976 research outputs found
Killing the Straw Man: Does BICEP Prove Inflation at the GUT Scale?
The surprisingly large value of , the ratio of power in tensor to scalar
density perturbations in the CMB reported by the BICEP2 Collaboration, if
confirmed, provides strong evidence for Inflation at the GUT scale. While the
Inflationary signal remains the best motivated source, a large value of
alone would still allow for the possibility that a comparable gravitational
wave background might result from a self ordering scalar field (SOSF)
transition that takes place later at somewhat lower energy. We find that even
without detailed considerations of the predicted BICEP signature of such a
transition, simple existing limits on the isocurvature contribution to CMB
anisotropies would definitively rule out a contribution of more than to
,. We also present a general relation for the allowed fractional
SOSF contribution to as a function of the ultimate measured value of .
These results point strongly not only to an inflationary origin of the BICEP2
signal, if confirmed, but also to the fact that if the GUT scale is of order
then either the GUT transition happens before Inflation or the
Inflationary transition and the GUT transition must be one and the same.Comment: 3 pages 2 figures, accepted for publication in Physics Letters B .
Accepted version revised slightly in response to referee's comment
Probing the Gravitational Wave Signature from Cosmic Phase Transitions at Different Scales
We present a new signature by which to one could potentially discriminate
between a spectrum of gravitational radiation generated by a self-ordering
scalar field vs that of inflation, specifically a comparison of the magnitude
of a flat spectrum at frequencies probed by future direct detection experiments
to the magnitude of a possible polarization signal in the Cosmic Microwave
Background (CMB) radiation. In the process we clarify several issues related to
the proper calculation of such modes, focusing on the effect of
post-horizon-crossing evolution.Comment: 4 pages, Phys. Rev D version (revised in response to referee's
comments
Higgs seesaw mechanism as a source for dark energy
Motivated by the seesaw mechanism for neutrinos which naturally generates small neutrino masses, we explore how a small grand-unified-theory-scale mixing between the standard model Higgs boson and an otherwise massless hidden sector scalar can naturally
The Scientific Reach of Multi-Ton Scale Dark Matter Direct Detection Experiments
The next generation of large scale WIMP direct detection experiments have the
potential to go beyond the discovery phase and reveal detailed information
about both the particle physics and astrophysics of dark matter. We report here
on early results arising from the development of a detailed numerical code
modeling the proposed DARWIN detector, involving both liquid argon and xenon
targets. We incorporate realistic detector physics, particle physics and
astrophysical uncertainties and demonstrate to what extent two targets with
similar sensitivities can remove various degeneracies and allow a determination
of dark matter cross sections and masses while also probing rough aspects of
the dark matter phase space distribution. We find that, even assuming dominance
of spin-independent scattering, multi-ton scale experiments still have
degeneracies that depend sensitively on the dark matter mass, and on the
possibility of isospin violation and inelasticity in interactions. We find that
these experiments are best able to discriminate dark matter properties for dark
matter masses less than around 200 GeV. In addition, and somewhat surprisingly,
the use of two targets gives only a small improvement (aside from the advantage
of different systematics associated with any claimed signal) in the ability to
pin down dark matter parameters when compared with one target of larger
exposure.Comment: 23 pages; updated to match PRD versio
Recommended from our members
Role of angiopoietin-like protein 3 in sugar-induced dyslipidemia in rhesus macaques: suppression by fish oil or RNAi.
Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ∼30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques
- …