898 research outputs found
Thermal field theory of bosonic gases with finite-range effective interaction
We study a dilute and ultracold Bose gas of interacting atoms by using an
effective field theory which takes account finite-range effects of the
inter-atomic potential. Within the formalism of functional integration from the
grand canonical partition function we derive beyond-mean-field analytical
results which depend on both scattering length and effective range of the
interaction. In particular, we calculate the equation of state of the bosonic
system as a function of these interaction parameters both at zero and finite
temperature including one-loop Gaussian fluctuation. In the case of zero-range
effective interaction we explicitly show that, due to quantum fluctuations, the
bosonic system is thermodynamically stable only for very small values of the
gas parameter. We find that a positive effective range above a critical
threshold is necessary to remove the thermodynamical instability of the uniform
configuration. Remarkably, also for relatively large values of the gas
parameter, our finite-range results are in quite good agreement with recent
zero-temperature Monte Carlo calculations obtained with hard-sphere bosons.Comment: 6 pages, 2 figures, added some equation
Finite-Range Corrections to the Thermodynamics of the One-Dimensional Bose Gas
The Lieb-Liniger equation of state accurately describes the zero-temperature
universal properties of a dilute one-dimensional Bose gas in terms of the
s-wave scattering length. For weakly-interacting bosons we derive non-universal
corrections to this equation of state taking into account finite-range effects
of the inter-atomic potential. Within the finite-temperature formalism of
functional integration we find a beyond-mean-field equation of state which
depends on scattering length and effective range of the interaction potential.
Our analytical results, which are obtained performing dimensional
regularization of divergent zero-point quantum fluctuations, show that for the
one-dimensional Bose gas thermodynamic quantities like pressure and sound
velocity are modified by changing the ratio between the effective range and the
scattering length.Comment: 6 pages, 2 figures, accepted for publication in Physical Review
Condensation and superfluidity of dilute Bose gases with finite-range interaction
We investigate an ultracold and dilute Bose gas by taking into account a
finite-range two-body interaction. The coupling constants of the resulting
Lagrangian density are related to measurable scattering parameters by following
the effective-field-theory approach. A perturbative scheme is then developed up
to the Gaussian level, where both quantum and thermal fluctuations are
crucially affected by finite-range corrections. In particular, the relation
between spontaneous symmetry breaking and the onset of superfluidity is
emphasized by recovering the renowned Landau's equation for the superfluid
density in terms of the condensate one.Comment: 18 pages, 4 figures, invited contribution to New Journal of Physics
Focus Issue on Quantum Transport in Ultracold Atom
Collisionless Dynamics in Two-Dimensional Bosonic Gases
We study the dynamics of dilute and ultracold bosonic gases in a quasi
two-dimensional (2D) configuration and in the collisionless regime. We adopt
the 2D Landau-Vlasov equation to describe a three-dimensional gas under very
strong harmonic confinement along one direction. We use this effective equation
to investigate the speed of sound in quasi 2D bosonic gases, i.e. the sound
propagation around a Bose-Einstein distribution in collisionless 2D gases. We
derive coupled algebraic equations for the real and imaginary parts of the
sound velocity, which are then solved taking also into account the equation of
state of the 2D bosonic system. Above the Berezinskii-Kosterlitz-Thouless
critical temperature we find that there is rapid growth of the imaginary
component of the sound velocity which implies a strong Landau damping. Quite
remarkably, our theoretical results are in good agreement with very recent
experimental data obtained with a uniform 2D Bose gas of Rb atoms.Comment: 5 pages, 2 figures, improved introduction and conclusions, accepted
for publication in Physical Review
Nonequilibrium Kinetics of One-Dimensional Bose Gases
We study cold dilute gases made of bosonic atoms, showing that in the
mean-field one-dimensional regime they support stable out-of-equilibrium
states. Starting from the 3D Boltzmann-Vlasov equation with contact
interaction, we derive an effective 1D Landau-Vlasov equation under the
condition of a strong transverse harmonic confinement. We investigate the
existence of out-of-equilibrium states, obtaining stability criteria similar to
those of classical plasmas.Comment: 16 pages, 6 figures, accepted for publication in Journal of
Statistical Mechanics: Theory and Experimen
The Generation and Dissipation of Interstellar Turbulence - Results from Large Scale High Resolution Simulations
We study, by means of adaptive mesh refinement hydro- and
magnetohydrodynamical simulations that cover a wide range of scales (from kpc
to sub-parsec), the dimension of the most dissipative structures and the
injection scale of the turbulent interstellar gas, which we find to be about 75
pc, in agreement with observations. This is however smaller than the average
size of superbubbles, but consistent with significant density and pressure
changes in the ISM, which leads to the break-up of bubbles locally and hence to
injection of turbulence. The scalings of the structure functions are consistent
with log-Poisson statistics of supersonic turbulence where energy is dissipated
mainly through shocks. Our simulations are different from previous ones by
other authors as (i) we do not assume an isothermal gas, but have temperature
variations of several orders of magnitude and (ii) we have no artificial
forcing of the fluid with some ad hoc Fourier spectrum, but drive turbulence by
stellar explosions at the Galactic rate, self-regulated by density and
temperature thresholds imposed on the ISM gas.Comment: Five pages and three figures. Accepted for publication in
Astrophysical Journal (Letters
Detection of a light echo from SN1998bu
About 500d after explosion the light curve of the Type Ia SN1998bu suddenly
flattened and at the same time the spectrum changed from the typical nebular
emission to a blue continuum with broad absorption and emission features
reminiscent of the SN spectrum at early phases. We show that in analogy to
SN1991Tbu (Schmidt et al. 1994), this can be explained by the emergence of a
light echo from a foreground dust cloud. Based on a simple model we argue that
the amount of dust required can consistently explain the extinction which has
been estimated by completely independent methods. Because of the similar echo
luminosity but much higher optical depth of the dust in SN1998bu compared with
SN1991T, we expect that the echo ring size of SN1998bu grows faster than in
SN1991T. HST observations have indeed confirmed this prediction.Comment: 5 pages (including 3 figures) - Accepted for pubblication in ApJ
Letter
The Rates of Hypernovae and Gamma-Ray Bursts: Implications for their Progenitors
A critical comparison of estimates for the rates of hypernovae (HNe) and
gamma-ray bursts (GRBs) is presented. Within the substantial uncertainties, the
estimates are shown to be quite comparable and give a Galactic rate of
-- yr for both events. These rates are several
orders of magnitude lower than the rate of core-collapse supernovae, suggesting
that the evolution leading to a HN/GRB requires special circumstances, very
likely due to binary interactions. Various possible binary channels are
discussed, and it is shown that these are generally compatible with the
inferred rates.Comment: Accepted by Astrophysical Journal Letters. 12 page
Nebular Spectra of SN 1998bw Revisited: Detailed Study by One and Two Dimensional Models
Refined one- and two-dimensional models for the nebular spectra of the
hyper-energetic Type Ic supernova (SN) 1998bw, associated with the gamma-ray
burst GRB980425, from 125 to 376 days after B-band maximum are presented. One
dimensional, spherically symmetric spectrum synthesis calculations show that
reproducing features in the observed spectra, i.e., the sharply peaked [OI]
6300\AA doublet and MgI] 4570\AA emission, and the broad [FeII] blend around
5200\AA, requires the existence of a high-density O-rich core expanding at low
velocities (\lsim 8,000 km s) and of Fe-rich material moving faster
than the O-rich material. Synthetic spectra at late phases from aspherical
(bipolar) explosion models are also computed with a two-dimensional spectrum
synthesis code. The above features are naturally explained by the aspherical
model if the explosion is viewed from a direction close to the axis of symmetry
(), since the aspherical model yields a high-density O-rich
region confined along the equatorial axis. By examining a large parameter space
(in energy and mass), our best model gives following physical quantities: the
kinetic energy ergs \gsim 8 - 12 and the
main-sequence mass of the progenitor star M_{\rm ms} \gsim 30 - 35 \Msun. The
temporal spectral evolution of SN 1998bw also indicates mixing among Fe-, O-,
and C-rich regions, and highly clumpy structure.Comment: 38 pages, 22 figures. ApJ, 640 (01 April 2006 issue), in pres
Why Are Radio-Galaxies Prolific Producers of Type Ia Supernovae?
An analysis of SNIa events in early type galaxies from the Cappellaro et al
(1999) database provides conclusive evidence that the rate of type Ia
Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate
measured in radio-quiet galaxies, i.e. SNIa-rate SNu as compared to SNIa-rate SNu. The actual value of the
enhancement is likely to be in the range (P). This
finding puts on robust empirical grounds the results obtained by Della Valle &
Panagia (2003) on the basis of a smaller sample of SNe. We analyse the possible
causes of this result and conclude that the enhancement of SNIa explosion rate
in radio-loud galaxies has the same origin as their being strong radio sources,
but there is no causality link between the two phenomena. We argue that
repeated episodes of interaction and/or mergers of early type galaxies with
dwarf companions, on times-scale of about 1 Gyr, are responsible for inducing
both strong radio activity observed in 14% of early type galaxies and to
supply an adequate number of SNIa progenitors to the stellar population of
ellipticals.Comment: 26 pages+6 figures, ApJ, in pres
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