gives a fit analysis. As a result, we see what kind of patterns of LQ couplings are favored, which could be a guideline when one constructs a UV completed model to accommodate the B anomalies.

 

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