6,142 research outputs found
Cosmic evolution during primordial black hole evaporation
Primordial black holes with a narrow mass range are regarded as a
nonrelativistic fluid component with an equation of state for dust. The impact
of the black hole evaporation on the dynamics of the early universe is studied
by resorting to a two-fluid model. We find periods of intense radiation
reheating in the initial and final stages of the evaporation.Comment: 12 pages, Revtex, two figures, to appear in Phys.Rev.
Constraining interacting dark energy models with flux destabilization
A destabilization in the transfer energy flux from the vacuum to radiation,
for two vacuum decay laws relevant to the dark energy problem, is analyzed
using the Landau-Lifshitz fluctuation hydrodynamic theory. Assuming thermal (or
near thermal) equilibrium between the vacuum and radiation, at the earliest
epoch of the Universe expansion, we show that the law due to
renormalization-group running of the cosmological constant term, with
parameters chosen not to spoil the primordial nucleosynthesis scenario, does
soon drive the flux to fluctuate beyond its statistical average value thereby
distorting the cosmic background radiation spectrum beyond observational
limits. While the law coming from the saturated holographic dark energy does
not lead the flux to wildly fluctuate, a more realistic non--saturated form
shows again such anomalous behavior.Comment: 12 pages, minor correction, to appear in Physics Letters
Power Counting of Contact-Range Currents in Effective Field Theory
We analyze the power counting of two-body currents in nuclear effective field
theories (EFTs). We find that the existence of non-perturbative physics at low
energies, which is manifest in the existence of the deuteron and the 1S0 NN
virtual bound state, combined with the appearance of singular potentials in
versions of nuclear EFT that incorporate chiral symmetry, modifies the
renormalization-group flow of the couplings associated with contact operators
that involve nucleon-nucleon pairs and external fields. The order of these
couplings is thereby enhanced with respect to the naive-dimensional-analysis
estimate. Consequently, short-range currents enter at a lower order in the
chiral EFT than has been appreciated up until now, and their impact on
low-energy observables is concomitantly larger. We illustrate the changes in
the power counting with a few low-energy processes involving external probes
and the few-nucleon systems, including electron-deuteron elastic scattering and
radiative neutron capture by protons.Comment: 5 pages. Minor revisions. Conclusions unchanged. Version to appear in
Physical Review Letter
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