19,059 research outputs found
Many-Body Dynamics and Exciton Formation Studied by Time-Resolved Photoluminescence
The dynamics of exciton and electron-hole plasma populations is studied via
time-resolved photoluminescence after nonresonant excitation. By comparing the
peak emission at the exciton resonance with the emission of the continuum, it
is possible to experimentally identify regimes where the emission originates
predominantly from exciton and/or plasma populations. The results are supported
by a microscopic theory which allows one to extract the fraction of bright
excitons as a function of time.Comment: 11 pages, 5 figure
Hyperons and massive neutron stars: vector repulsion and SU(3) symmetry
With the discovery of massive neutron stars such as PSR J1614-2230, the
question has arisen whether exotic matter such as hyperons can exist in the
neutron star core. We examine the conditions under which hyperons can exist in
massive neutron stars. We consistently investigate the vector meson-hyperon
coupling, going from SU(6) quark model to a broader SU(3) symmetry. We propose
that the maximum neutron star mass decreases linearly with the strangeness
content f_s of the neutron star core as M_max(f_s) = M_max(0) - 0.6 M_solar
(f_s/0.1), which seems to be independent of the underlying nuclear equation of
state and the vector baryon-meson coupling scheme. Thus, pulsar mass
measurements can be used to constrain the hyperon fraction in neutron stars.Comment: 13 pages, 10 figure
Excitonic Photoluminescence in Semiconductor Quantum Wells: Plasma versus Excitons
Time-resolved photoluminescence spectra after nonresonant excitation show a
distinct 1s resonance, independent of the existence of bound excitons. A
microscopic analysis identifies excitonic and electron-hole plasma
contributions. For low temperatures and low densities the excitonic emission is
extremely sensitive to even minute optically active exciton populations making
it possible to extract a phase diagram for incoherent excitonic populations.Comment: 9 pages, 4 figure
BCS BEC crossover and phase structure of relativistic system: a variational approach
We investigate here the BCS BEC crossover in relativistic systems using a
variational construct for the ground state and the minimization of the
thermodynamic potential. This is first studied in a four fermion point
interaction model and with a BCS type ansatz for the ground state with fermion
pairs. It is shown that the antiparticle degrees of freedom play an important
role in the BCS BEC crossover physics, even when the ratio of fermi momentum to
the mass of the fermion is small. We also consider the phase structure for the
case of fermion pairing with imbalanced populations. Within the ansatz,
thermodynamically stable gapless modes for both fermions and anti fermions are
seen for strong coupling in the BEC regime. We further investigate the effect
of fluctuations of the condensate field by treating it as a dynamical field and
generalize the BCS ansatz to include quanta of the condensate field also in a
boson fermion model with quartic self interaction of the condensate field. It
is seen that the critical temperature decreases with inclusion of fluctuations.Comment: 18 pages, 13 figures, one more section added, title modified, version
to appear in Phys Rev
Accelerating Universe from an Evolving Lambda in Higher Dimension
We find exact solutions in five dimensional inhomogeneous matter dominated
model with a varying cosmological constant. Adjusting arbitrary constants of
integration one can also achieve acceleration in our model. Aside from an
initial singularity our spacetime is regular everywhere including the centre of
the inhomogeneous distribution. We also study the analogous homogeneous
universe in (4+d) dimensions. Here an initially decelerating model is found to
give late acceleration in conformity with the current observational demands. We
also find that both anisotropy and number of dimensions have a role to play in
determining the time of flip, in fact the flip is delayed in multidimensional
models. Some astrophysical parameters like the age, luminosity distance etc are
also calculated and the influence of extra dimensions is briefly discussed.
Interestingly our model yields a larger age of the universe compared to many
other quintessential models.Comment: 18 pages, 9 figure
Negative forms and path space forms
We present an account of negative differential forms within a natural
algebraic framework of differential graded algebras, and explain their
relationship with forms on path spaces.Comment: 12 pp.; the Introduction has been rewritten and mention of cohomology
dropped in Proposition 3.2; material slightly reorganize
Inhomogeneities in dusty universe - a possible alternative to dark energy?
There have been of late renewed debates on the role of inhomogeneities to
explain the observed late acceleration of the universe. We have looked into the
problem analytically with the help of the well known spherically symmetric but
inhomogeneous Lemaitre-Tolman-Bondi(LTB) model generalised to higher
dimensions. It is observed that in contrast to the claim made by Kolb et al the
presence of inhomogeneities as well as extra dimensions can not reverse the
signature of the deceleration parameter if the matter field obeys the energy
conditions. The well known Raychaudhuri equation also points to the same
result. Without solving the field equations explicitly it can, however, be
shown that although the total deceleration is positive everywhere nevertheless
it does not exclude the possibility of having radial acceleration, even in the
pure dust universe, if the angular scale factor is decelerating fast enough and
vice versa. Moreover it is found that introduction of extra dimensions can not
reverse the scenario. To the contrary it actually helps the decelerating
process.Comment: 14 pages, 4 figure
Probing Supersymmetry using Event Shape variables at 8 TeV LHC
We have revisited the prospects of Supersymmetry(SUSY) searches at the LHC
with 7 TeV energy along with the prediction of the discovery potential at 8 TeV
energy assuming an integrated luminosity 5 and 20 \invfb with
mSUGRA/CMSSM as a model framework. We discuss further optimization of our
selection strategy which is based on the hadronic event shape variables.
Evaluating the standard model backgrounds and signal rates in detail we predict
the discovery reach in the plane for 7 TeV with 5\invfb
luminosity. We also present the discovery reach for 8 TeV energy with an
integrated luminosity 5\invfb and 20 \invfb. A comparison is made between
our results and the exclusion plots obtained by CMS and ATLAS. Finally,
discovery reach in the gluino and squark mass plane at the 7 TeV and 8 TeV
energy is also presented.Comment: 17 pages, 6 eps figures, 20/fb results and figures added, some
references added, version accepted and to be published in Physical Review
- …