1,103 research outputs found
Oblique triangular antiferromagnetic phase in CsCuCoCl
The spin-1/2 stacked triangular antiferromagnet CsCuCoCl with
undergoes two phase transitions at zero field. The
low-temperature phase is produced by the small amount of Co doping. In
order to investigate the magnetic structures of the two ordered phases, the
neutron elastic scattering experiments have been carried out for the sample
with . It is found that the intermediate phase is identical to
the ordered phase of CsCuCl, and that the low-temperature phase is an
oblique triangular antiferromagnetic phase in which the spins form a triangular
structure in a plane tilted from the basal plane. The tilting angle which is
42 at K decreases with increasing temperature, and becomes
zero at K. An off-diagonal exchange term is proposed as the
origin of the oblique phase.Comment: 6 pages, 7 figure
Domain Bubbles of Extra Dimensions
``Dimension bubbles'' of the type previously studied by Blau and Guendelman
[S.K. Blau and E.I. Guendelman, Phys. Rev. D40, 1909 (1989)], which effectively
enclose a region of 5d spacetime and are surrounded by a region of 4d
spacetime, can arise in a 5d theory with a compact extra dimension that is
dimensionally reduced to give an effective 4d theory. These bubbles with thin
domain walls can be stabilized against total collapse in a rather natural way
by a scalar field which, as in the case with ``ordinary'' nontopological
solitons, traps light scalar particles inside the bubble.Comment: 13 pages, no figures; to appear in Phys.Rev.
Effect of maternal restraint stress during gestation on temporal lipopolysaccharide-induced neuroendocrine and immune responses of progeny
The impact of gestational dam restraint stress on progeny immune and neuroendocrine temporal hormone responses to lipopolysaccharide (LPS) challenge was assessed. Maternal stress (5-min snout snare restraint stress during days 84 to 112 of gestation) increased (P \u3c 0.05) the magnitude of tumor necrosis factor (TNF)-α, interleukin-6, epinephrine (E), norepinephrine, and serum amyloid A (SAA) production following LPS infusion in the offspring. Moreover, these effects appear to be dependent on gender for TNF-α, E, and cortisol production. However, maternal stress did not affect (P \u3c 0.05) the normalization of proinflammatory cytokines or neuroendocrine hormones produced following LPS. Collectively, these results indicate that maternal stress impacts aspects of the proinflammatory cytokine and stress hormone response in their progeny following LPS dosing of the offspring. This response is potentially responsible in part for the resultant changes to SAA production. Because several of the changes observed here are dependent on pig gender, these results are also the first evidence that inherent epigenetic factors coupled with maternal stress impact the cumulative response to stress and LPS in young pigs
Newton's Second Law in a Noncommutative Space
In this work we show that corrections to the Newton's second law appears if
we assume that the phase space has a symplectic structure consistent with the
rules of commutation of noncommutative quantum mechanis. In the central field
case we find that the correction term breaks the rotational symmetry. In
particular, for the Kepler problem, this term takes the form of a Coriolis
force produced by the weak gravitational field far from a rotating massive
object.Comment: 7 pages, References adde
Remarks on the Causality, Unitarity and Supersymmetric Extension of the Lorentz and CPT-Violating Maxwell-Chern-Simons Model
The gauge-invariant Chern-Simons-type Lorentz- and CPT-breaking term is here
re-assessed and issues like causality, unitarity, spontaneous gauge-symmetry
breaking are investigated. Moreover, we obtain a minimal extension of such a
system to a supersymmetric environment. We comment on resulting peculiar
self-couplings for the gauge sector, as well as on background contribution for
gaugino masses.Comment: 5 pages, NPB style, talk presented at "Renormalization Group and
Anomalies in Gravity and Cosmology", Ouro Preto, Brazil, March 200
Model for a Universe described by a non-minimally coupled scalar field and interacting dark matter
In this work it is investigated the evolution of a Universe where a scalar
field, non-minimally coupled to space-time curvature, plays the role of
quintessence and drives the Universe to a present accelerated expansion. A
non-relativistic dark matter constituent that interacts directly with dark
energy is also considered, where the dark matter particle mass is assumed to be
proportional to the value of the scalar field. Two models for dark matter
pressure are considered: the usual one, pressureless, and another that comes
from a thermodynamic theory and relates the pressure with the coupling between
the scalar field and the curvature scalar. Although the model has a strong
dependence on the initial conditions, it is shown that the mixture consisted of
dark components plus baryonic matter and radiation can reproduce the expected
red-shift behavior of the deceleration parameter, density parameters and
luminosity distance.Comment: 11 pages and 6 figures. To appear in GR
Out of equilibrium: understanding cosmological evolution to lower-entropy states
Despite the importance of the Second Law of Thermodynamics, it is not
absolute. Statistical mechanics implies that, given sufficient time, systems
near equilibrium will spontaneously fluctuate into lower-entropy states,
locally reversing the thermodynamic arrow of time. We study the time
development of such fluctuations, especially the very large fluctuations
relevant to cosmology. Under fairly general assumptions, the most likely
history of a fluctuation out of equilibrium is simply the CPT conjugate of the
most likely way a system relaxes back to equilibrium. We use this idea to
elucidate the spacetime structure of various fluctuations in (stable and
metastable) de Sitter space and thermal anti-de Sitter space.Comment: 27 pages, 11 figure
Gauged Dimension Bubbles
Some of the peculiar electrodynamical effects associated with gauged
``dimension bubbles'' are presented. Such bubbles, which effectively enclose a
region of 5d spacetime, can arise from a 5d theory with a compact extra
dimension. Bubbles with thin domain walls can be stabilized against total
collapse by the entrapment of light charged scalar bosons inside the bubble,
extending the idea of a neutral dimension bubble to accommodate the case of a
gauged U(1) symmetry. Using a dielectric approach to the 4d dilaton-Maxwell
theory, it is seen that the bubble wall is almost totally opaque to photons,
leading to a new stabilization mechanism due to trapped photons. Photon
dominated bubbles very slowly shrink, resulting in a temperature increase
inside the bubble. At some critical temperature, however, these bubbles
explode, with a release of radiation.Comment: 14 pages, no figures; to appear in Phys.Rev.
Wave propagation in axion electrodynamics
In this paper, the axion contribution to the electromagnetic wave propagation
is studied. First we show how the axion electrodynamics model can be embedded
into a premetric formalism of Maxwell electrodynamics. In this formalism, the
axion field is not an arbitrary added Chern-Simon term of the Lagrangian, but
emerges in a natural way as an irreducible part of a general constitutive
tensor.We show that in order to represent the axion contribution to the wave
propagation it is necessary to go beyond the geometric approximation, which is
usually used in the premetric formalism. We derive a covariant dispersion
relation for the axion modified electrodynamics. The wave propagation in this
model is studied for an axion field with timelike, spacelike and null
derivative covectors. The birefringence effect emerges in all these classes as
a signal of Lorentz violation. This effect is however completely different from
the ordinary birefringence appearing in classical optics and in premetric
electrodynamics. The axion field does not simple double the ordinary light cone
structure. In fact, it modifies the global topological structure of light cones
surfaces. In CFJ-electrodynamics, such a modification results in violation of
causality. In addition, the optical metrics in axion electrodynamics are not
pseudo-Riemannian. In fact, for all types of the axion field, they are even
non-Finslerian
Friedmann-like equations for High Energy Area of Universe
In this paper, evolution of the high energy area of universe, through the
scenario of 5 dimensional (5D) universe, has been studied. For this purpose, we
solve Einstein equations for 5D metric and 5D perfect fuid to derive
Friedmann-like equations. Then we obtain the evolution of scale factor and
energy density with respect to both space-like and time-like extra dimensions.
We obtain the novel equations for the space-like extra dimension and show that
the matter with zero pressure cannot exist in the bulk. Also, for dark energy
fuid and vacuum fluid, we have both accelerated expansion and contraction in
the bulk.Comment: 9 pages, Accepted to publication in IJTP 26 June 2012. arXiv admin
note: substantial text overlap with arXiv:1202.497
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