458 research outputs found
Probing dark radiation with inflationary gravitational waves
Recent cosmological observations indicate the existence of extra light
species, i.e., dark radiation. In this paper we show that signatures of the
dark radiation are imprinted in the spectrum of inflationary gravitational
waves. If the dark radiation is produced by the decay of a massive particle,
high frequency mode of the gravitational waves are suppressed. In addition, due
to the effect of the anisotropic stress caused by the dark radiation, a dip in
the gravitational wave spectrum may show up at the frequency which enters the
horizon at the time of the dark radiation production. Once the gravitational
wave spectrum is experimentally studied in detail, we can infer the information
on how and when the dark radiation was produced in the Universe.Comment: 10 pages, 7 figures; added references, minor corrections; version to
appear in Phys.Rev.
AMS-02 Antiprotons from Annihilating or Decaying Dark Matter
Recently the AMS-02 experiment reported an excess of cosmic ray antiprotons
over the expected astrophysical background. We interpret the excess as a signal
from annihilating or decaying dark matter and find that the observed spectrum
is well fitted by adding contributions from the annihilation or decay of dark
matter with mass of O(TeV) or larger. Interestingly, Wino dark matter with mass
of around 3 TeV, whose thermal relic abundance is consistent with present dark
matter abundance, can explain the antiproton excess. We also discuss the
implications for the decaying gravitino dark matter with R-parity violation.Comment: 12 pages, 3 figure
Inflationary Gravitational Waves and the Evolution of the Early Universe
We study the effects of various phenomena which may have happened in the
early universe on the spectrum of inflationary gravitational waves. The
phenomena include phase transitions, entropy productions from non-relativistic
matter, the production of dark radiation, and decoupling of dark
matter/radiation from thermal bath. These events can create several
characteristic signatures in the inflationary gravitational wave spectrum,
which may be direct probes of the history of the early universe and the nature
of high-energy physics.Comment: 48 pages, 18 figures; minor correction
Can decaying particle explain cosmic infrared background excess?
Recently the CIBER experiment measured the diffuse cosmic infrared background
(CIB) flux and claimed an excess compared with integrated emission from
galaxies. We show that the CIB spectrum can be fitted by the additional photons
produced by the decay of a new particle. However, it also contributes too much
to the anisotropy of the CIB, which is in contradiction with the anisotropy
measurements by the CIBER and Hubble Space Telescope.Comment: 14 pages, 3 figure
Is cosmological constant screened in Liouville gravity with matter?
There has been a proposal that infrared quantum effects of massless
interacting field theories in de-Sitter space may provide time-dependent
screening of the cosmological constant. As a concrete model of the proposal, we
study the three loop corrections to the energy-momentum tensor of massless
theory in the background of classical Liouville gravity in
dimensional de-Sitter space. We find that the cosmological constant is
screened in sharp contrast to the massless theory in
dimensions due to the sign difference between the cosmological constant of the
Liouville gravity and that of the Einstein gravity. To argue for the robustness
of our prediction, we introduce the concept of time-dependent infrared
counter-terms and examine if they recover the de-Sitter invariance in the
theory in comparison with the Sine-Gordon model where it was
possible.Comment: 28 pages, 7 eps figure
Wino LSP detection in the light of recent Higgs searches at the LHC
Recent LHC data showed excesses of Higgs-like signals at the Higgs mass of
around 125GeV. This may indicate supersymmetric models with relatively heavy
scalar fermions to enhance the Higgs mass. The desired mass spectrum is
realized in the anomaly-mediated supersymmetry breaking model, in which the
Wino can naturally be the lightest superparticle (LSP). We discuss
possibilities for confirming such a scenario, particularly detecting signals
from Wino LSP at direct detection experiments, indirect searches at neutrino
telescopes and at the LHC.Comment: 15 pages, 3 figures; added reference
Subjective social status and trajectories of self-rated health status: a comparative analysis of Japan and the United States
[Background] Japanese society is more egalitarian than the United States as is reflected by the lower degree of prevalence of social inequalities in health. We examined whether subjective socioeconomic status is associated with different trajectories of self-rated health (SRH), and whether this relationship differs between the United States and Japan. [Methods] We analyzed the responses of 3968 Americans from the survey Midlife in the United States, 2004–06, and the responses of 989 Japanese from the survey Midlife in Japan, 2008. We conducted a multilevel analysis with three self-ratings of health (10 years ago, current and 10 years in the future) nested within individuals and nested within 10 levels of subjective social status. Age, sex, educational level and subjective financial situation were adjusted. [Results] After making statistical adjustments for confounding variables, respondents in Japan continued to report lower average levels of health. However, the rate of expected decline in SRH over the next decade was strongly socially patterned in the United States, whereas it was not in Japan. [Conclusion] The Japanese showed no disparity in the anticipated trajectory of SRH over time, whereas the Americans showed a strong social class gradient in future trajectories of SRH
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