927 research outputs found
Quadratic alpha' corrections to T-duality
The quadratic alpha' corrections to the two-dimensional black hole and to its
T-dual are calculated. These backgrounds are used to write the covariant form
of the quadratic alpha' corrections to the T-duality for general time-dependent
backgrounds of dilaton and diagonal metric in the bosonic string theory.Comment: 15 pages, JHEP; typos corrected, references adde
Observations on intergeneric hybrids in tilapias
Hybridization, Growth, Sex ratio, Reproduction, Reproductive behaviour Tilapia zillii, Oreochromis andersonii, Oreochromis aureus, Oreochromis macrochir, Oreochromis mortimeri, Oreochromis mossambicus, Oreochromis niloticus, Oreochromis placidus, Oreochromis spilurus, Oreochromis tanganicae, Sarotherodon galilaeus
Cosmology as Geodesic Motion
For gravity coupled to N scalar fields with arbitrary potential V, it is
shown that all flat (homogeneous and isotropic) cosmologies correspond to
geodesics in an (N+1)-dimensional `augmented' target space of Lorentzian
signature (1,N), timelike if V>0, null if V=0 and spacelike if V<0.
Accelerating cosmologies correspond to timelike geodesics that lie within an
`acceleration subcone' of the `lightcone'. Non-flat (k=-1,+1) cosmologies are
shown to evolve as projections of geodesic motion in a space of dimension
(N+2), of signature (1,N+1) for k=-1 and signature (2,N) for k=+1. This
formalism is illustrated by cosmological solutions of models with an
exponential potential, which are comprehensively analysed; the late-time
behviour for other potentials of current interest is deduced by comparison.Comment: 26 pages, 2 figures, journal version with additional reference
Fingerprinting Hysteresis
We test the predictive power of first-oder reversal curve (FORC) diagrams
using simulations of random magnets. In particular, we compute a histogram of
the switching fields of the underlying microscopic switching units along the
major hysteresis loop, and compare to the corresponding FORC diagram. We find
qualitative agreement between the switching-field histogram and the FORC
diagram, yet differences are noticeable. We discuss possible sources for these
differences and present results for frustrated systems where the discrepancies
are more pronounced.Comment: 4 pages, 5 figure
Massive motion in Brans-Dicke geometry and beyond
Gravity theories that can be viewed as dynamics for area metric manifolds,
for which Brans-Dicke theory presents a recently studied example, require for
their physical interpretation the identification of the distinguished curves
that serve as the trajectories of light and massive matter. Complementing
previous results on the propagation of light, we study effective massive point
particle motion. We show that the relevant geometrical structure is a special
Finsler norm determined by the area metric, and that massive point particles
follow Finsler geodesics.Comment: 12 page
Exact solution of scalar field cosmology with exponential potentials and transient acceleration
We show that the general solution of scalar field cosmology in dimensions
with exponential potentials for flat Robertson-Walker metric can be found in a
straightforward way by introducing new variables which completely decouple the
system. The explicit solution shows the region of parameters where the
expansion has eternal acceleration, transient periods of acceleration, or no
period of acceleration at all. In the cases of transient acceleration, the
energy density exhibits a plateau during the accelerated expansion, where
, due to dominance of potential energy. We determine the interval
of accelerated expansion in terms of a simple formula. In particular, it shows
that the period of accelerated expansion decreases in higher dimensions.Comment: 6 pages, latex, 1 figure, references adde
Determinant-Gravity: Cosmological implications
We analyze the action as a possible alternative or addition to the Einstein gravity.
Choosing a particular form of we can restore the
Einstein gravity and, if , we obtain the cosmological constant
term. Taking and expanding the action in , we obtain as a leading term the Einstein Lagrangian with a cosmological
constant proportional to and a series of higher order operators. In
general case of non-vanishing and new cosmological
solutions for the Robertson-Walker metric are obtained.Comment: revtex format, 5 pages,8 figures,references adde
Studies on the Weak Itinerant Ferromagnet SrRuO3 under High Pressure to 34 GPa
The dependence of the Curie temperature Tc on nearly hydrostatic pressure has
been determined to 17.2 GPa for the weak itinerant ferromagnetic SrRuO3 in both
polycrystalline and single-crystalline form. Tc is found to decrease under
pressure from 162 K to 42.7 K at 17.2 GPa in nearly linear fashion at the rate
dTc/dP = -6.8 K/GPa. No superconductivity was found above 4 K in the pressure
range 17 to 34 GPa. Room-temperature X-ray diffraction studies to 25.3 GPa
reveal no structural phase transition but indicate that the average Ru-O-Ru
bond angle passes through a minimum near 15 GPa. The bulk modulus and its
pressure derivative were determined to be B =192(3) GPa and B' = 5.0(3),
respectively. Parallel ac susceptibility studies on polycrystalline CaRuO3 at 6
and 8 GPa pressure found no evidence for either ferromagnetism or
superconductivity above 4 K
Gravity a la Born-Infeld
A simple technique for the construction of gravity theories in Born-Infeld
style is presented, and the properties of some of these novel theories are
investigated. They regularize the positive energy Schwarzschild singularity,
and a large class of models allows for the cancellation of ghosts. The possible
correspondence to low energy string theory is discussed. By including curvature
corrections to all orders in alpha', the new theories nicely illustrate a
mechanism that string theory might use to regularize gravitational
singularities.Comment: 21 pages, 2 figures, new appendix B with corrigendum: Class. Quantum
Grav. 21 (2004) 529
Radiation-dominated area metric cosmology
We provide further crucial support for a refined, area metric structure of
spacetime. Based on the solution of conceptual issues, such as the consistent
coupling of fermions and the covariant identification of radiation fields on
area metric backgrounds, we show that the radiation-dominated epoch of area
metric cosmology is equivalent to that epoch in standard Einstein cosmology.
This ensures, in particular, successful nucleosynthesis. This surprising result
complements the previously derived prediction of a small late-time acceleration
of an area metric universe.Comment: 23 pages, no figures; references adde
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