1,080 research outputs found
On the difference between proton and neutron spin-orbit splittings in nuclei
The latest experimental data on nuclei at Sn permit us for the first
time to determine the spin-orbit splittings of neutrons and protons in
identical orbits in this neutron-rich doubly-magic region and compare the case
to that of Pb. Using the new results, which are now consistent for the
two neutron-rich doubly magic regions, a theoretical analysis defines the
isotopic dependence of the mean field spin-orbit potential and leads to a
simple explicit expression for the difference between the spin-orbit splittings
of neutrons and protons. The isotopic dependence is explained in the framework
of different theoretical approaches.Comment: 8 pages, revte
Cosmological evolution of warm dark matter fluctuations II: Solution from small to large scales and keV sterile neutrinos
We solve the cosmological evolution of warm dark matter (WDM) density
fluctuations with the Volterra integral equations of paper I. In the absence of
neutrinos, the anisotropic stress vanishes and the Volterra equations reduce to
a single integral equation. We solve numerically this equation both for DM
fermions decoupling at equilibrium and DM sterile neutrinos decoupling out of
equilibrium. We give the exact analytic solution for the density fluctuations
and gravitational potential at zero wavenumber. We compute the density contrast
as a function of the scale factor a for a wide range of wavenumbers k. At fixed
a, the density contrast grows with k for k
k_c, (k_c ~ 1.6/Mpc). The density contrast depends on k and a mainly through
the product k a exhibiting a self-similar behavior. Our numerical density
contrast for small k gently approaches our analytic solution for k = 0. For
fixed k < 1/(60 kpc), the density contrast generically grows with a while for k
> 1/(60 kpc) it exhibits oscillations since the RD era which become stronger as
k grows. We compute the transfer function of the density contrast for thermal
fermions and for sterile neutrinos in: a) the Dodelson-Widrow (DW) model and b)
in a model with sterile neutrinos produced by a scalar particle decay. The
transfer function grows with k for small k and then decreases after reaching a
maximum at k = k_c reflecting the time evolution of the density contrast. The
integral kernels in the Volterra equations are nonlocal in time and their
falloff determine the memory of the past evolution since decoupling. This
falloff is faster when DM decouples at equilibrium than when it decouples out
of equilibrium. Although neutrinos and photons can be neglected in the MD era,
they contribute in the MD era through their memory from the RD era.Comment: 27 pages, 6 figures. To appear in Phys Rev
String Tension and the Generation of the Conformal Anomaly
The origin of the string conformal anomaly is studied in detail. We use a
reformulated string Lagrangian which allows to consider the string tension
as a small perturbation. The expansion parameter is the worldsheet
speed of light c, which is proportional to . We examine carefully the
interplay between a null (tensionless) string and a tensionful string which
includes orders and higher. The conformal algebra generated by the
constraints is considered. At the quantum level the normal ordering provides a
central charge proportional to . Thus it is clear that quantum null
strings respect conformal invariance and it is the string tension which
generates the conformal anomaly.Comment: More references are included. Final version, to appear in Phys.Rev.D.
6 pages, LaTex, no figure
On the isospin dependence of the mean spin-orbit field in nuclei
By the use of the latest experimental data on the spectra of Sb and
Sn and on the analysis of properties of other odd nuclei adjacent to
doubly magic closed shells the isospin dependence of a mean spin-orbit
potential is defined. Such a dependence received the explanation in the
framework of different theoretical approaches.Comment: 52 pages, Revtex, no figure
Chaotic dynamics in preheating after inflation
We study chaotic dynamics in preheating after inflation in which an inflaton
is coupled to another scalar field through an interaction
. We first estimate the size of the quasi-homogeneous
field at the beginning of reheating for large-field inflaton potentials
by evaluating the amplitude of the fluctuations on
scales larger than the Hubble radius at the end of inflation. Parametric
excitations of the field during preheating can give rise to chaos
between two dynamical scalar fields. For the quartic potential (,
) chaos actually occurs for in a
linear regime before which the backreaction of created particles becomes
important. This analysis is supported by several different criteria for the
existence of chaos. For the quadratic potential () the signature of chaos
is not found by the time at which the backreaction begins to work, similar to
the case of the quartic potential with .Comment: 12 pages, 10 figures, Version to appear in Classical and Quantum
Gravit
Strings Near a Rindler Or Black Hole Horizon
Orbifold techniques are used to study bosonic, type II and heterotic strings
in Rindler space at integer multiples N of the Rindler temperature, and near a
black hole horizon at integer multiples of the Hawking temperature, extending
earlier results of Dabholkar. It is argued that a Hagedorn transition occurs
nears the horizon for all N>1.Comment: 13 pages, harvmac, (references added
Cosmological evolution of warm dark matter fluctuations I: Efficient computational framework with Volterra integral equations
We study the complete cosmological evolution of dark matter (DM) density
fluctuations for DM particles that decoupled being ultrarelativistic during the
radiation dominated era which is the case of keV scale warm DM (WDM). The new
framework presented here can be applied to other types of DM and in particular
we extend it to cold DM (CDM). The collisionless and linearized
Boltzmann-Vlasov equations (B-V) for WDM and neutrinos in the presence of
photons and coupled to the linearized Einstein equations are studied in detail
in the presence of anisotropic stress with the Newtonian potential generically
different from the spatial curvature perturbations. We recast this full system
of B-V equations for DM and neutrinos into a system of coupled Volterra
integral equations. These Volterra-type equations are valid both in the
radiation dominated (RD) and matter dominated (MD) eras during which the WDM
particles are ultrarelativistic and then nonrelativistic. This generalizes the
so-called Gilbert integral equation only valid for nonrelativistic particles in
the MD era. We succeed to reduce the system of four Volterra integral equations
for the density and anisotropic stress fluctuations of DM and neutrinos into a
system of only two coupled Volterra equations. The kernels and inhomogeneities
in these equations are explicitly given functions. Combining the
Boltzmann-Vlasov equations and the linearized Einstein equations constrain the
initial conditions on the distribution functions and gravitational potentials.
In the absence of neutrinos the anisotropic stress vanishes and the
Volterra-type equations reduce to a single integral equation. These Volterra
integral equations provide a useful and precise framework to compute the
primordial WDM fluctuations over a wide range of scales including small scales
up to k ~ 1/5 kpc.Comment: 26 pages, 1 figure. To appear in Phys Rev
Constraints on dark matter particles from theory, galaxy observations and N-body simulations
Mass bounds on dark matter (DM) candidates are obtained for particles
decoupling in or out of equilibrium with {\bf arbitrary} isotropic and
homogeneous distribution functions. A coarse grained Liouville invariant
primordial phase space density is introduced. Combining its
value with recent photometric and kinematic data on dwarf spheroidal satellite
galaxies in the Milky Way (dShps), the DM density today and -body
simulations, yields upper and lower bounds on the mass, primordial phase space
densities and velocity dispersion of the DM candidates. The mass of the DM
particles is bound in the few keV range. If chemical freeze out occurs before
thermal decoupling, light bosonic particles can Bose-condense. Such
Bose-Einstein {\it condensate} is studied as a dark matter candidate. Depending
on the relation between the critical()and decoupling()temperatures, a
BEC light relic could act as CDM but the decoupling scale must be {\it higher}
than the electroweak scale. The condensate tightens the upper bound on the
particle's mass. Non-equilibrium scenarios that describe particle production
and partial thermalization, sterile neutrinos produced out of equilibrium and
other DM models are analyzed in detail obtaining bounds on their mass,
primordial phase space density and velocity dispersion. Light thermal relics
with and sterile neutrinos lead to a
primordial phase space density compatible with {\bf cored} dShps and disfavor
cusped satellites. Light Bose condensed DM candidates yield phase space
densities consistent with {\bf cores} and if also with cusps.
Phase space density bounds from N-body simulations suggest a potential tension
for WIMPS with .Comment: 27 pages 8 figures. Version to appear in Phys. Rev.
Maternal Serum Meteorin Levels and the Risk of Preeclampsia
BACKGROUND: Meteorin (METRN) is a recently described neutrophic factor with angiogenic properties. This is a nested case-control study in a longitudinal cohort study that describes the serum profile of METRN during different periods of gestation in healthy and preeclamptic pregnant women. Moreover, we explore the possible application of METRN as a biomarker. METHODS AND FINDINGS: Serum METRN was measured by ELISA in a longitudinal prospective cohort study in 37 healthy pregnant women, 16 mild preeclamptic women, and 20 healthy non-pregnant women during the menstrual cycle with the aim of assessing serum METRN levels and its correlations with other metabolic parameters. Immunostaining for METRN protein was performed in placenta. A multivariate logistic regression model was proposed and a classifier model was formulated for predicting preeclampsia in early and middle pregnancy. The performance in classification was evaluated using measures such as sensitivity, specificity, and the receiver operating characteristic (ROC) curve. In healthy pregnant women, serum METRN levels were significantly elevated in early pregnancy compared to middle and late pregnancy. METRN levels are significantly lower only in early pregnancy in preeclamptic women when compared to healthy pregnant women. Decision trees that did not include METRN levels in the first trimester had a reduced sensitivity of 56% in the detection of preeclamptic women, compared to a sensitivity of 69% when METRN was included. CONCLUSIONS: The joint measurements of circulating METRN levels in the first trimester and systolic blood pressure and weight in the second trimester significantly increase the probabilities of predicting preeclampsia
CMB quadrupole suppression: II. The early fast roll stage
Within the effective field theory of inflation, an initialization of the
classical dynamics of the inflaton with approximate equipartition between the
kinetic and potential energy of the inflaton leads to a brief fast roll stage
that precedes the slow roll regime. The fast roll stage leads to an attractive
potential in the wave equations for the mode functions of curvature and tensor
perturbations. The evolution of the inflationary perturbations is equivalent to
the scattering by this potential and a useful dictionary between the scattering
data and observables is established.Implementing methods from scattering theory
we prove that this attractive potential leads to a suppression of the
quadrupole moment for CMB and B-mode angular power spectra. The scale of the
potential is determined by the Hubble parameter during slow roll. Within the
effective field theory of inflation at the grand unification (GUT) energy scale
we find that if inflation lasts a total number of efolds N_{tot} ~ 59, there is
a 10-20% suppression of the CMB quadrupole and about 2-4% suppression of the
tensor quadrupole. The suppression of higher multipoles is smaller, falling off
as 1/l^2. The suppression is much smaller for N_{tot} > 59, therefore if the
observable suppression originates in the fast roll stage, there is the upper
bound N_{tot} ~ 59.Comment: Some comments and references adde
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