157 research outputs found

### Detecting Axion Stars with Radio Telescopes

When axion stars fly through an astrophysical magnetic background, the
axion-to-photon conversion may generate a large electromagnetic radiation
power. After including the interference effects of the spacially-extended
axion-star source and the macroscopic medium effects, we estimate the radiation
power when an axion star meets a neutron star. For a dense axion star with
$10^{-13}\,M_\odot$, the radiated power is at the order of
10^{11}\,\mbox{W}\times(100\,\mu\mbox{eV}/m_a)^4\,(B/10^{10}\,\mbox{Gauss})^2
with $m_a$ as the axion particle mass and $B$ the strength of the neutron star
magnetic field. For axion stars occupy a large fraction of dark matter energy
density, this encounter event with a transient \mathcal{O}(0.1\,\mbox{s})
radio signal may happen in our galaxy with the averaged source distance of one
kiloparsec. The predicted spectral flux density is at the order of $\mu$Jy for
a neutron star with $B\sim 10^{13}$ Gauss. The existing Arecibo, GBT, JVLA and
FAST and the ongoing SKA radio telescopes have excellent discovery potential of
dense axion stars.Comment: 16 pages, 2 figure

### Asymptotic safety of higher derivative quantum gravity non-minimally coupled with a matter system

We study asymptotic safety of models of the higher derivative quantum gravity
with and without matter. The beta functions are derived by utilizing the
functional renormalization group, and non-trivial fixed points are found. It
turns out that all couplings in gravity sector, namely the cosmological
constant, the Newton constant, and the $R^2$ and $R_{\mu\nu}^2$ coupling
constants, are relevant in case of higher derivative pure gravity. For the
Higgs-Yukawa model non-minimal coupled with higher derivative gravity, we find
a stable fixed point at which the scalar-quartic and the Yukawa coupling
constants become relevant. The relevant Yukawa coupling is crucial to realize
the finite value of the Yukawa coupling constants in the standard model.Comment: Version published in JHEP; 75 pages, 10 figures, typos corrected,
references adde

### Massive modes in magnetized brane models

We study higher dimensional models with magnetic fluxes, which can be derived
from superstring theory. We study mass spectrum and wavefunctions of massless
and massive modes for spinor, scalar and vector fields. We compute the 3-point
couplings and higher order couplings among massless modes and massive modes in
4D low-energy effective field theory. These couplings have non-trivial
behaviors, because wavefunctions of massless and massive modes are non-trivial.Comment: 21 page

### Weak Gravity Conjecture, Multiple Point Principle and the Standard Model Landscape

The requirement for an ultraviolet completable theory to be well-behaved upon
compactification has been suggested as a guiding principle for distinguishing
the landscape from the swampland. Motivated by the weak gravity conjecture and
the multiple point principle, we investigate the vacuum structure of the
standard model compactified on $S^1$ and $T^2$. The measured value of the Higgs
mass implies, in addition to the electroweak vacuum, the existence of a new
vacuum where the Higgs field value is around the Planck scale. We explore two-
and three-dimensional critical points of the moduli potential arising from
compactifications of the electroweak vacuum as well as this high scale vacuum,
in the presence of Majorana/Dirac neutrinos and/or axions. We point out
potential sources of instability for these lower dimensional critical points in
the standard model landscape. We also point out that a high scale $AdS_4$
vacuum of the Standard Model, if exists, would be at odd with the conjecture
that all non-supersymmetric $AdS$ vacua are unstable. We argue that, if we
require a degeneracy between three- and four-dimensional vacua as suggested by
the multiple point principle, the neutrinos are predicted to be Dirac, with the
mass of the lightest neutrino O(1-10) meV, which may be tested by future CMB,
large scale structure and $21$cm line observations.Comment: 56 pages, 22 figures, published versio

### Reheating-era leptogenesis

We propose a novel leptogenesis scenario at the reheating era. Our setup is
minimal in the sense that, in addition to the standard model Lagrangian, we
only consider an inflaton and higher dimensional operators. The lepton number
asymmetry is produced not by the decay of a heavy particle, but by the
scattering between the standard model particles. After the decay of an
inflaton, the model is described within the standard model with higher
dimensional operators. The Sakharov's three conditions are satisfied by the
following way. The violation of the lepton number is realized by the
dimension-5 operator. The complex phase comes from the dimension-6 four lepton
operator. The universe is out of equilibrium before the reheating is completed.
It is found that the successful baryogenesis is realized for the wide range of
parameters, the inflaton mass and reheating temperature, depending on the
cutoff scale. Since we only rely on the effective Lagrangian, our scenario can
be applicable to all mechanisms to generate neutrino Majorana masses.Comment: 5 pages, 3 figures; published version(v2

### Soft pion theorem, asymptotic symmetry and new memory effect

It is known that soft photon and graviton theorems can be regarded as the
Ward-Takahashi identities of asymptotic symmetries. In this paper, we consider
soft theorem for pions, i.e., Nambu-Goldstone bosons associated with a
spontaneously broken axial symmetry. The soft pion theorem is written as the
Ward-Takahashi identities of the $S$-matrix under asymptotic transformations.
We investigate the asymptotic dynamics, and find that the conservation of
charges generating the asymptotic transformations can be interpreted as a pion
memory effect.Comment: 25 pages, 2 figures, v2: references and discussions adde

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