5,945 research outputs found
Supersymmetry and Goldstino-like Mode in Bose-Fermi Mixtures
Supersymmetry is assumed to be a basic symmetry of the world in many high
energy theories, but none of the super partners of any known elementary
particle has been observed yet. We argue that supersymmetry can also be
realized and studied in ultracold atomic systems with a mixture of bosons and
fermions, with properly tuned interactions and single particle dispersion. We
further show that in such non-releativistic systems supersymmetry is either
spontaneously broken, or explicitly broken by a chemical potential difference
between the bosons and fermions. In both cases the system supports a sharp
fermionic collective mode or the so-called Goldstino, due to supersymmetry. We
also discuss possible ways to detect the Goldstino mode experimentally.Comment: 4 pages. V4: published versio
Exact phase diagrams for an Ising model on a two-layer Bethe lattice
Using an iteration technique, we obtain exact expressions for the free energy
and the magnetization of an Ising model on a two - layer Bethe lattice with
intralayer coupling constants J1 and J2 for the first and the second layer,
respectively, and interlayer coupling constant J3 between the two layers; the
Ising spins also couple with external magnetic fields, which are different in
the two layers. We obtain exact phase diagrams for the system.Comment: 24 pages, 2 figures. To be published in Phys. Rev. E 59, Issue 6,
199
The intermediate-mass star-forming region Lynds 1340. An optical view
We have performed an optical spectroscopic and photometric search for young
stellar objects associated with the molecular cloud Lynds 1340, and examined
the structure of the cloud by constructing an extinction map, based on SDSS
data. The new extinction map suggests a shallow, strongly fragmented cloud,
having a mass of some 3700~Msun. Longslit spectroscopic observations of the
brightest stars over the area of L1340 revealed that the most massive star
associated with L1340 is a B4 type, about 5 solar mass star. The new
spectroscopic and photometric data of the intermediate mass members led to a
revised distance of 825 (+110 /-80) pc, and revealed seven members of the young
stellar population with M > 2 solar masses. Our search for H alpha emission
line stars, conducted with the Wide Field Grism Spectrograph 2 on the 2.2-meter
telescope of the University of Hawaii and covering a 30 arcmin x 40 arcmin
area, resulted in the detection of 75 candidate low-mass pre-main sequence
stars, 58 of which are new. We constructed spectral energy distributions of our
target stars, based on SDSS, 2MASS, Spitzer, and WISE photometric data, derived
their spectral types, extinctions, and luminosities from BVRIJ fluxes,
estimated masses by means of pre-main sequence evolutionary models, and
examined the disk properties utilizing the 2-24 micron interval of the spectral
energy distribution. We measured the equivalent width of the H alpha lines and
derived accretion rates. The optically selected sample of pre-main sequence
stars has a median effective temperature of 3970 K, stellar mass 0.7 Msun, and
accretion rate of 7.6 10^{-9} Msun/yr.Comment: 47 pages, 15 figures, 10 tables; accepted for publication in ApJ,
typos correcte
The Asymmetric Avalanche Process
An asymmetric stochastic process describing the avalanche dynamics on a ring
is proposed. A general kinetic equation which incorporates the exclusion and
avalanche processes is considered. The Bethe ansatz method is used to calculate
the generating function for the total distance covered by all particles. It
gives the average velocity of particles which exhibits a phase transition from
an intermittent to continuous flow. We calculated also higher cumulants and the
large deviation function for the particle flow. The latter has the universal
form obtained earlier for the asymmetric exclusion process and conjectured to
be common for all models of the Kardar-Parisi-Zhang universality class .Comment: 33 pages, 3 figures, revised versio
Break-up of shells under explosion and impact
A theoretical and experimental study of the fragmentation of closed thin
shells made of a disordered brittle material is presented. Experiments were
performed on brown and white hen egg-shells under two different loading
conditions: fragmentation due to an impact with a hard wall and explosion by a
combustion mixture giving rise to power law fragment size distributions. For
the theoretical investigations a three-dimensional discrete element model of
shells is constructed. Molecular dynamics simulations of the two loading cases
resulted in power law fragment mass distributions in satisfactory agreement
with experiments. Based on large scale simulations we give evidence that power
law distributions arise due to an underlying phase transition which proved to
be abrupt and continuous for explosion and impact, respectively. Our results
demonstrate that the fragmentation of closed shells defines a universality
class different from that of two- and three-dimensional bulk systems.Comment: 11 pages, 14 figures in eps forma
- …