Seminars in 2015

Seminars from April 2015 through March 2016.

QG Seminar

Title
Bigravity from gradient expansion
Speaker
Yasuho Yamashita ( YITP, Kyoto Univ.)
Date & Time
Thursday, February 25, 2016, 1:00 p.m.
Place
QG colloquim (ES744)
Abstract
In general, bigravity, i.e., the gravitational model that contains two gravitons interacting with each other, was known to be suffered from an unavoidable ghost mode, which is called Boulware-Deser (BD) ghost. Recently, however, the restriction of the interaction to the specific form of non-derivative coupling proposed by de Rham, Gabadadze and Tolley is found to evade the BD ghost problem. We discuss how this ghost free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization and obtain the effective four-dimensional action by solving the bulk configuration for given boundary metrics and substituting back the solution into the action under the gradient expansion. In the obtained effective theory, two gravitons interact through the Fierz-Pauli mass term and the radion remains as a scalar field, but its coupling to the metrics is non-trivial.

EHQG Seminar

Title
Lattice QCD approach to axion physics
Speaker
Norikazu Yamada ( KEK)
Date & Time
Tuesday, February 23, 2016, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Axion introduced to solve Strong CP problem is also a good candidate for dark matter, and QCD topological susceptibility, $\chi_t$, plays an central role in estimating the axion abundance. After explaining how $\chi_t(T)$ is estimated for now, I mention the current status of the lattice determinations of $\chi_t$ and the problem.

EHQG Seminar

Title
Entanglement Entropy of Two Black Holes and Entanglement Entropic Force
Speaker
Noburo Shiba ( YITP, Kyoto Univ.)
Date & Time
Tuesday, February 16, 2016, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Entanglement entropy (EE) in quantum field theory was originally studied to explain the black hole entropy. EE naturally arises when we consider the black hole because we cannot obtain the information in the black hole. In this work, we consider EE on the outside region of two black holes. The EE depends on the distance between two black holes. So, if we can consider the EE as thermodynamic entropy, we can see the entropic contribution for the force between black holes from the distance dependence of the EE. First we study EE and mutual information for two spatially disjoint regions in Minkowski spacetime. We guess the EE in two black hole case from the result in the EE in Minkowski spacetime.

EHQG Seminar

Title
Analytic solutions of relativistic hydrodynamics
Speaker
Yoshitaka Hatta ( YITP, Kyoto Univ.)
Date & Time
Tuesday, February 2, 2016, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Using conformal symmetry, I discuss various analytic solutions of relativistic viscous hydrodynamics. These include spherical and anisotropic solutions, rotating solutions and boost-invariant and non-boost-invariant solutions. Possible applications to the Quark Gluon Plasma in heavy-ion collisions are also discussed.

QG Seminar

Title
Probing Fundamental Physics with Universal Relations for Neutron Stars
Speaker
Kento Yagi ( Princeton Univ.)
Date & Time
Tuesday, January 26, 2016, 5:00 p.m.
Place
QG colloquim (ES744)
Abstract
Neutron stars offer us an excellent testbed to probe fundamental physics, such as nuclear physics and strong-field gravity. Unlike the well-studied mass-radius relation for neutron stars that depends strongly on their internal structure, I first report unexpected universal relations that we found among the moment of inertia, tidal Love number and quadrupole moment ("I-Love-Q" relations) that are insensitive to the internal structure. Such universal relations help us break the degeneracy among neutron star parameters when probing fundamental physics with radio, X-ray or gravitational wave observations. In the second part of my talk, I report another universal relations among tidal parameters in gravitational waves from neutron star binaries. Such relations have applications not only to gravitational wave astrophysics, but also to nuclear physics as they improve the measurement accuracy of tidal parameters. Moreover, the relations improve our ability to test extreme gravity and perform cosmology with gravitational waves emitted from neutron star binaries.

EHQG Seminar

Title
Statistics of Flux Vacua for Particle Physics
Speaker
Taizan Watari ( KIPMU, Univ.Tokyo)
Date & Time
Tuesday, January 19, 2016, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
String compactification admits large number of vacua, at least if we follow widely accepted understanding of string theory these days. This means that string theory has very little predictive power in determining the field theory model at low-energy, but we can still study statistics of observables in such a large ensemble of vacua obtained in string theory. That may be used to provide theoretical foundation for the notion of naturalness. This presentation will cover a recent progress (arXiv:1408.6156, 1408.6167 and 1506.08433) that is along the line of approach described above. Statistical distributions of the number of generations, rank of gauge group and U(1) symmetry breaking parameter will be discussed.

EHQG Seminar

Title
Gravitational scalar-tensor theory
Speaker
Atsushi Naruko ( Tokyo Institute of Technology)
Date & Time
Tuesday, January 12, 2016, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
We consider a new form of theories of gravity in which the action is written in terms of the Ricci scalar and its first and second derivatives. Despite the higher derivative nature of the action, the theory is free from ghost under an appropriate choice of the functional form of the Lagrangian. This model possesses 2 + 2 physical degrees of freedom, namely 2 scalar degrees and 2 tensor degrees. We also discuss the correspondence between these theories and generalized bi-Galileon theories.

QG Seminar

Title
Physics of Dissipation in Continuum Dynamics
Speaker
Shu-ichiro Inutsuka ( Nagoya Univ.(Ta Lab))
Date & Time
Monday, December 21, 2015, 3:30 p.m.
Place
QG colloquium (ES744)
Abstract
I will give concise reviews of two topics that might interest the QG Lab members. Part 1) Dissipation in Relativistic Hydrodynamics: Relativistic hydrodynamics is a useful framework for describing astrophysical phenomena around compact objects such as black holes and neutron stars. Dissipation is critical and unavoidable in time evolution and generally leads to thermalization. However, the useful and reliable framework for describing dissipation in relativistic theory is still missing. Recent progress in collider experiments of “quark-gluon plasma” sheds light on this issue and activates the theoretical research. I will explain the essence of difficulty and provide a convenient way to handle this. The direction for ultimate solution is also suggested. Part 2) Evolutionary Conditions for Magnetohydrodynamic Shocks: The evolutionary conditions of dissipative magneto-hydrodynamic (MHD) shocks are revisited. I will first explain the general concept of evolutionary condition and structural stability of a mathematical solution of the corresponding physics framework. The condition is essentially required for a solution to appear in reality, and can be used for examining the validity of each solution. In 2007 we tried to prove the evolutionary condition of MHD intermediate shocks that was supposed to be non-evolutionary. We modify our previous approach using causal theory of dissipation. Our results may prove that intermediate shocks may appear in reality, contrary to the conclusion in standard textbooks such as Landau-Lifshitz.

EHQG Seminar

Title
Tao Probing the End of the World
Speaker
MAsato Taki ( Riken)
Date & Time
Tuesday, December 15, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
After explaining basic background materials, I will introduce a new IIB 5-brane description for the 6d E-string theory which is the world-volume theory on M5-brane probing the end of the world M9-brane. The E-string in our new realization, which is named Tao web, is depicted as spiral 5-branes web equipped with the cyclic structure which is a key to uplifting to 6 dimensions. Utilizing the topological vertex to the 5-brane web configuration enables us to write down a combinatorial formula for the generating function of the E-string elliptic genera, namely the full partition function of topological strings on local 1/2 K3 surface.

EHQG Seminar

Title
Hadron Spectroscopy at J-PARC
Speaker
Hiroyuki Noumi ( RCNP, Osaka Univ.)
Date & Time
Tuesday, December 1, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
How are hadrons formed from quarks and gluons? This is a fundamental question in hadron physics. It is not straight-foward to answer the question. Due to non-perturbative nature of the strong interaction in low energy, it is still not easy to describe hadrons by directly solving the QCD equation. Then, a theoretical model of introducing effective building blocks of hadrons, such as the constituent quark model, rather reasonably well describe hadrons. This is good to see "picture" how hadrons are formed. But, the constituent quark model sometimes fails in excited states. In particular, so-called exotic hadrons, such as X, Y, Z, and pentaquark states in heavy flavor sector, cannot be explained by naive quark model. This suggests that more charactoristic quark correlations, such as diauqarks and/or hadrons, may play roles as effective degrees of freedom in describing excited hadrons. To reveal them, hadron spectroscopy to look into more details of internal structure or motions of the composites in hadrons is of importance. J-PARC deivers the world-highest intensity of hadron beams and provides unique experimental opportunities on hadron physics. I will introduce my current interest on spectroscopic study of excited hyperon below KbarN threshold and future plans on charmed baryon spectroscopy at J-PARC.

EHQG Seminar

Title
Electroweak symmetry breaking and cold dark matter from strongly interacting hidden sector
Speaker
Pyungwon Ko (KIAS)
Date & Time
Tuesday, November 24, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
In this talk, I describe a model for electroweak symmetry breaking and cold dark matter with QCD-like strongly interacting hidden sector with classical scale invariance. The lightest hidden sector mesons and baryons could be long-lived because the h-flavor and h-baryon numbers are accidental symmetries of h-QCD. All the mass scales including DM masses are generated by dimensional transmutation in the h-QCD.

EHQG Seminar

Title
Higher spin AdS_3 holography and superstring theory
Speaker
Yasuaki Hikida (Rikkyo Univ.)
Date & Time
Tuesday, November 17, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Higher spin gauge theory is expected to describe the tensionless limit of superstring theory, and it attracts a lot of attention due to the application for AdS/CFT correspondence. As examples, a 4d higher spin gauge theory is proposed to be dual to 3d O(N) vector model, and a 3d higher spin gauge theory is claimed to correspond to 2d large N minimal model. Recently, it becomes possible to discuss concrete relations between higher spin gauge theory and superstring theory by extending these dualities. In this talk, I will review recent developments particularly focusing on AdS_3 case, and our works on the extensions of duality and relations to superstring theory.

KMI/EHQG Seminar

Title
Resurrecting the minimal renormalizable supersymmetric SU(5) model
Speaker
Borut Bajc (IJS, Ljubljana, Slovenia)
Date & Time
Tuesday, November 10, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
It is a well-known fact that the minimal renormalizable supersymmetric SU(5) model is ruled out assuming superpartner masses of the order of a few TeV. Giving up this constraint and assuming only SU(5) boundary conditions for the soft terms, we find that the model is still alive. The viable region of the parameter space typically features super partner masses of order 10^2 to 10^4 TeV, with tan(beta) values between 2 and 5, but lighter spectra with single states around 10 TeV are also possible. The main constraints come from proton decay, the Higgs mass, the requirement of the SU(5) spectrum being reasonably below the Planck scale, and the lifetime of the universe. A generic feature of the model is metastability of the electroweak vacuum. In the absence of a suitable dark matter particle in the neutralino sector, a light (order GeV or smaller) gravitino is a natural candidate.

QG Seminar

Title
Cosmology and astrophysics in the bigravity theory
Speaker
Katsuki Aoki (Waseda Univ.)
Date & Time
Monday, November 9, 2015, 4:00 p.m.
Place
QG colloquium (ES744)
Abstract
The bigravity theory, which contains a massive spin-2 field as well as a massless spin-2 field, is attractive related to the discovery of dark energy and dark matter. We discuss the viability of the bigravity from both cosmological and astrophysical points of view. In the cosmology, although the early Universe suffers from the Higuchi-type ghost or the gradient instability against the linear perturbation, the instabilities can be resolved by taking into account nonlinear effects of the scalar graviton for an appropriate parameter space of coupling constants. On the other hand, a singular behavior of scalar graviton appears in a static compact object beyond a critical value of gravitational field strength in a parameter space. The maximum mass of the neutron star or the coupling constants of bigravity is constrained to evade the singular behavior.

Colloquium

Title
AdS時空の不安定性
Speaker
Akihiro Ishibashi (Kinki Univ.)
Date & Time
Thursday, November 5, 2015, 2:00 p.m.
Place
第6講義室 (A421)
Abstract

Special Lecture(for DC)

Title
高次元ブラックホール
Speaker
Akihiro Ishibashi (Kinki Univ.)
Date & Time
Wednesday, November 4–Friday, November 6, 2015
Place
第6講義室 (A421)
Abstract

EHQG Seminar

Title
The microstate geometry program - the past, present, and future
Speaker
Masaki Sigemori (YITP, Kyoto Univ.)
Date & Time
Tuesday, October 27, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Because the black hole has entropy proportional to its horizon area, it must represent a statistical mechanical ensemble of underlying microstates. The no-hair theorems of GR seem to imply that there cannot be any such microstates in gravity. However, for black holes that exist in string theory, many "microstate geometries", which have the same asymptotic charge as black holes and are horizonless and regular, have been explicitly constructed. The reasons why we can avoid no-hair theorems are (1) the solutions are in d>4 dimensions (2) they are solutions of supergravity with various matter fields and Chern-Simons interactions, and (3) they have non-trivial topology. I would like to review the "microstate geometry program" to construct such black hole microstates in the framework of classical supergravity by explaining its goal and achievements as well as problems and criticisms, and describe our recent work on the construction of a very general class of microstate geometries.

EHQG Seminar

Title
Primordial black hole formation from cosmological fluctuations
Speaker
Tomohiro Harada (Rikkyo Univ.)
Date & Time
Tuesday, October 20, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Primordial black holes are black holes which may have formed in the early universe and affected the subsequent evolution of the universe through Hawking radiation and as the source of gravitational field. To predict the abundance of primordial black hole formation for given cos- mological scenarios, it is essential to determine the formation threshold for primordial cosmological fluctuations, which are naturally described by cosmological long-wavelength solutions. After a brief introcution, I will talk the recent analytical and numerical results on the primordial black hole formation. This talk is based on our recent work [1, 2]. [1] T. Harada, C. M. Yoo, T. Nakama and Y. Koga, Phys. Rev. D 91 (2015) 8, 084057 [arXiv:1503.03934 [gr-qc]]. [2] T. Harada, C. M. Yoo and K. Kohri, Phys. Rev. D 88 (2013) 8, 084051 [Phys. Rev. D 89 (2014) 2, 029903] [arXiv:1309.4201 [astro-ph.CO]].

EHQG Seminar

Title
Gauge-Higgs Grand Unification
Speaker
Naoki Yamatsu (Osaka Univ.)
Date & Time
Tuesday, October 13, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
It is known that in principle a concept of grand unification can unify three gauge fields and five fermion fields of the Standard Model, respectively, and that of gauge-Higgs unification can unify gauge and scalar fields. It is expected that gauge-Higgs grand unification, which integrates the above two concepts, has their features. In this talk, after I give a quick review of grand unification, I will show which Lie groups are applicable to gauge-Higgs grand unification. As an example, I will discuss a gauge-Higgs grand unified model based on an SO(11) Lie group.

EHQG KMI Seminar

Title
Electron-Ion Collider: The Ultimate Electron Microscope
Speaker
Berndt Mueller (Duke University /Brookhaven National Laboratory)
Date & Time
Tuesday, October 6, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
In our everyday world, "glue", the gauge field responsible for the strong interaction, hides inside protons and neutrons. While its properties are formally encoded in the theory of quantum chromodynamics (QCD), many phenomenological aspects of its dynamics are still unexplored or poorly understood. How do gluons conspire to confine Quarks inside hadrons? What does gluon blackbody radiation look like? How do gluons generate 99 percent of the visible mass of the universe? Is there a limit to the packing density of gluons? I will briefly discuss what we know about the answers to these questions, and how they can be studied at the next generation of particle accelerators.

KMI/EHQG joint Seminar

Title
Scaling laws for thermo-electric transport at quantum criticality
Speaker
Andreas KARCH (University of Washington)
Date & Time
Tuesday, July 14, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Transport properties at quantum critical points are strongly constrained by dimensional analysis. They are typically governed by two critical exponents: the dynamical critical exponent z determining the relative scaling of spatial and temporal coordinates and the hyperscaling violating exponent theta. We will show that in general response to electromagnetic fields requires a third exponent, an anomalous dimension for the coupling to background fields. We show that this exponent is generically non-zero in critical points constructed via holography and discuss its potential relevance to the physics of cuprates.

EHQG Seminar

Title
Accretion of dark matter particles, formation of a mini-black hole and emission of gravitational waves
Speaker
Yasunari Kurita (Kanagawa Institute of Technology)
Date & Time
Tuesday, July 7, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Recently, it has been argued that many dark matter particles are accumulated in a star, eventually self gravitating and collapsing to form a mini black hole. The black hole will grow and destroy the host star. In previous studies, main motivation of considering this scenario is to give a constraint on the WIMP–nucleon cross section. In this talk, however, we focus attention on gravitational phenomena such as mini black hole formations and gravitational wave emission. We consider accretion of fermionic dark matter on a sun-like star and give a brief estimate of the amplitude and characteristic spacetime strain of the gravitational wave from the gravitational collapse.

EHQG Seminar

Title
Towards realistic models in SO(32) heterotic string theory
Speaker
Tatsuo Kobayash (Hokkaido Univ.)
Date & Time
Tuesday, June 30, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
We study model construction towards realistic models within the framework of SO(32) heterotic string theory. We consider torus compactification with magnetic fluxes. Then, we construct the models, which has the gauge group including SU(3)xSU(2)xU(1) and three chiral generations of quarks and leptons. We also study the gauge coupling unification.

QG-lecture

Title
Quantum Information and Black Hole Physics
Speaker
Masahiro Hotta (Tohoku Univ.)
Date & Time
Thursday, June 25–Friday, June 26, 2015
Place
6/25:ES035, 6/26:ES635

EHQG Seminar

Title
Generalization of the Nambu-Goldstone theorem
Speaker
Yoshimasa Hidaka (RIKEN)
Date & Time
Tuesday, June 23, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Symmetry and its spontaneous breaking are of basic importance for understanding the low energy physics in many-body systems. When a continuum symmetry is spontaneously broken, there appears a zero mode called Nambu-Goldstone (NG) mode, whose theory is well developed in Lorentz invariant systems. In contrast, in non-Lorentz invariant systems, the NG theorem has not been well developed. In this talk, we discuss the recent progress in generalization of NG theorem in non-Lorentz invariant systems. We also discuss the spontaneous breaking of space-time symmetries.

EHQG Seminar

Title
Integrability of cohomogeneity-one Nambu-Goto strings in maximally symmetric spaces
Speaker
Hideki Ishihara (Osaka City Univ.)
Date & Time
Tuesday, June 16, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
We consider an orbit space of the isometry group action generated by a Killing vector on a space, and introduce a metric that is weighted by the norm of the Killing vector. In the case of n-dimensional sphere, we classify the orbit spaces, and show the Hamiltonian system of the geodesic on the all orbit spaces are integrable in the Liouville sense, i.e., there exists n Poisson commuting invariants, with the help of the existence of Killing tensors. On a view point of physics, it suggests that the cohomogeneity-one Nambu-Goto strings in (anti-) de Sitter space are integrable.

EHQG Seminar

Title
A conjecture for black hole microstates and its application to the gauge/gravity correspondence
Speaker
Takeshi Morita (Shizuoka Univ.)
Date & Time
Tuesday, June 9, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
I introduce our proposal "p-soup conjecture" which explains the microscopic origin of thermodynamics of a certain class of black holes. By applying this proposal to the gauge/gravity correspondence, I show the mechanism that supersymmetric gauge theories exhibt black hole natures at strong coupling through a gauge theory analysis. Especially it naturally explains the origin of free energies of ABJM and 6d SCFT which are proportional to N^3/2 and N^3 respectively.

EHQG Seminar

Title
QCD phase transition at real chemical potential with canonical approach
Speaker
Yusuke Taniguchi (Tsukuba Univ.)
Date & Time
Tuesday, June 2, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
We study the finite density phase transition in the lattice QCD at real chemical potential. We adopt canonical approach and the canonical partition function is constructed for Nf=2 QCD. After derivation of the canonical partition function we calculate observables like the pressure, the quark number density, its second cumulant and the chiral condensate as a function of the real chemical potential. We covered a wide range of temperature region starting from the confining low to the deconfining high temperature. We observe signals for the deconfinement and the chiral restoration phase transition at real chemical potential below Tc starting from the confining phase.

QG Seminar

Title
CMB bispectrum.
Speaker
Takashi Hiramatsu (YITP, Kyoto Univ.)
Date & Time
Monday, June 1, 2015, 4:00 p.m.
Place
QG-Lab Colloquium Room (ES744)
Abstract
Cosmic Microwave Background (CMB) is known as a remnant of Big-Bang, and lots of past works in cosmology have paid attention to its potential to prove the very early Universe, even the issues regarding the birth of the Universe. In these days, our interests reached to so fine structures of the Universe, for instance, the statistical properties of the primordial fluctuations constructing the large-scale structure, and we can actually investigate them thanks to rapid and sophisticated development of observational technologies. In this talk, we focus on the bispectrum (three-point correlation function of the fluctuations) of CMB temperature fluctuations, which quantifies the non-Gaussian feature of the fluctuations. One of its origins is primordial, or inflation. The primordial non-Gaussianity plays important role to discriminate quite a lot of viable inflation models. The other is non-linear origin. The non-linear evolution of fluctuations also induces the non-Gaussianity, resulting in the non-trivial bispectrum. Unless we identify the latter contribution correctly, we cannot predict the significance of the primordial non-Gaussianity. To do it, we developed a new Boltzmann solver for CMB and a novel formulation to compute the dominant contribution of the bispectrum of the non-linear origin. We introduce them and present the up-to-date numerical results of the CMB bispectrum

EHQG Seminar

Title
Discrimination of the origin of the primordial perturbation.
Speaker
Teruaki Suyama (RESCEU)
Date & Time
Tuesday, May 12, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
All the cosmic structures in the Universe are descendents of the primordial perturbation. Recent cosmological observations strongly support the idea that the primordial perturbation is a direct consequence of vacuum fluctuations generated during inflation. However, detailed mechanism of how this was achieved remains elusive. In particular, we do not know whether the primordial perturbation comes from the same source as what caused inflation or not. In my talk, I consider the possibility of testing it by observations. After introducing basics of inflation, I will discuss what kinds of observables are suitable for this purpose and their status in comparison with current/future observations.

QG Seminar

Title
The firewall argument and discussion on black hoke quantum mechanics.
Speaker
Norihiro Iizuka (Osaka Univ.)
Date & Time
Monday, May 11, 2015, 4:00 p.m.
Place
QG-Lab Colloquium Room (ES744)
Abstract
I will review the firewall argument and black hole quantum mechanics.

EHQG Seminar

Title
Ramond-Ramond couplings of D-branes
Speaker
Seiji Terashima (YITP, Kyoto Univ.)
Date & Time
Tuesday, April 28, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Applying supersymmetric localization for superstring worldsheet theory with N=(1,1) supersymmetries on a cylinder and with arbitrary boundary interactions, we find the most general formula for the Ramond-Ramond (RR) coupling of D-branes. We allow all massive excitations of open superstrings, and find that only a finite number of them can contribute to the formula. The formula is written by Quillen's superconnection which includes higher form gauge fields, and the resultant general Chern-Simons terms are consistent with RR charge quantization. Applying the formula to boundary string field theory of a BPS D9-brane or a D9-antiD9 brane system, we find that any D9-brane creation via massive mode condensation is impossible.

EHQG Seminar

Title
Crystalline chiral condensates in dense QCD
Speaker
Hiroaki Abuki (Aichi University of Education)
Date & Time
Tuesday, April 21, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
The chiral condensate may develop a spatial structure at finite quark number density. In this talk, I will first present how this is possible, and then report on the analyses of quark matter phase diagram near the chiral critical point based on a systematic generalized Ginzburg-Landau approach. A particular focus will be put on the effect of isospin mismatch which makes a crystalline pion condensate show up at moderate density side.

EHQG Seminar

Title
Grand Unification and Subcritical Hybrid Inflation
Speaker
Koji Ishikawa (Kanazawa Univ.)
Date & Time
Tuesday, April 14, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
We consider hybrid inflation for small couplings of the inflaton to matter such that the critical value of the inflaton field exceeds the Planck mass. The effective inflaton potential interpolates between a quadratic potential at small field values and a plateau at large field values. Using the range for the scalar spectral index n_s and tensor-to-scalar ratio r favored by the Planck data, we find that the energy scale of the plateau is constrained to the interval (1.6 - 2.4) * 10^16 GeV which includes the energy scale of gauge coupling unification in the supersymmetric standard model. The tensor-to-scalar ratio is predicted to have the lower bound r > 0.049 for 60 e-folds before the end of inflation.

EHQG Seminar

Title
Cosmic strings and their future detectability
Speaker
Daisuke Yamauchi (Tokyo Univ.)
Date & Time
Tuesday, April 7, 2015, 5:00 p.m.
Place
Science Symposia (ES635)
Abstract
Cosmic strings are line-like objects that may have formed in the early Universe during symmery breaking phase transitions or at the end of inflation but do not dominate the subsequent Universe due to their late-time evolution. The presence of cosmic strings would leave a variety of traces such as the gravitational waves or the cosmic microwave background anisotropies without overclosing the Universe, which gives us rich information about the high energy physics. In this talk, I will present basis properties of the cosmic strings for non-experts. Then I would like to discuss the detectability of cosmic strings from future experiments. The various properties of the evolution of the string network is also discussed.