670 research outputs found
Covariant Effective Action and One-Loop Renormalization of 2D Dilaton Gravity with Fermionic Matter
Two dimensional dilaton gravity interacting with a four-fermion model and
scalars is investigated, all the coefficients of the Lagrangian being arbitrary
functions of the dilaton field. The one-loop covariant effective action for 2D
dilaton gravity with Majorana spinors (including the four-fermion interaction)
is obtained, and the technical problems which appear in an attempt at
generalizing such calculations to the case of the most general four-fermion
model described by Dirac fermions are discussed. A solution to these problems
is found, based on its reduction to the Majorana spinor case.
The general covariant effective action for 2D dilaton gravity with the
four-fermion model described by Dirac spinors is given. The one-loop
renormalization of dilaton gravity with Majorana spinors is carried out and the
specific conditions for multiplicative renormalizability are found. A
comparison with the same theory but with a classical gravitational field is
done.Comment: LaTeX, 25 pages, july 2
Interacting Ricci Dark Energy and its Statefinder Description
In this paper we have considered an interacting Ricci dark energy in flat FRW
universe. We have reconstructed the Hubble's parameter under this interaction.
Also, we have investigated the statefinder diagnostics. It has been revealed
that the equation of state parameter behaves like quintessence in this
interaction and from the statefinder diagnostics it has been concluded that the
interacting Ricci dark energy interpolates between dust and CDM stages
of the universe.Comment: 9 pages, 3 figure
A solution of the coincidence problem based on the recent galactic core black hole mass density increase
A mechanism capable to provide a natural solution to two major cosmological
problems, i.e. the cosmic acceleration and the coincidence problem, is
proposed. A specific brane-bulk energy exchange mechanism produces a total dark
pressure, arising when adding all normal to the brane negative pressures in the
interior of galactic core black holes. This astrophysically produced negative
dark pressure explains cosmic acceleration and why the dark energy today is of
the same order to the matter density for a wide range of the involved
parameters. An exciting result of the analysis is that the recent rise of the
galactic core black hole mass density causes the recent passage from cosmic
deceleration to acceleration. Finally, it is worth mentioning that this work
corrects a wide spread fallacy among brane cosmologists, i.e. that escaping
gravitons result to positive dark pressure.Comment: 14 pages, 3 figure
Partial Deconfinement in Color Superconductivity
We analyze the fate of the unbroken SU(2) color gauge interactions for 2
light flavors color superconductivity at non zero temperature. Using a simple
model we compute the deconfining/confining critical temperature and show that
is smaller than the critical temperature for the onset of the superconductive
state itself. The breaking of Lorentz invariance, induced already at zero
temperature by the quark chemical potential, is shown to heavily affect the
value of the critical temperature and all of the relevant features related to
the deconfining transition. Modifying the Polyakov loop model to describe the
SU(2) immersed in the diquark medium we argue that the deconfinement transition
is second order. Having constructed part of the equation of state for the 2
color superconducting phase at low temperatures our results are relevant for
the physics of compact objects featuring a two flavor color superconductive
state.Comment: 9 pp, 4 eps-figs, version to appear in PR
Scalar-Tensor Theory of Gravity and Generalized Second Law of Thermodynamics on the Event Horizon
In blackhole physics, the second law of thermodynamics is generally valid
whether the blackhole is a static or a non-static one. Considering the universe
as a thermodynamical system the second law of blackhole dynamics extends to the
non-negativity of the sum of the entropy of the matter and the horizon, known
as generalized second law of thermodynamics(GSLT). Here, we have assumed the
universe to be bounded by the event-horizon or filled with perfect fluid and
holographic dark energy in two cases. Thus considering entropy to be an
arbitrary function of the area of the event-horizon, we have tried to find the
conditions and the restrictions over the scalar field and equation of state for
the validity of the GSLT and both in quintessence-era and in phantom-era in
scalar tensor theory.Comment: 8 page
Validity of the Generalized Second Law of Thermodynamics of the Universe Bounded by the Event Horizon in Holographic Dark Energy Model
In this letter, we investigate the validity of the generalized second law of
thermodynamics of the universe bounded by the event horizon in the holographic
dark energy model. The universe is chosen to be homogeneous and isotropic and
the validity of the first law has been assumed here. The matter in the universe
is taken in the form of non-interacting two fluid system- one component is the
holographic dark energy model and the other component is in the form of dust.Comment: 8 page
A genomic portrait of the emergence, evolution, and global spread of a methicillin-resistant staphylococcus aureus pandemic
The widespread use of antibiotics in association with high-density clinical care has driven the emergence of drug-resistant bacteria that are adapted to thrive in hospitalized patients. Of particular concern are globally disseminated methicillin-resistant Staphylococcus aureus (MRSA) clones that cause outbreaks and epidemics associated with health care. The most rapidly spreading and tenacious health-care-associated clone in Europe currently is EMRSA-15, which was first detected in the UK in the early 1990s and subsequently spread throughout Europe and beyond. Using phylogenomic methods to analyze the genome sequences for 193 S. aureus isolates, we were able to show that the current pandemic population of EMRSA-15 descends from a health-care-associated MRSA epidemic that spread throughout England in the 1980s, which had itself previously emerged from a primarily community-associated methicillin-sensitive population. The emergence of fluoroquinolone resistance in this EMRSA-15 subclone in the English Midlands during the mid-1980s appears to have played a key role in triggering pandemic spread, and occurred shortly after the first clinical trials of this drug. Genome-based coalescence analysis estimated that the population of this subclone over the last 20 yr has grown four times faster than its progenitor. Using comparative genomic analysis we identified the molecular genetic basis of 99.8% of the antimicrobial resistance phenotypes of the isolates, highlighting the potential of pathogen genome sequencing as a diagnostic tool. We document the genetic changes associated with adaptation to the hospital environment and with increasing drug resistance over time, and how MRSA evolution likely has been influenced by country-specific drug use regimens
Polyakov Loops versus Hadronic States
The order parameter for the pure Yang-Mills phase transition is the Polyakov
loop which encodes the symmetries of the Z_N center of the SU(N) gauge group.
On the other side the physical degrees of freedom of any asymptotically free
gauge theory are hadronic states. Using the Yang-Mills trace anomaly and the
exact Z_N symmetry we construct a model able to communicate to the hadrons the
information carried by the order parameter.Comment: RevTex4 2-col., 6 pages, 2 figures. Typos fixed and added a paragraph
in the conclusion
Effective Lagrangians for Orientifold Theories
We construct effective Lagrangians of the Veneziano-Yankielowicz (VY) type
for two non-supersymmetric theories which are orientifold daughters of
supersymmetric gluodynamics (containing one Dirac fermion in the two-index
antisymmetric or symmetric representation of the gauge group). Since the parent
and daughter theories are planar equivalent, at N\to\infty the effective
Lagrangians in the orientifold theories basically coincide with the bosonic
part of the VY Lagrangian.
We depart from the supersymmetric limit in two ways. First, we consider
finite (albeit large) values of N. Then 1/N effects break supersymmetry. We
suggest seemingly the simplest modification of the VY Lagrangian which
incorporates these 1/N effects, leading to a non-vanishing vacuum energy
density. We analyze the spectrum of the finite-N non-supersymmetric daughters.
For N=3 the two-index antisymmetric representation (one flavor) is equivalent
to one-flavor QCD. We show that in this case the scalar quark-antiquark state
is heavier than the corresponding pseudoscalar state, `` eta' ''. Second, we
add a small fermion mass term. The fermion mass term breaks supersymmetry
explicitly. The vacuum degeneracy is lifted. The parity doublets split. We
evaluate the splitting. Finally, we include the theta-angle and study its
implications.Comment: LaTeX, 21 page
The generalized second law of thermodynamics of the universe bounded by the event horizon and modified gravity theories
In this paper, we investigate the validity of the generalized second law of
thermodynamics of the universe bounded by the event horizon. Here we consider
homogeneous and isotropic model of the universe filled with perfect fluid in
one case and in another case holographic model of the universe has been
considered. In the third case the matter in the universe is taken in the form
of non-interacting two fluid system as holographic dark energy and dust. Here
we study the above cases in the Modified gravity, f(R) gravity.Comment: 9 page
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