120 research outputs found
Estimating the amount of vorticity generated by cosmological perturbations in the early universe
We estimate the amount of vorticity generated at second order in cosmological
perturbation theory from the coupling between first order energy density and
non-adiabatic pressure, or entropy, perturbations. Assuming power law input
spectra for the source terms, and working in a radiation background, we
calculate the wave number dependence of the vorticity power spectrum and its
amplitude. We show that the vorticity generated by this mechanism is
non-negligible on small scales, and hence should be taken into consideration in
current and future CMB experiments.Comment: 9 pages, revtex4, 1 figure; v2: typos and minor error corrected,
result unchange
Effective Hamiltonian study of excitations in a boson- fermion mixture with attraction between components
An effective Hamiltonian for the Bose subsystem in the mixture of ultracold
atomic clouds of bosons and fermions with mutual attractive interaction is used
for investigating collective excitation spectrum. The ground state and mode
frequencies of the Rb and K mixture are analyzed quantitatively
at zero temperature. We find analytically solutions of the hydrodynamics
equations in the Thomas- Fermi approximation. We discuss the relation between
the onset of collapse and collective modes softening and the dependence of
collective oscillations on scattering length and number of boson atoms.Comment: 9 pages, 5 figure
Comments on gauge-invariance in cosmology
We revisit the gauge issue in cosmological perturbation theory, and highlight
its relation to the notion of covariance in general relativity. We also discuss
the similarities and differences of the covariant approach in perturbation
theory to the Bardeen or metric approach in a non-technical fashion.Comment: 7 pages, 1 figure, revtex4; v3: minor changes, typos corrected,
discussion extended; v4: typos corrected, corresponding to published versio
Quantum quench spectroscopy of a Luttinger liquid: Ultrarelativistic density wave dynamics due to fractionalization in an XXZ chain
We compute the dynamics of localized excitations produced by a quantum quench
in the spin 1/2 XXZ chain. Using numerics combining the density matrix
renormalization group and exact time evolution, as well as analytical
arguments, we show that fractionalization due to interactions in the pre-quench
state gives rise to "ultrarelativistic" density waves that travel at the
maximum band velocity. The system is initially prepared in the ground state of
the chain within the gapless XY phase, which admits a Luttinger liquid (LL)
description at low energies and long wavelengths. The Hamiltonian is then
suddenly quenched to a band insulator, after which the chain evolves unitarily.
Through the gapped dispersion of the insulator spectrum, the post-quench
dynamics serve as a "velocity microscope," revealing initial state particle
correlations via space time density propagation. We show that the
ultrarelativistic wave production is tied to the particular way in which
fractionalization evades Pauli-blocking in the zero-temperature initial LL
state.Comment: 32 pages, 27 figures; v2: references update
Inferring the time-dependent complex Ginzburg-Landau equation from modulus data
We present a formalism for inferring the equation of evolution of a complex
wave field that is known to obey an otherwise unspecified (2+1)-dimensional
time-dependent complex Ginzburg-Landau equation, given field moduli over three
closely-spaced planes. The phase of the complex wave field is retrieved via a
non-interferometric method, and all terms in the equation of evolution are
determined using only the magnitude of the complex wave field. The formalism is
tested using simulated data for a generalized nonlinear system with a
single-component complex wave field. The method can be generalized to
multi-component complex fields.Comment: 9 pages, 9 figure
Electroweak baryogenesis induced by a scalar field
A cosmological pseudoscalar field coupled to hypercharge topological number
density can exponentially amplify hyperelectric and hypermagnetic fields while
coherently rolling or oscillating, leading to the formation of a time-dependent
condensate of topological number density. The topological condensate can be
converted, under certain conditions, into baryons in sufficient quantity to
explain the observed baryon asymmetry in the universe. The amplified
hypermagnetic field can perhaps sufficiently strengthen the electroweak phase
transition, and by doing so, save any pre-existing baryon number asymmetry from
extinction.Comment: 8 pages, 4 figure
Fourier-Space Crystallography as Group Cohomology
We reformulate Fourier-space crystallography in the language of cohomology of
groups. Once the problem is understood as a classification of linear functions
on the lattice, restricted by a particular group relation, and identified by
gauge transformation, the cohomological description becomes natural. We review
Fourier-space crystallography and group cohomology, quote the fact that
cohomology is dual to homology, and exhibit several results, previously
established for special cases or by intricate calculation, that fall
immediately out of the formalism. In particular, we prove that {\it two phase
functions are gauge equivalent if and only if they agree on all their
gauge-invariant integral linear combinations} and show how to find all these
linear combinations systematically.Comment: plain tex, 14 pages (replaced 5/8/01 to include archive preprint
number for reference 22
Renormalization group study of interacting electrons
The renormalization-group (RG) approach proposed earlier by Shankar for
interacting spinless fermions at is extended to the case of non-zero
temperature and spin. We study a model with -invariant short-range
effective interaction and rotationally invariant Fermi surface in two and three
dimensions. We show that the Landau interaction function of the Fermi liquid,
constructed from the bare parameters of the low-energy effective action, is RG
invariant. On the other hand, the physical forward scattering vertex is found
as a stable fixed point of the RG flow. We demonstrate that in and 3, the
RG approach to this model is equivalent to Landau's mean-field treatment of the
Fermi liquid. We discuss subtleties associated with the symmetry properties of
the scattering amplitude, the Landau function and the low-energy effective
action. Applying the RG to response functions, we find the compressibility and
the spin susceptibility as fixed points.Comment: 11 pages, RevTeX 3.0, 2 PostScript figure
Hot String Soup
Above the Hagedorn energy density closed fundamental strings form a long
string phase. The dynamics of weakly interacting long strings is described by a
simple Boltzmann equation which can be solved explicitly for equilibrium
distributions. The average total number of long strings grows logarithmically
with total energy in the microcanonical ensemble. This is consistent with
calculations of the free single string density of states provided the
thermodynamic limit is carefully defined. If the theory contains open strings
the long string phase is suppressed.Comment: 13 pages, no figures, uses LaTex, some errors in equations have been
corrected, NSF-ITP-94-83, UCSBTH-94-3
Recommended from our members
Experimental Traumatic Brain Injury Induces Chronic Glutamatergic Dysfunction in Amygdala Circuitry Known to Regulate Anxiety-Like Behavior
Up to 50% of traumatic brain injury (TBI) survivors demonstrate persisting and late-onset anxiety disorders indicative of limbic system dysregulation, yet the pathophysiology underlying the symptoms is unclear. We hypothesize that the development of TBI-induced anxiety-like behavior in an experimental model of TBI is mediated by changes in glutamate neurotransmission within the amygdala. Adult, male Sprague-Dawley rats underwent midline fluid percussion injury or sham surgery. Anxiety-like behavior was assessed at 7 and 28 days post-injury (DPI) followed by assessment of real-time glutamate neurotransmission in the basolateral amygdala (BLA) and central nucleus of the amygdala (CeA) using glutamate-selective microelectrode arrays. The expression of anxiety-like behavior at 28 DPI coincided with decreased evoked glutamate release and slower glutamate clearance in the CeA, not BLA. Numerous factors contribute to the changes in glutamate neurotransmission over time. In two additional animal cohorts, protein levels of glutamatergic transporters (Glt-1 and GLAST) and presynaptic modulators of glutamate release (mGluR2, TrkB, BDNF, and glucocorticoid receptors) were quantified using automated capillary western techniques at 28 DPI. Astrocytosis and microglial activation have been shown to drive maladaptive glutamate signaling and were histologically assessed over 28 DPI. Alterations in glutamate neurotransmission could not be explained by changes in protein levels for glutamate transporters, mGluR2 receptors, astrocytosis, and microglial activation. Presynaptic modulators, BDNF and TrkB, were significantly decreased at 28 DPI in the amygdala. Dysfunction in presynaptic regulation of glutamate neurotransmission may contribute to anxiety-related behavior and serve as a therapeutic target to improve circuit function.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
- …