UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker1: Eugeny Babichev (Laboratoire de Physique Théorique d'Orsay)

Title: Caustic free completion of k-essence

Abstract:

Both k-essence and the pressureless perfect fluid develop caustic

singularities at finite time. We explore the connection between the two

and show that they belong to the same class of models, which admits the

caustic free completion by means of the canonical complex scalar field.

Specifically, the free massive/self-interacting complex scalar

reproduces dynamics of pressureless perfect fluid/shift-symmetric

k-essence under certain initial conditions in the limit of large

mass/sharp self-interacting potential. We elucidate a mechanism of

resolving caustic singularities in the complete picture.

Speaker2: Eung Jin Chun (KIAS)

Title: Dark matter in Supersymmetric Axion Models

Abstract:

The strong CP problem is nicely resolved by the Peccei-Quinn mechanism which

predicts a light pseudo-Goldstone boson, the axion. It is a dark matter

candidate whose abundance is produced through the misalignment. In

supersymmetric theories, the fermionic partner of the axion, the axino,

is another dark matter candidate and can alter the standard features of a

neutralino dark matter candidate. In this talk, we discuss cosmological

and phenomenological properties of the axion supermultiplet and its impact on

the dark matter physics.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Teruaki Suyama (RESCEU)

On a paper

JCAP 1402 (2014) 019 (arXiv:1309.5888)

"Pulsar timing signal from ultralight scalar dark matter"

Andrei Khmelnitsky, Valery Rubakov.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Shun-Pei Miao (National Cheng Kung Univ.) **[from 1:30 PM]**

Title: Deducing Cosmological Observables from the S-matrix

Abstract:

We study one loop quantum gravitational corrections to the long range force induced by the exchange of a massless scalar between two massive scalars. The various diagrams contributing to the flat space S-matrix are evaluated in a general covariant gauge and we show that dependence on the gauge parameters cancels at a point considerably *before* forming the full S-matrix, which is unobservable in cosmology. It is possible to interpret our computation as a solution to the effective field equations --- which could be done even in cosmology --- but taking account of quantum gravitational corrections from the source and from the observer.

UTAPwiki/セミナー/初期宇宙・相対論速報

No seminar due to CosPA2017

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Keisuke Inomata (ICRR)

Title: Double Inflation as a single origin of PBHs for all dark matter and LIGO

Abstract:

Primordial Black Hole (PBH) is one of the leading non-particle candidates

for dark matter (DM).

Although several observations severely constrain the amount of PBHs,

it is recently pointed out that there is an uncertainty on the microlensing constraints

below ~ 10^{-10} M_\odot which was ignored originally

but may weaken the constraints significantly.

In the seminar, facing this uncertainty, we investigate the possibility that

PBHs can make up all DM in a broad mass spectrum.

Moreover, we propose a concrete inflation model which can simultaneously produce

PBHs for all DM in a broad mass spectrum around O(10^{-13}) M_\odot

and PBHs for LIGO events in a sharp mass spectrum at O(10) M_\odot.

This talk is based on our recent paper (arXiv:1711.06129).

UTAPwiki/セミナー/初期宇宙・相対論速報

No seminar due to JGRG27

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Toyokazu Sekiguchi (RESCEU)

Title: Abundance of dark matter axion in the coupling with dark photon

Abstract:

The axion and axion-like particles originate from a variety of UV theories based on QFT as well as string theory. Couplings of those axions with U(1) gauge fields are fairly ubiquitous. They are known to offer rich phenomenology in the very early Universe, for instance, inflation and preheating. In my talk I’m going to focus on their effects on the abundance of the QCD axion produced from the misalignment mechanism. It is recently argued that the coupling of the axion to a hidden U(1) field suppresses the axion abundance, which can open up the axion window up to the GUT scale. The claim postulates that production of the axion fluctuations is negligible. We revisit the argument by performing 3d lattice simulations of the axion electrodynamics, where the nonlinear dynamics in the coevolution of the axion fluctuations and gauge field is incorporated to the full extent. We show production of the axion fluctuations plays a crucial role and the suppression is moderated significantly.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Louis Yang (IPMU)

Title: Postinflationary Higgs Relaxation and Leptogenesis

Abstract:

The discovery of the Higgs boson with a mass of 125 GeV implies a relatively slow rise of the Standard Model Higgs potential at large energy scales. A scalar field with such a shallow potential can develop a large vacuum expectation value (VEV) during inflation through quantum fluctuation. The relaxation of the large VEV of the Higgs field after inflation may play an important role in the early stage of the universe. In this talk, I will talk about the generation of large Higgs VEV and how to do leptogenesis using the postinflationary relaxation of the Higgs field. I will also discuss one observable consequence of this relaxation leptogenesis model, which could explain the excess found in the cosmic infrared background (CIB) radiation anisotropy.

UTAPwiki/セミナー/初期宇宙・相対論速報

Joint seminar at IPMU

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker1: Masaki Yamada (Tufts Univ.)

Title: On false vacuum decay catalyzed by black holes

Abstract:

False vacuum states are metastable in quantum field theories, and true vacuum bubbles can be nucleated due to the quantum tunneling effect. It was recently suggested that an evaporating Black Hole (BH) can be a catalyst of bubble nucleations and dramatically shortens the lifetime of the false vacuum. In particular, in the context of the Standard Model valid up to a certain energy scale, even a single evaporating BH may spoil the successful cosmology by inducing the decay of our electroweak vacuum. In this talk, we reinterpret catalyzed vacuum decay by BHs, using an effective action for a thin-wall bubble around a BH to clarify the meaning of bounce solutions. We calculate bounce solutions in the limit of a flat spacetime and in the limit of negligible backreaction to the metric, where it is much easier to understand the physical meaning, and compare these results with the full calculations done in the literature. As a result, we give a physical interpretation of the enhancement factor: it is nothing but the probability of producing states with a finite energy. This makes it clear that all the other states such as plasma should also be generated through the same mechanism, and calls for finite density corrections to the tunneling rate which tend to stabilize the false vacuum.

Speaker2: Ayuki Kamada (IBS)

Title: Galactic Rotation Curves with Dark Matter Self-Interactions

Abstract:

It has been shown that the LambdaCDM model can successfully explain large-scale structure of the universe. But it is not clear that it can accommodate observations on (sub-)galactic scales. In fact, the LambdaCDM model predicts dark matter halos, which are systematically denser than inferred from astrophysical observations. One interesting alternative assumes that dark matter particles are strongly interacting with each other. Dark matter self-interactions will lead to heat transfer from the hotter outer region to the cold inner region, reducing the central dark matter density. In this talk, I will show that the observed rotation curves of spiral galaxies are consistent with predicted in the SIDM model. I will also emphasize the importance of the baryonic disk in determining the SIDM halo profile.

UTAPwiki/セミナー/初期宇宙・相対論速報

Joint seminar at IPMU -> postponed to 11/6 due to a typhoon

UTAPwiki/セミナー/初期宇宙・相対論速報

No seminar due to Kavli IPMU 10th anniversary symposium

UTAPwiki/セミナー/初期宇宙・相対論速報

Holiday

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Jun'ichi Yokoyama (RESCEU)

Title: Spontaneous genesis after G-inflation

Abstract:

In kinetically driven G-inflation, the Universe after inflation

is dominated by the kinetic energy density of a free scalar field

whose energy density is dissipated in proportion to $a^{-6}$

so that the cosmic expansion law is like $a(t) \propto t^{1/3}$.

The reheating is achieved by gravitational particle production

or through direct coupling preserving the shift symmetry of the

model. We discuss spontaneous baryogenesis and asymmetric

dark matter genesis may be possible if these charge densities

have a derivative coupling with the inflaton.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Yuichiro Tada (IAP)

Title: Stochastic Formalism in Curved Field Space

Abstract:

In multi-field inflation scenarios, the scalar fields can span curved field spaces in general.

Recently it was pointed out that the sufficiently large field curvature can make the entropic

degrees of freedom tachyonic during inflation and alter the inflation dynamics [PRL117, 141301].

This geometrical destabilization can be applied to a large class of inflationary models.

To analyze the destabilization, we formalize the stochastic approach in the general curved

field space from first principles.

Also I’ll briefly mention the slow-roll phase well after the geometrical destabilization.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Katsuki Aoki (Waseda Univ.)

Title: condensate of massive graviton as dark matter

Abstract:

We study coherently oscillating massive gravitons in the ghost-free bigravity theory. This coherent field could be interpreted as a "condensate" of the massive gravitons, or it is regarded as a spacetime anisotropy from the geometrical point of view. We present that the condensate of massive graviton (or the spacetime anisotropy) is a viable candidate for dark matter. We also discuss a production of the spacetime anisotropy and find that the extragalactic magnetic field of a primordial origin can yield a sufficient amount of dark matter.

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Hiroaki Tahara (RESCEU) **[from 1PM]**

Title: Anisotropic inflation with the generalized G-inflation

Abstract:

I give a talk about our ongoing work on anisotropic inflation.

First, I review [1] which proves that homogeneous universes with

a positive cosmological constant evolve toward the de Sitter solution.

Next, I show that some classes of the generalized Galileon theories

cause anisotropic inflation. The anisotropic inflation can change the

background action dramatically, and I argue its application.

[1] Robert M. Wald, Phys. Rev. D 28(1983), 2118(R)

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Atsuhisa Ota (Tokyo Tech)

Title: Secondary isocurvature perturbations from acoustic reheating

Abstract:

We discuss the secondary isocurvature perturbations from mode coupling

effects called acoustic reheating in the Thomson scattering dominant

universe. The perfect fluid approximation for the photon energy

momentum tensor is invalid deep inside the horizon so that shear

viscosity and thermal conduction occur. They produce the deviations

from the ideal Planck distribution, which can be recast into the entropy

perturbation on superhorizon scales. We also show that the latter effect breaks the

conservation law for the photon energy momentum tensor because

there exists heat conduction from the baryon sector. Therefore, the

superhorizon isocurvature perturbations are generated at second

order.

#This seminar is based on our recent work; arXiv:1705.05196.

UTAPwiki/セミナー/初期宇宙・相対論速報

Joint seminar at RESCEU

Speaker1: Soichiro Morisaki [14:00- @ science building 4, #1116]

Speaker2: Leo Tsukada [15:00- @ science building 4, #1116]

Speaker3: Misao Sasaki [16:15- @ **science building 1, #233**]

(The third talk by Misao Sasaki doubles as RESCEU colloquium)

UTAPwiki/セミナー/初期宇宙・相対論速報

Speaker: Rampei Kimura (Tokyo Tech)

Title : Field theoretical extension of higher derivative fermionic theory

Abstract:

Next Monday, I will talk about our ongoing work : higher derivative fermionic field theory.

I will first give a brief introduction of the Grassmann algebra

and a fermionic version of Ostrogradsky’s ghost, based on arXiv:1704.02717.

Then I will introduce multiple scalar fields and Weyl fermion

to construct a field theoretical extension of the previous work

and derive sufficient (degeneracy) conditions to have an appropriate number of degrees of freedom

for avoiding Ostrogradsky’s ghost. I will give a successful model,

and the consistency between Hamiltonian and Lagrange formulation will be discussed as well.