2,126 research outputs found
Large-scale magnetic fields, curvature fluctuations and the thermal history of the Universe
It is shown that gravitating magnetic fields affect the evolution of
curvature perturbations in a way that is reminiscent of a pristine
non-adiabatic pressure fluctuation. The gauge-invariant evolution of curvature
perturbations is used to constrain the magnetic power spectrum. Depending on
the essential features of the thermodynamic history of the Universe, the
explicit derivation of the bound is modified. The theoretical uncertainty in
the constraints on the magnetic energy spectrum is assessed by comparing the
results obtained in the case of the conventional thermal history with the
estimates stemming from less conventional (but phenomenologically allowed)
post-inflationary evolutions.Comment: 21 pages, 6 included figure
Pentaquark implications for exotic mesons
If the exotic baryon is a correlated with , then there should exist an exotic meson, GeV with width MeV. The
may be broad members of {\bf 10} \10bar in such a
picture. Vector mesons in the 1.4 - 1.7GeV mass range are also compared with
this picture
Lepton Flavor Violation without Supersymmetry
We study the lepton flavor violating (LFV) processes mu -> e gamma, mu -> 3e,
and mu -> e conversion in nuclei in the left-right symmetric model without
supersymmetry and perform the first complete computation of the LFV branching
ratios B(mu -> f) to leading non-trivial order in the ratio of left- and
right-handed symmetry breaking scales. To this order, B(mu -> e gamma) and B(mu
-> e) are governed by the same combination of LFV violating couplings, and
their ratio is naturally of order unity. We also find B(mu -> 3 e)/B(mu -> e)
\sim 100 under slightly stronger assumptions. Existing limits on the branching
ratios already substantially constrain mass splittings and/or mixings in the
heavy neutrino sector. When combined with future collider studies and precision
electroweak measurements, improved limits on LFV processes will test the
viability of low-scale, non-supersymmetric LFV scenarios.Comment: 24 pages, 7 figures, 2 table
Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler-broadening
We discuss a new solution of the Kompaneets-equation for physical situations
in which low frequency photons, forming relatively narrow spectral details, are
Compton scattered in an isotropic, infinite medium with an intense ambient
blackbody field that is very close to full thermodynamic equilibrium with the
free electrons. In this situation the background-induced stimulated Compton
scattering slows down the motion of photons toward higher frequencies by a
factor of 3 in comparison with the solution that only takes into account
Doppler-broadening and boosting. This new solution is important for detailed
computations of cosmic microwave background spectral distortions arising due to
uncompensated atomic transitions of hydrogen and helium in the early Universe.
In addition we derive another analytic solution that only includes the
background-induced stimulated Compton scattering and is valid for power-law
ambient radiation fields. This solution might have interesting applications for
radio lines arising inside of bright extra-galactic radio source, where
according to our estimates line shifts because of background-induced stimulated
scattering could be amplified and even exceed the line broadening due to the
Doppler-effect.Comment: 5 pages, 2 figures, submitted to A&
Macroscopic amplification of electroweak effects in molecular Bose-Einstein condensates
We investigate the possible use of Bose-Einstein condensates of diatomic
molecules to measure nuclear spin-dependent parity violation effects, outlining
a detection method based on the internal Josephson effect between molecular
states of opposite parity. When applied to molecular condensates, the fine
experimental control achieved in atomic bosonic Josephson junctions could
provide data on anapole moments and neutral weak couplings.Comment: 5 pages. To be published Phys. Rev. A (Rapid Communication) (2012
The Cosmological Evolution of Domain Wall Networks
We have studied the cosmological evolution of domain wall networks in two,
three and four spatial dimensions using high-resolution field theory
simulations. The dynamical range and number of our simulations is larger than
in previous works, but does not allow us to exclude previous hints of
deviations to the naively expected scale-invariant evolution. These results
therefore suggest that the approach of domain wall networks to linear scaling
is a much slower process than that of cosmic strings, which has been previously
characterized in detail.Comment: 7 pages, submitted to Phys Rev
Lyman alpha absorption lines from mini pancakes
[Abridged abstract:] Recent numerical simulations show that many \lyal
absorption lines of column densities \nha \la 10^{15} cm are produced
in transient, mini pancakes. Such pancakes are modeled here, approximating the
initial perturbation leading to the formation of the pancake as a single
sinusoidal wave. The density and temperature profiles of the gas in the pancake
are determined for , where is the collapse redshift. The
\lyal absorption line profiles for a line of sight through the pancake are
then calculated. The absorption lines in general have wings signifying bulk
motions in the gas. It is shown that the deviation from a single Voigt profile
is large for small H I column density lines, in which the effect of bulk
motions is large. For lines with \nha > 10^{13} cm, high temperature
tend to wash out the signatures of bulk motion. The analytical modeling of mini
pancakes associated with \lyal forest lines --- with 10^{13} \la \nha \la
10^{15} cm---gives the corresponding mass scales. It is shown here
that, for typical values of cosmological parameters, absorption lines with
\nha \sim 10^{14} cm correspond to structures with baryonic mass of
M with an overdensity of at .
The value of \nha can change by a factor in the course of evolution
of the pancake in time. It is also shown that there is an upper limit to \nha
from a pancake due to the slow recombination rate and the importance of
collisional ionization at high temperatures. Mini pancakes do not give rise to
\lyal lines with \nha \ga 10^{14.5} cm, for \j21=1 and
.Comment: Latex with aaspp4.sty (25 pages), 6 figures, Accepted for publication
in The Astrophysical Journa
Ab initio study of shock compressed oxygen
Quantum molecular dynamic simulations are introduced to study the shock
compressed oxygen. The principal Hugoniot points derived from the equation of
state agree well with the available experimental data. With the increase of
pressure, molecular dissociation is observed. Electron spin polarization
determines the electronic structure of the system under low pressure, while it
is suppressed around 30 50 GPa. Particularly, nonmetal-metal transition
is taken into account, which also occurs at about 30 50 GPa. In
addition, the optical properties of shock compressed oxygen are also discussed.Comment: 5 pages, 5 figure
Nucleation Rates of Water and Heavy Water using Equations of State
The original formula of Gibbs for the reversible work of critical nucleus formation is evaluated in three approximate ways for ordinary and heavy water. The least approximate way employs an equation of state to evaluate the pressure difference between the new and old phases. This form of the theory yields a temperature dependence for the nucleation rate close to that observed experimentally. This is a substantial improvement over the most commonly used (and most approximate) form of classical theory.©2004 American Institute of Physics
Cosmological Hysteresis and the Cyclic Universe
A Universe filled with a homogeneous scalar field exhibits `Cosmological
hysteresis'. Cosmological hysteresis is caused by the asymmetry in the equation
of state during expansion and contraction. This asymmetry results in the
formation of a hysteresis loop: , whose value can be non-vanishing
during each oscillatory cycle. For flat potentials, a negative value of the
hysteresis loop leads to the increase in amplitude of consecutive cycles and to
a universe with older and larger successive cycles. Such a universe appears to
possess an arrow of time even though entropy production is absent and all of
the equations respect time-reversal symmetry ! Cosmological hysteresis appears
to be widespread and exists for a large class of scalar field potentials and
mechanisms for making the universe bounce. For steep potentials, the value of
the hysteresis loop can be positive as well as negative. The expansion factor
in this case displays quasi-periodic behaviour in which successive cycles can
be both larger as well as smaller than previous ones. This quasi-regular
pattern resembles the phenomenon of BEATS displayed by acoustic systems.
Remarkably, the expression relating the increase/decrease in oscillatory cycles
to the quantum of hysteresis appears to be model independent. The cyclic
scenario is extended to spatially anisotropic models and it is shown that the
anisotropy density decreases during successive cycles if the hysteresis loop is
negative.Comment: 31 pages, 8 figures. Matches version published in Phys Rev D85,
123542 (2012
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