7,035 research outputs found
Quantum Dynamics of the Slow Rollover Transition in the Linear Delta Expansion
We apply the linear delta expansion to the quantum mechanical version of the
slow rollover transition which is an important feature of inflationary models
of the early universe. The method, which goes beyond the Gaussian
approximation, gives results which stay close to the exact solution for longer
than previous methods. It provides a promising basis for extension to a full
field theoretic treatment.Comment: 12 pages, including 4 figure
Magnetized Domain Walls in the Deconfined Sakai-Sugimoto Model at Finite Baryon Density
The magnetized pure pion gradient () phase in the deconfined
Sakai-Sugimoto model is explored at zero and finite temperature. We found that
the temperature has very small effects on the phase. The thermodynamical
properties of the phase shows that the excitations behave like a scalar
solitonic free particles. By comparing the free energy of the pion gradient
phase to the competing multiquark-pion gradient (MQ-) phase,
it becomes apparent that the pure pion gradient is less thermodynamically
preferred than the MQ- phase. However, in the parameter space
where the baryonic chemical potential is smaller than the onset value of the
multiquark, the dominating magnetized nuclear matter is the pion gradient
phase.Comment: 20 pages, 9 figure
Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
We analyze 24 type I X-ray bursts from GS 1826-24 observed by the Rossi X-ray
Timing Explorer between 1997 November and 2002 July. The bursts observed
between 1997-98 were consistent with a stable recurrence time of 5.74 +/- 0.13
hr. The persistent intensity of GS 1826-24 increased by 36% between 1997-2000,
by which time the burst interval had decreased to 4.10 +/- 0.08 hr. In 2002
July the recurrence time was shorter again, at 3.56 +/- 0.03 hr. The bursts
within each epoch had remarkably identical lightcurves over the full approx.
150 s burst duration; both the initial decay timescale from the peak, and the
burst fluence, increased slightly with the rise in persistent flux. The
decrease in the burst recurrence time was proportional to Mdot^(-1.05+/-0.02)
(where Mdot is assumed to be linearly proportional to the X-ray flux), so that
the ratio alpha between the integrated persistent and burst fluxes was
inversely correlated with Mdot. The average value of alpha was 41.7 +/- 1.6.
Both the alpha value, and the long burst durations indicate that the hydrogen
is burning during the burst via the rapid-proton (rp) process. The variation in
alpha with Mdot implies that hydrogen is burning stably between bursts,
requiring solar metallicity (Z ~ 0.02) in the accreted layer. We show that
solar metallicity ignition models naturally reproduce the observed burst
energies, but do not match the observed variations in recurrence time and burst
fluence. Low metallicity models (Z ~ 0.001) reproduce the observed trends in
recurrence time and fluence, but are ruled out by the variation in alpha. We
discuss possible explanations, including extra heating between bursts, or that
the fraction of the neutron star covered by the accreted fuel increases with
Mdot.Comment: 9 pages, 6 figures, accepted by ApJ. Minor revisions following the
referee's repor
Supersymmetric QCD flavor changing top quark decay
We present a detailed and complete calculation of the gluino and scalar
quarks contribution to the flavour-changing top quark decay into a charm quark
and a photon, gluon, or a Z boson within the minimal supersymmetric standard
model including flavour changing gluino-quarks-scalar quarks couplings in the
right-handed sector. We compare the results with the ones presented in an
earlier paper where we considered flavour changing couplings only in the
left-handed sector. We show that these new couplings have important
consequences leading to a large enhancement when the mixing of the scalar
partners of the left- and right-handed top quark is included. Furthermore CP
violation in the flavour changing top quark decay will occur when a SUSY phase
is taken into account.Comment: 14 pages, latex, 3 figure
High pressure study of BaFe2As2 - role of hydrostaticity and uniaxial stress
We investigate the evolution of the electrical resistivity of BaFe2As2 single
crystals with pressure. The samples used were from the same batch grown from
self flux and showed properties that were highly reproducible. Samples were
pressurised using three different pressure media: pentane-isopentane (in a
piston cylinder cell), Daphne oil (in an alumina anvil cell) and steatite (in a
Bridgman cell). Each pressure medium has its own intrinsic level of
hydrostaticity, which dramatically affects the phase diagram. An increasing
uniaxial pressure component in this system quickly reduces spin density wave
order and favours the appearance of superconductivity, similar to what is seen
in SrFe2As2.Comment: 11 page
Low energy effective action on a self-gravitating D-brane
Recently the study of braneworld on the self-gravitating D-brane has been
initiated and derived the gravitational equation on the brane by holographic
and geometrical projection methods. Surprisingly, in common with these two
methods, the matter on the brane cannot be the source of the gravity on the
brane at leading order. In this paper we will propose the low energy effective
action on the D-brane coupled with gravity which derives the same results.Comment: 8 pages, minor corrections, accepted for publication in Physical
Review
Quantum fields, cosmological constant and symmetry doubling
Energy-parity has been introduced by Kaplan and Sundrum as a protective
symmetry that suppresses matter contributions to the cosmological constant
[KS05]. It is shown here that this symmetry, schematically Energy --> - Energy,
arises in the Hilbert space representation of the classical phase space
dynamics of matter. Consistently with energy-parity and gauge symmetry, we
generalize the Liouville operator and allow a varying gauge coupling, as in
"varying alpha" or dilaton models. In this model, classical matter fields can
dynamically turn into quantum fields (Schroedinger picture), accompanied by a
gauge symmetry change -- presently, U(1) --> U(1) x U(1). The transition
between classical ensemble theory and quantum field theory is governed by the
varying coupling, in terms of a one-parameter deformation of either limit.
These corrections introduce diffusion and dissipation, leading to decoherence.Comment: Replaced by published version, no change in contents - Int. J. Theor.
Phys. (2007
A New Basis Function Approach to 't Hooft-Bergknoff-Eller Equations
We analytically and numerically investigate the 't Hooft-Bergknoff-Eller
equations, the lowest order mesonic Light-Front Tamm-Dancoff equations for
U(N_C) and SU(N_C) gauge theories. We find the wavefunction can be well
approximated by new basis functions and obtain an analytic formula for the mass
of the lightest bound state. Its value is consistent with the precedent
results.Comment: 16 pages, 3 figure
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