35,537 research outputs found
Remarks on the Classical Size of D-Branes
We discuss different criteria for `classical size' of extremal Dirichlet
p-branes in type-II supergravity. Using strong-weak coupling duality, we find
that the size of the strong-coupling region at the core of the (p<3)-branes, is
always given by the asymptotic string scale, if measured in the weakly coupled
dual string metric. We also point out how the eleven-dimensional Planck scale
arises in the classical 0-brane solution, as well as the ten-dimensional Planck
scale in the D-instanton solution.Comment: 8 pp, harvma
Galois covers of the open p-adic disc
This paper investigates Galois branched covers of the open -adic disc and
their reductions to characteristic . Using the field of norms functor of
Fontaine and Wintenberger, we show that the special fiber of a Galois cover is
determined by arithmetic and geometric properties of the generic fiber and its
characteristic zero specializations. As applications, we derive a criterion for
good reduction in the abelian case, and give an arithmetic reformulation of the
local Oort Conjecture concerning the liftability of cyclic covers of germs of
curves.Comment: 19 pages; substantial organizational and expository changes; this is
the final version corresponding to the official publication in Manuscripta
Mathematica; abstract update
High-field noise in metallic diffusive conductors
We analyze high-field current fluctuations in degenerate conductors by
mapping the electronic Fermi-liquid correlations at equilibrium to their
semiclassical non-equilibrium form. Our resulting Boltzmann description is
applicable to diffusive mesoscopic wires. We derive a non-equilibrium
connection between thermal fluctuations of the current and resistive
dissipation. In the weak-field limit this is the canonical fluctuation-
dissipation theorem. Away from equilibrium, the connection enables explicit
calculation of the excess ``hot-electron'' contribution to the thermal
spectrum. We show that excess thermal noise is strongly inhibited by Pauli
exclusion. This behaviour is generic to the semiclassical metallic regime.Comment: 13 pp, one fig. Companion paper to cond-mat/9911251. Final version,
to appear in J. Phys.: Cond. Ma
Space-time symplectic extension
It is conjectured that in the origin of space-time there lies a symplectic
rather than metric structure. The complex symplectic symmetry Sp(2l,C), l\ge1
instead of the pseudo-orthogonal one SO(1,d-1), d\ge4 is proposed as the
space-time local structure group. A discrete sequence of the metric space-times
of the fixed dimensionalities d=(2l)^2 and signatures, with l(2l-1) time-like
and l(2l+1) space-like directions, defined over the set of the Hermitian
second-rank spin-tensors is considered as an alternative to the
pseudo-Euclidean extra dimensional space-times. The basic concepts of the
symplectic framework are developed in general, and the ordinary and
next-to-ordinary space-time cases with l=1,2, respectively, are elaborated in
more detail. In particular, the scheme provides the rationale for the
four-dimensionality and 1+3 signature of the ordinary space-time.Comment: 15 pp, LaTe
On certain other sets of integers
We show that if A is a subset of {1,...,N} containing no non-trivial
three-term arithmetic progressions then |A|=O(N/ log^{3/4-o(1)} N).Comment: 29 pp. Corrected typos. Added definitions for some non-standard
notation and remarks on lower bound
Three Generations of SUSY Standard Model of Nambu-Goto String
A four dimensional Superstring is constructed starting from a twenty six
dimensional bosonic string. Fermions are introduced by noting the Manselstam's
proof of equivalence of two fermions to one boson in 1+1 dimensions. The action
of the superstring is invariant under SO(6) SO(5). It has four bosonic
coordinates and twenty four Majorana fermions of SO(3,1) representing two
transverse modes of super fermions and conformal ghosts (b,c). The super
conformal ghosts () are the quanta of an extended Hilbert space
of the remaining longitudinal modes of two superfermions. The massless spectrum
obtained by quantising the action, contain vector mesons which are generators
of the SO(6)SO(5). Using Wilson loops, this product group is proven to
descend to without breaking
supersymmetry.Thus there are just three generations of quarks and leptons.Comment: 11 page
Spectral analysis and abundances of the post-HB star HD 76431
HD76431 is a slow rotating post-HB star that shows an underabundance of
helium by 0.5 dex relative to the solar value. These observational facts
suggest that atomic diffusion could be active in its atmosphere. We have used
the MMT and Bok spectra to estimate the atmospheric parameters of the target
star using the model atmospheres and synthetic spectra calculated with TLUSTY
and SYNSPEC. The derived values of the effective temperature, surface gravity,
helium abundance are consistent with those obtained by Ramspeck et al. (2001b).
It appears that NLTE effect are not important for HD76431. We have used Stokes
I spectra from ESPaDOnS at CFHT to perform an abundance analysis and a search
for observational evidence of vertical stratification of the abundance of
certain elements. The results of our abundance analysis are in good agreement
with previously published data with respect to average abundances. Our
numerical simulations show that carbon and nitrogen reveal signatures of
vertical abundance stratification in the atmosphere of HD76431. It appears that
the carbon abundance increases toward the deeper atmospheric layers. Nitrogen
also shows a similar behaviour, but in deeper atmospheric layers we obtain a
significant dispersion for the estimates of its abundance. To our knowledge,
this is the first demonstration of vertical abundance stratification of metals
in a post-HB star and up to now it is the hottest star to show such
stratification features. We also report the detection of two SiIII and one
TiIII emission lines in the spectra of HD76431 that were not detected in
previous studies.Comment: 7 pages, 5 figures, accepted for publication in MNRA
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