6,144 research outputs found
Brane Gas Inflation
We consider the brane gas picture of the early universe. At later stages,
when there are no winding modes and the background is free to expand, we show
that a moving 3-brane, which we identify with our universe, can inflate even
though it is radiation-dominated. The crucial ingredients for successful
inflation are the coupling to the dilaton and the equation of state of the
bulk. If we suppose the brane initially forms in a collision of
higher-dimensional branes, then the spectrum of primordial density fluctuations
naturally has a thermal origin.Comment: 4 pages, 1 figur
Development of uniform and predictable battery materials for nickel cadmium aerospace cells Quarterly report, 8 Aug. - 7 Nov. 1968
Sintering of carbonyl nickel powders for nickel cadmium batteries fabricatio
Two-point correlations of the Gaussian symplectic ensemble from periodic orbits
We determine the asymptotics of the two-point correlation function for
quantum systems with half-integer spin which show chaotic behaviour in the
classical limit using a method introduced by Bogomolny and Keating [Phys. Rev.
Lett. 77 (1996) 1472-1475]. For time-reversal invariant systems we obtain the
leading terms of the two-point correlation function of the Gaussian symplectic
ensemble. Special attention has to be paid to the role of Kramers' degeneracy.Comment: 7 pages, no figure
Making sense of the divergent series for reconstructing a Hamiltonian from its eigenstates and eigenvalues
In quantum mechanics the eigenstates of the Hamiltonian form a complete
basis. However, physicists conventionally express completeness as a formal sum
over the eigenstates, and this sum is typically a divergent series if the
Hilbert space is infinite dimensional. Furthermore, while the Hamiltonian can
be reconstructed formally as a sum over its eigenvalues and eigenstates, this
series is typically even more divergent. For the simple cases of the
square-well and the harmonic-oscillator potentials this paper explains how to
use the elementary procedure of Euler summation to sum these divergent series
and thereby to make sense of the formal statement of the completeness of the
formal sum that represents the reconstruction of the Hamiltonian.Comment: 5 pages, version to appear in American Journal of Physic
Renormalisation group determination of the order of the DNA denaturation transition
We report on the nature of the thermal denaturation transition of homogeneous
DNA as determined from a renormalisation group analysis of the
Peyrard-Bishop-Dauxois model. Our approach is based on an analogy with the
phenomenon of critical wetting that goes further than previous qualitative
comparisons, and shows that the transition is continuous for the average
base-pair separation. However, since the range of universal critical behaviour
appears to be very narrow, numerically observed denaturation transitions may
look first-order, as it has been reported in the literature.Comment: 6 pages; no figures; to appear in Europhysics Letter
Late time evolution of brane gas cosmology and compact internal dimensions
We study the late-time behavior of a universe in the framework of brane gas
cosmology. We investigate the evolution of a universe with a gas of
supergravity particles and a gas of branes. Considering the case when different
dimensions are anisotropically wrapped by various branes, we have derived
Friedman-like equations governing the dynamics of wrapped and unwrapped
subvolumes. We point out that the compact internal dimensions are wrapped by
three or higher dimensional branes.Comment: 16 pages, typos, references, comment on the possibility of
stabilizing the internal dimensions with fluxe
Semiclassical form factor for spectral and matrix element fluctuations of multi-dimensional chaotic systems
We present a semiclassical calculation of the generalized form factor which
characterizes the fluctuations of matrix elements of the quantum operators in
the eigenbasis of the Hamiltonian of a chaotic system. Our approach is based on
some recently developed techniques for the spectral form factor of systems with
hyperbolic and ergodic underlying classical dynamics and f=2 degrees of
freedom, that allow us to go beyond the diagonal approximation. First we extend
these techniques to systems with f>2. Then we use these results to calculate
the generalized form factor. We show that the dependence on the rescaled time
in units of the Heisenberg time is universal for both the spectral and the
generalized form factor. Furthermore, we derive a relation between the
generalized form factor and the classical time-correlation function of the Weyl
symbols of the quantum operators.Comment: some typos corrected and few minor changes made; final version in PR
Periodic-Orbit Theory of Universality in Quantum Chaos
We argue semiclassically, on the basis of Gutzwiller's periodic-orbit theory,
that full classical chaos is paralleled by quantum energy spectra with
universal spectral statistics, in agreement with random-matrix theory. For
dynamics from all three Wigner-Dyson symmetry classes, we calculate the
small-time spectral form factor as power series in the time .
Each term of that series is provided by specific families of pairs of
periodic orbits. The contributing pairs are classified in terms of close
self-encounters in phase space. The frequency of occurrence of self-encounters
is calculated by invoking ergodicity. Combinatorial rules for building pairs
involve non-trivial properties of permutations. We show our series to be
equivalent to perturbative implementations of the non-linear sigma models for
the Wigner-Dyson ensembles of random matrices and for disordered systems; our
families of orbit pairs are one-to-one with Feynman diagrams known from the
sigma model.Comment: 31 pages, 17 figure
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