368 research outputs found
A Hybrid Model for QCD Deconfining Phase Boundary
Intensive search for a proper and realistic equations of state (EOS) is still
continued for studying the phase diagram existing between quark gluon plasma
(QGP) and hadron gas (HG) phases. Lattice calculations provide such EOS for the
strongly interacting matter at finite temperature () and vanishing baryon
chemical potential (). These calculations are of limited use at finite
due to the appearance of notorious sign problem. In the recent past,
we had constructed a hybrid model description for the QGP as well as HG phases
where we make use of a new excluded-volume model for HG and a
thermodynamically-consistent quasiparticle model for the QGP phase and used
them further to get QCD phase boundary and a critical point. Since then many
lattice calculations have appeared showing various thermal and transport
properties of QCD matter at finite and . We test our hybrid
model by reproducing the entire data for strongly interacting matter and
predict our results at finite so that they can be tested in future.
Finally we demonstrate the utility of the model in fixing the precise location,
the order of the phase transition and the nature of CP existing on the QCD
phase diagram. We thus emphasize the suitability of the hybrid model as
formulated here in providing a realistic EOS for the strongly interacting
matter.Comment: 22 pages, 10 figures. corrected version published in Physical Review
D. arXiv admin note: substantial text overlap with arXiv:1201.044
Bose-Einstein Condensates in Optical Quasicrystal Lattices
We analyze the physics of Bose-Einstein condensates confined in 2D
quasi-periodic optical lattices, which offer an intermediate situation between
ordered and disordered systems. First, we analyze the time-of-flight
interference pattern that reveals quasi-periodic long-range order. Second, we
demonstrate localization effects associated with quasi-disorder as well as
quasiperiodic Bloch oscillations associated with the extended nature of the
wavefunction of a Bose-Einstein condensate in an optical quasicrystal. In
addition, we discuss in detail the crossover between diffusive and localized
regimes when the quasi-periodic potential is switched on, as well as the
effects of interactions
A systematic correlation between two-dimensional flow topology and the abstract statistics of turbulence
Velocity differences in the direct enstrophy cascade of two-dimensional
turbulence are correlated with the underlying flow topology. The statistics of
the transverse and longitudinal velocity differences are found to be governed
by different structures. The wings of the transverse distribution are dominated
by strong vortex centers, whereas, the tails of the longitudinal differences
are dominated by saddles. Viewed in the framework of earlier theoretical work
this result suggests that the transfer of enstrophy to smaller scales is
accomplished in regions of the flow dominated by saddles.Comment: 4 pages, 4 figure
A comparison of spectral element and finite difference methods using statically refined nonconforming grids for the MHD island coalescence instability problem
A recently developed spectral-element adaptive refinement incompressible
magnetohydrodynamic (MHD) code [Rosenberg, Fournier, Fischer, Pouquet, J. Comp.
Phys. 215, 59-80 (2006)] is applied to simulate the problem of MHD island
coalescence instability (MICI) in two dimensions. MICI is a fundamental MHD
process that can produce sharp current layers and subsequent reconnection and
heating in a high-Lundquist number plasma such as the solar corona [Ng and
Bhattacharjee, Phys. Plasmas, 5, 4028 (1998)]. Due to the formation of thin
current layers, it is highly desirable to use adaptively or statically refined
grids to resolve them, and to maintain accuracy at the same time. The output of
the spectral-element static adaptive refinement simulations are compared with
simulations using a finite difference method on the same refinement grids, and
both methods are compared to pseudo-spectral simulations with uniform grids as
baselines. It is shown that with the statically refined grids roughly scaling
linearly with effective resolution, spectral element runs can maintain accuracy
significantly higher than that of the finite difference runs, in some cases
achieving close to full spectral accuracy.Comment: 19 pages, 17 figures, submitted to Astrophys. J. Supp
Constraints on the Universal Varying Yukawa Couplings: from SM-like to Fermiophobic
Varying the Standard Model (SM) fermion Yukawa couplings universally by a
generic positive scale factor (), we study the phenomenological fit to
the current available experimental results for the Higgs boson search at hadron
colliders. We point out that the Higgs production cross section and its decay
branching ratio to can be varied oppositely by to make
their product almost invariant. Thus, our scenario and the SM Higgs are
indistinguishable in the inclusive channel. The current
measurements on direct Yukawa coupling strength in the
channel are not precise enough to fix the scale factor . The most
promising is the vector-boson-fusion channel in which the CMS has already
observed possible suppression effect on the Yukawa couplings. Further more, the
global fit of the experimental data can get the optimal value by
introducing a suppression factor on the SM Yukawa couplings.Comment: 16 pages, 12 figures, 5 tables, update analysis is supplemente
Exploring \pp scattering in the \1N picture
In the large approximation to , the leading \pp scattering
amplitude is expressed as the sum of an infinite number of tree diagrams. We
investigate the possibility that an adequate approximation at energies up to
somewhat more than one can be made by keeping diagrams which involve the
exchange of resonances in this energy range in addition to the simplest chiral
contact terms. In this approach crossing symmetry is automatic but individual
terms tend to drastically violate partial wave unitarity. We first note that
the introduction of the meson in a chirally invariant manner
substantially delays the onset of drastic unitarity violation which would be
present for the {\it current algebra} term alone. This suggests a possibility
of local (in energy) cancellation which we then explore in a phenomenological
way. We include exchanges of leading resonances up to the region.
However, unitarity requires more structure which we model by a four derivative
contact term or by a low lying scalar resonance which is presumably subleading
in the \1N expansion, but may nevertheless be important. The latter two
flavor model gives a reasonable description of the phase shift up
until around , before the effects associated which the
threshold come into play.Comment: 27 LaTex pages + 13 figures (also available in hard-copy
Dynamical Evolution of the Scalar Condensate in Heavy Ion Collisions
We derive the effective coarse-grained field equation for the scalar
condensate of the linear sigma model in a simple and straightforward manner
using linear response theory. The dissipative coefficient is calculated at tree
level on the basis of the physical processes of sigma-meson decay and of
thermal sigma-mesons and pions knocking sigma-mesons out of the condensate. The
field equation is solved for hot matter undergoing either one or three
dimensional expansion and cooling in the aftermath of a high energy nuclear
collision. The results show that the time constant for returning the scalar
condensate to thermal equilibrium is of order 2 fm/c.Comment: 19 pages, 3 figures are embedded at the end. The effect of the time
dependence of the condensate v is included in this revised version. Numerical
work is redone accordingl
Graduate Quantum Mechanics Reform
We address four main areas in which graduate quantum mechanics education can
be improved: course content, textbook, teaching methods, and assessment tools.
We report on a three year longitudinal study at the Colorado School of Mines
using innovations in all these areas. In particular, we have modified the
content of the course to reflect progress in the field in the last 50 years,
used textbooks that include such content, incorporated a variety of teaching
techniques based on physics education research, and used a variety of
assessment tools to study the effectiveness of these reforms. We present a new
assessment tool, the Graduate Quantum Mechanics Conceptual Survey, and further
testing of a previously developed assessment tool, the Quantum Mechanics
Conceptual Survey. We find that graduate students respond well to
research-based techniques that have been tested mainly in introductory courses,
and that they learn much of the new content introduced in each version of the
course. We also find that students' ability to answer conceptual questions
about graduate quantum mechanics is highly correlated with their ability to
solve calculational problems on the same topics. In contrast, we find that
students' understanding of basic undergraduate quantum mechanics concepts at
the modern physics level is not improved by instruction at the graduate level.Comment: accepted to American Journal of Physic
On the dual cascade in two-dimensional turbulence
We study the dual cascade scenario for two-dimensional turbulence driven by a
spectrally localized forcing applied over a finite wavenumber range
[k_\min,k_\max] (with k_\min > 0) such that the respective energy and
enstrophy injection rates and satisfy
k_\min^2\epsilon\le\eta\le k_\max^2\epsilon. The classical
Kraichnan--Leith--Batchelor paradigm, based on the simultaneous conservation of
energy and enstrophy and the scale-selectivity of the molecular viscosity,
requires that the domain be unbounded in both directions. For two-dimensional
turbulence either in a doubly periodic domain or in an unbounded channel with a
periodic boundary condition in the across-channel direction, a direct enstrophy
cascade is not possible. In the usual case where the forcing wavenumber is no
greater than the geometric mean of the integral and dissipation wavenumbers,
constant spectral slopes must satisfy and , where
() is the asymptotic slope of the range of wavenumbers lower
(higher) than the forcing wavenumber. The influence of a large-scale
dissipation on the realizability of a dual cascade is analyzed. We discuss the
consequences for numerical simulations attempting to mimic the classical
unbounded picture in a bounded domain.Comment: 22 pages, to appear in Physica
Dynamics of a small neutrally buoyant sphere in a fluid and targeting in Hamiltonian systems
We show that, even in the most favorable case, the motion of a small
spherical tracer suspended in a fluid of the same density may differ from the
corresponding motion of an ideal passive particle. We demonstrate furthermore
how its dynamics may be applied to target trajectories in Hamiltonian systems.Comment: See home page http://lec.ugr.es/~julya
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