100,942 research outputs found
Limits from Weak Gravity Conjecture on Dark Energy Models
The weak gravity conjecture has been proposed as a criterion to distinguish
the landscape from the swampland in string theory. As an application in
cosmology of this conjecture, we use it to impose theoretical constraint on
parameters of two types of dark energy models. Our analysis indicates that the
Chaplygin-gas-type models realized in quintessence field are in the swampland,
whereas the power-low decay model of the variable cosmological constant can
be viable but the parameters are tightly constrained by the conjecture.Comment: Revtex4, 8 pages, 5 figures; References, minor corrections in
content, and acknowledgement adde
The Peculiar Chemical Inventory of NGC 2419: an Extreme Outer Halo "Globular Cluster"
NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have
somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419
with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low
[Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match
the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo
Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show
that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs
Characteristics of the chiral phase transition in nonlocal quark models
The characteristics of the chiral phase transition are analyzed within the
framework of chiral quark models with nonlocal interactions in the mean field
approximation. In the chiral limit, we develop a semi-analytic framework which
allows us to explicitly determine the phase transition curve, the position of
the critical points, some relevant critical exponents, etc. For the case of
finite current quark masses, we show the behavior of various thermodynamical
and chiral response functions across the phase transition.Comment: 19 pages, 5 figures. Figures 1 and 2 modified, references added,
minor changes in the presentation and in the discussion of results. Accepted
for publication in Phys. Rev.
Weak gravity conjecture constraints on inflation
We consider the gravitational correction to the coupling of the scalar
fields. Weak gravity conjecture says that the gravitational correction to the
running of scalar coupling should be less than the contribution from scalar
fields. For instance, a new scale sets a UV cutoff
on the validity of the effective theory. Furthermore, this
conjecture implies a possible constraint on the inflation model, e.g. the
chaotic inflation model might be in the swampland.Comment: 11 pages, 3 figs; monor corrections; some clarifying remarks added
and the final version for publication in JHE
Exact Nonequilibrium Work Generating Function for a Small Classical System
We obtain the exact nonequilibrium work generating function (NEWGF), for a
small system consisting of a massive Brownian particle connected to internal
and external springs. The external work is provided to the system for a finite
time interval. The Jarzynski equality (JE), obtained in this case directly from
the NEWGF, is shown to be valid for the present model, in an exact way
regardless of the rate of external work
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Transverse momentum dependence in the perturbative calculation of pion form factor
By reanalysing transverse momentum dependence in the perturbative calculation
of pion form factor an improved expression of pion form factor which takes into
account the transverse momentum dependenc in hard scattering amplitude and
intrinsic transverse momentum dependence associated with pion wave functions is
given to leading order, which is available for momentum transfers of the order
of a few GeV as well as for . Our scheme can be extended to
evaluate the contributions to the pion form factor beyond leading order.Comment: 13 pages in LaTeX, plus 3 Postscript figure
GEOS-3 ocean current investigation using radar altimeter profiling
Both quasi-stationary and dynamic departures from the marine geoid were successfully detected using altitude measurements from the GEOS-3 radar altimeter. The quasi-stationary departures are observed either as elevation changes in single pass profiles across the Gulf Stream or at the crowding of contour lines at the western and northern areas of topographic maps generated using altimeter data spanning one month or longer. Dynamic features such as current meandering and spawned eddies can be monitored by comparing monthly mean maps. Comparison of altimeter inferred eddies with IR detected thermal rings indicates agreement of the two techniques. Estimates of current velocity are made using derived slope estimates in conjunction with the geostrophic equation
Studies related to ocean dynamics. Task 3.2: Aircraft Field Test Program to investigate the ability of remote sensing methods to measure current/wind-wave interactions
The feasibility of remote sensing of current flows in the ocean and the remote sensing of ocean currents by backscattering cross section techniques was studied. It was established that for capillary waves, small scale currents could be accurately measured through observation of wave kinematics. Drastic modifications of waves by changing currents were noted. The development of new methods for the measurement of capillary waves are discussed. Improvement methods to resolve data processing problems are suggested
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