873 research outputs found
Higgs condensation as an unwanted curvaton
During inflation in the early universe, the Higgs field continuously acquires
long-wave quantum fluctuations. They accumulate to yield a non-vanishing value
with an exponentially large correlation length. We study consequences of such
Higgs condensations to show that, in inflation models where the universe is
reheated through gravitational particle production at the transition to the
kination regime, they not only contribute to reheat the universe but also act
as a curvaton. Unfortunately, however, for parameters of the Standard Model
Higgs field, this curvaton produces density fluctuations too large, so the
inflation models followed by a long kination regime are ruled out.Comment: 13 pages; v2, layout adjusted, references adde
Particle creation in a toroidal universe
We calculate the particle production rate in an expanding universe with a
three-torus topology. We discuss also the complete evolution of the size of
such a universe. The energy density of particles created through the nonzero
modes is computed for selected masses. The unique contribution of the zero mode
and its properties are also analyzed.Comment: 9 pages, 11 figure
Self-Energy Correction to the Two-Photon Decay Width in Hydrogenlike Atoms
We investigate the gauge invariance of the leading logarithmic radiative
correction to the two-photon decay width in hydrogenlike atoms. It is shown
that an effective treatment of the correction using a Lamb-shift "potential"
leads to equivalent results in both the length as well as the velocity gauges
provided all relevant correction terms are taken into account. Specifically,
the relevant radiative corrections are related to the energies that enter into
the propagator denominators, to the Hamiltonian, to the wave functions, and to
the energy conservation condition that holds between the two photons; the form
of all of these effects is different in the two gauges, but the final result is
shown to be gauge invariant, as it should be. Although the actual calculation
only involves integrations over nonrelativistic hydrogenic Green functions, the
derivation of the leading logarithmic correction can be regarded as slightly
more complex than that of other typical logarithmic terms. The dominant
radiative correction to the 2S two-photon decay width is found to be -2.020536
(alpha/pi) (Zalpha)^2 ln[(Zalpha)^-2] in units of the leading nonrelativistic
expression. This result is in agreement with a length-gauge calculation [S. G.
Karshenboim and V. G. Ivanov, e-print physics/9702027], where the coefficient
was given as -2.025(1).Comment: 9 pages, RevTe
How particle collisions increase the rate of accretion from the cosmological background onto primordial black holes in braneworld cosmology
It is shown that, contrary to the widespread opinion, particle collisions
considerably increase accretion rate from the cosmological background onto 5D
primordial black holes formed during the high-energy phase of the
Randall-Sundrum Type II braneworld scenario. Increase of accretion rate leads
to much tighter constraints on initial primordial black hole mass fraction
imposed by the critical density limit and measurements of high-energy diffuse
photon background and antiproton excess.Comment: 5 pages, 4 figure
Survival probability of a diffusing test particle in a system of coagulating and annihilating random walkers
We calculate the survival probability of a diffusing test particle in an
environment of diffusing particles that undergo coagulation at rate lambda_c
and annihilation at rate lambda_a. The test particle dies at rate lambda' on
coming into contact with the other particles. The survival probability decays
algebraically with time as t^{-theta}. The exponent theta in d<2 is calculated
using the perturbative renormalization group formalism as an expansion in
epsilon=2-d. It is shown to be universal, independent of lambda', and to depend
only on delta, the ratio of the diffusion constant of test particles to that of
the other particles, and on the ratio lambda_a/lambda_c. In two dimensions we
calculate the logarithmic corrections to the power law decay of the survival
probability. Surprisingly, the log corrections are non-universal. The one loop
answer for theta in one dimension obtained by setting epsilon=1 is compared
with existing exact solutions for special values of delta and
lambda_a/lambda_c. The analytical results for the logarithmic corrections are
verified by Monte Carlo simulations.Comment: 8 pages, 8 figure
CMB Neutrino Mass Bounds and Reionization
Current cosmic microwave background (CMB) bounds on the sum of the neutrino
masses assume a sudden reionization scenario described by a single parameter
that determines the onset of reionization. We investigate the bounds on the
neutrino mass in a more general reionization scenario based on a principal
component approach. We found the constraint on the sum of the neutrino masses
from CMB data can be relaxed by a 40% in a generalized reionization
scenario. Moreover, the amplitude of the r.m.s. mass fluctuations is
also considerably lower providing a better consistency with a low amplitude of
the Sunyaev-Zel'dovich signal
Time-reversal symmetric resolution of unity without background integrals in open quantum systems
We present a new complete set of states for a class of open quantum systems,
to be used in expansion of the Green's function and the time-evolution
operator. A remarkable feature of the complete set is that it observes
time-reversal symmetry in the sense that it contains decaying states (resonant
states) and growing states (anti-resonant states) parallelly. We can thereby
pinpoint the occurrence of the breaking of time-reversal symmetry at the choice
of whether we solve Schroedinger equation as an initial-condition problem or a
terminal-condition problem. Another feature of the complete set is that in the
subspace of the central scattering area of the system, it consists of
contributions of all states with point spectra but does not contain any
background integrals. In computing the time evolution, we can clearly see
contribution of which point spectrum produces which time dependence. In the
whole infinite state space, the complete set does contain an integral but it is
over unperturbed eigenstates of the environmental area of the system and hence
can be calculated analytically. We demonstrate the usefulness of the complete
set by computing explicitly the survival probability and the escaping
probability as well as the dynamics of wave packets. The origin of each term of
matrix elements is clear in our formulation, particularly the exponential
decays due to the resonance poles.Comment: 62 pages, 13 figure
Constraints On The Topology Of The Universe From The WMAP First-Year Sky Maps
We compute the covariance expected between the spherical harmonic
coefficients of the cosmic microwave temperature anisotropy if the
universe had a compact topology. For fundamental cell size smaller than the
distance to the decoupling surface, off-diagonal components carry more
information than the diagonal components (the power spectrum). We use a maximum
likelihood analysis to compare the Wilkinson Microwave Anisotropy Probe
first-year data to models with a cubic topology. The data are compatible with
finite flat topologies with fundamental domain times the distance to
the decoupling surface at 95% confidence. The WMAP data show reduced power at
the quadrupole and octopole, but do not show the correlations expected for a
compact topology and are indistinguishable from infinite models.Comment: 16 pages, 5 figure
Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with Fermi
Dwarf spheroidal galaxies are known to be excellent targets for the detection
of annihilating dark matter. We present new limits on the annihilation cross
section of Weakly Interacting Massive Particles (WIMPs) based on the joint
analysis of seven Milky Way dwarfs using a frequentist Neyman construction and
Pass 7 data from the Fermi Gamma-ray Space Telescope. We exclude generic WIMP
candidates annihilating into b-bbar with mass less than 40 GeV that reproduce
the observed relic abundance. To within 95% systematic errors on the dark
matter distribution within the dwarfs, the mass lower limit can be as low as 19
GeV or as high as 240 GeV. For annihilation into tau+tau- these limits become
19 GeV, 13 GeV, and 80 GeV respectively.Comment: 5 pages, 2 figures, 2 supplementary figure
Emission of Massive Scalar Fields by a Higher-Dimensional Rotating Black-Hole
We perform a comprehensive study of the emission of massive scalar fields by
a higher-dimensional, simply rotating black hole both in the bulk and on the
brane. We derive approximate, analytic results as well as exact numerical ones
for the absorption probability, and demonstrate that the two sets agree very
well in the low and intermediate-energy regime for scalar fields with mass
m_\Phi < 1 TeV in the bulk and m_\Phi < 0.5 TeV on the brane. The numerical
values of the absorption probability are then used to derive the Hawking
radiation power emission spectra in terms of the number of extra dimensions,
angular-momentum of the black hole and mass of the emitted field. We compute
the total emissivities in the bulk and on the brane, and demonstrate that,
although the brane channel remains the dominant one, the bulk-over-brane energy
ratio is considerably increased (up to 33%) when the mass of the emitted field
is taken into account.Comment: 28 pages, 18 figure
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