23,081 research outputs found
Gravitational-Wave Fringes at LIGO: Detecting Compact Dark Matter by Gravitational Lensing
Utilizing gravitational-wave (GW) lensing opens a new way to understand the
small-scale structure of the universe. We show that, in spite of its coarse
angular resolution and short duration of observation, LIGO can detect the GW
lensing induced by compact structures, in particular by compact dark matter
(DM) or primordial black holes of , which remain
interesting DM candidates. The lensing is detected through GW frequency
chirping, creating the natural and rapid change of lensing patterns:
\emph{frequency-dependent amplification and modulation} of GW waveforms. As a
highest-frequency GW detector, LIGO is a unique GW lab to probe such light
compact DM. With the design sensitivity of Advanced LIGO, one-year observation
by three detectors can optimistically constrain the compact DM density fraction
to the level of a few percent.Comment: 6 pages, 5 figures, v2: published version, Fig.5 updated with Poisson
distribution, improved discussion on the optical dept
Magnetogenesis from a rotating scalar: \`a la scalar chiral magnetic effect
The chiral magnetic effect (CME) is a phenomenon in which an electric current
is induced parallel to an external magnetic field in the presence of chiral
asymmetry in a fermionic system. In this paper, we show that the electric
current induced by the dynamics of a pseudo-scalar field which anomalously
couples to electromagnetic fields can be interpreted as closely analogous to
the CME. In particular, the velocity of the pseudo-scalar field, which is the
phase of a complex scalar, indicates that the system carries a global U(1)
number asymmetry as the source of the induced current. We demonstrate that an
initial kick to the phase-field velocity and an anomalous coupling between the
phase-field and gauge fields are naturally provided, in a set-up such as the
Affleck-Dine mechanism. The resulting asymmetry carried by the Affleck-Dine
field can give rise to instability in the (electro)magnetic field. Cosmological
consequences of this mechanism are also investigated.Comment: 35 pages, 1 figure; v2: extended discussions, comments and references
added, matches version accepted for publication in JHE
Peccei-Quinn Relaxion
The relaxation mechanism, which solves the electroweak hierarchy problem
without relying on TeV scale new physics, crucially depends on how a
Higgs-dependent back-reaction potential is generated. In this paper, we suggest
a new scenario in which the scalar potential induced by the QCD anomaly is
responsible both for the relaxation mechanism and the Peccei-Quinn mechanism to
solve the strong CP problem. The key idea is to introduce the relaxion and the
QCD axion whose cosmic evolutions become quite different depending on an
inflaton-dependent scalar potential. Our scheme raises the cutoff scale of the
Higgs mass up to 10^7 GeV, and allows reheating temperature higher than the
electroweak scale as would be required for viable cosmology. In addition, the
QCD axion can account for the observed dark matter of the universe as produced
by the conventional misalignment mechanism. We also consider the possibility
that the couplings of the Standard Model depend on the inflaton and become
stronger during inflation. In this case, the relaxation can be implemented with
a sub-Planckian field excursion of the relaxion for a cutoff scale below 10
TeV.Comment: 14 pages, 1 figure; minor changes, accepted for publication in JHE
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