3,162 research outputs found
Non-minimally coupled multi-scalar black holes
We study the static, spherically symmetric black hole solutions for a
non-minimally coupled multi-scalar theory. We find numerical solutions for
values of the scalar fields when a certain constraint on the maximal charge is
satisfied. Beyond this constraint no black hole solutions exist. This
constraint therefore corresponds to extremal solutions, however, this does not
match the \kappa = 0 constraint which typically indicates extremal solutions in
other models. This implies that the set of extremal solutions have non-zero,
finite and varying surface gravity. These solutions also violate the no-hair
theorems for N>1 scalar fields and have previously been proven to be linearly
stable.Comment: 6 pages, 4 figure
Uncertain Fiscal Consolidations
The paper explores the macroeconomic consequences of fiscal consolidations whose timing and composition are uncertain. Drawing on the evidence in Alesina and Ardagna (2010), we emphasize whether or not the fiscal consolidation is driven by tax rises or expenditure cuts. We find that the composition of the fiscal consolidation, its duration, the monetary policy stance, the level of government debt and expectations over the likelihood and composition of fiscal consolidations all matter in determining the extent to which a given consolidation is expansionary and/or successful in stabilizing government debt.
Type Ia supernovae tests of fractal bubble universe with no cosmic acceleration
The unexpected dimness of Type Ia supernovae at redshifts z >~ 1 has over the
past 7 years been seen as an indication that the expansion of the universe is
accelerating. A new model cosmology, the "fractal bubble model", has been
proposed by one of us [gr-qc/0503099], based on the idea that our observed
universe resides in an underdense bubble remnant from a primordial epoch of
cosmic inflation, together with a new solution for averaging in an
inhomogeneous universe. Although there is no cosmic acceleration, it is claimed
that the luminosity distance of type Ia supernovae data will nonetheless fit
the new model, since it mimics a Milne universe at low redshifts. In this paper
the hypothesis is tested statistically against the available type Ia supernovae
data by both chi-square and Bayesian methods. While the standard model with
cosmological constant Omega_Lambda = 1-Omega_m is favoured by a Bayesian
analysis with wide priors, the comparison depends strongly on the priors chosen
for the density parameter, Omega_m. The fractal bubble model gives better
agreement generally for Omega_m<0.2. It also gives reasonably good fits for all
the range, Omega_m=0.01-0.55, allowing the possibility of a viable cosmology
with just baryonic matter, or alternatively with both baryonic matter and
additional cold dark matter.Comment: 10 pages, 5 figures, aastex. v3: Corrected volume factor changes
parameter estimates and discussion, figures redrawn, references adde
Differential approximation for Kelvin-wave turbulence
I present a nonlinear differential equation model (DAM) for the spectrum of
Kelvin waves on a thin vortex filament. This model preserves the original
scaling of the six-wave kinetic equation, its direct and inverse cascade
solutions, as well as the thermodynamic equilibrium spectra. Further, I extend
DAM to include the effect of sound radiation by Kelvin waves. I show that,
because of the phonon radiation, the turbulence spectrum ends at a maximum
frequency where
is the total energy injection rate, is the speed of sound and
is the quantum of circulation.Comment: Prepared of publication in JETP Letter
Screening and Anti-Screening Effects in J/psi Production on Nuclei
The nuclear effects in J/psi hadro- and electroproduction on nuclei are
considered in framework of reggeon approach. It is shown that screening regime
which holds for electroproduction at x_F > 0.7 and for hadroproduction at x_F >
-(0.3-0.4) is changed with anti-screening regime for smaller x_F values.Comment: 6 pages, 6 figures. Small changes in wordin
Stress corrosion in titanium alloys and other metallic materials
Multiple physical and chemical techniques including mass spectroscopy, atomic absorption spectroscopy, gas chromatography, electron microscopy, optical microscopy, electronic spectroscopy for chemical analysis (ESCA), infrared spectroscopy, nuclear magnetic resonance (NMR), X-ray analysis, conductivity, and isotopic labeling were used in investigating the atomic interactions between organic environments and titanium and titanium oxide surfaces. Key anhydrous environments studied included alcohols, which contain hydrogen; carbon tetrachloride, which does not contain hydrogen; and mixtures of alcohols and halocarbons. Effects of dissolved salts in alcohols were also studied. This program emphasized experiments designed to delineate the conditions necessary rather than sufficient for initiation processes and for propagation processes in Ti SCC
Crossing the phantom divide with k-essence in brane-worlds
We study a flat 3-brane in presence of a linear field with nonzero
cosmological constant . In this model the crossing of the phantom
divide (PD) occurs when the -essence energy density becomes negative. We
show that in the high energy regime the effective equation of state has a
resemblance of a modified Chaplygin gas while in the low energy regime it
becomes linear. We find a scale factor that begins from a singularity and
evolves to a de Sitter stable stage while other solutions have a
super-accelerated regime and end with a big rip. We use the energy conditions
to show when the effective equation of state of the brane-universe crosses the
PD.Comment: 8 pages, 5 figures. The article was fully rewritten. References
added. Accepted for publication in MPLA (2010
Dark energy from scalar field with Gauss Bonnet and non-minimal kinetic coupling
We study a model of scalar field with a general non-minimal kinetic coupling
to itself and to the curvature, and additional coupling to the Gauss Bonnet
4-dimensional invariant. The model presents rich cosmological dynamics and some
of its solutions are analyzed. A variety of scalar fields and potentials giving
rise to power-law expansion have been found. The dynamical equation of state is
studied for two cases, with and without free kinetic term . In both cases
phenomenologically acceptable solutions have been found. Some solutions
describe essentially dark energy behavior, and and some solutions contain the
decelerated and accelerated phases.Comment: 21 page
Constraining the runaway dilaton and quintessential dark energy
Dark Energy is some of the weirdest and most mysterious stuff in the universe
that tends to increase the rate of expansion of the universe. Two commonly
known forms of dark energy are the cosmological constant, a constant energy
density filling space homogeneously, and scalar fields such as quintessence or
moduli whose energy density can vary with time. We explore one particular model
for dynamic dark energy; quintessence driven by a scalar dilaton field. We
propose an ansatz for the form of the dilaton field, , where is the
scale factor and and are parameters of the model. This
phenomenological ansatz for can be motivated by generic solutions of a
scalar dilaton field in many effective string theory and string-inspired
gravity models in four dimensions. Using a compilation of current data
including type Ia supernovae, we impose observational constraints on the slope
parameters like and and then discuss the relation of our
results to analytical constrains on various cosmological parameters, including
the dark energy equation of state. Sensible constraints are imposed on model
parameters like and as well as on the dark energy/dark matter
couplings using results from structure formation. The constraints of this model
are shown to encompass the cosmological constant limit within error
bars.Comment: 32 pages, several eps figures; refs added, matches published versio
Interference in Exclusive Vector Meson Production in Heavy Ion Collisions
Photons emitted from the electromagnetic fields of relativistic heavy ions
can fluctuate into quark anti-quark pairs and scatter from a target nucleus,
emerging as vector mesons. These coherent interactions are identifiable by
final states consisting of the two nuclei and a vector meson with a small
transverse momentum. The emitters and targets can switch roles, and the two
possibilities are indistinguishable, so interference may occur. Vector mesons
are negative parity so the amplitudes have opposite signs. When the meson
transverse wavelength is larger than the impact parameter, the interference is
large and destructive.
The short-lived vector mesons decay before amplitudes from the two sources
can overlap, and so cannot interfere directly. However, the decay products are
emitted in an entangled state, and the interference depends on observing the
complete final state. The non-local wave function is an example of the
Einstein-Podolsky-Rosen paradox.Comment: 13 pages with 3 figures; submitted to Physical Review Letter
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