25,146 research outputs found
A Realistic Particle Physics Dark Energy Model
We present a realistic dark energy model derived from particle physics. Our
model has essentially no free parameters and has an equivalent fit to the
observational data (CMB, SN1a and LSS) as LCDM and a better fit than the best
effective model. With the lack of a clear determination of the
cosmological parameters theoretical considerations should be taken seriously to
distinguish between dark energy models.Comment: 5 pages, RevTex, 6 figure
Dual D-Brane Actions
Dual super Dp-brane actions are constructed by carrying out a duality
transformation of the world-volume U(1) gauge field. The resulting world-volume
actions, which contain a (p - 2)-form gauge field, are shown to have the
expected properties. Specifically, the D1-brane and D3-brane transform in ways
that can be understood on the basis of the SL(2, Z) duality of type IIB
superstring theory. Also, the D2-brane and the D4-brane transform in ways that
are expected on the basis of the relationship between type IIA superstring
theory and 11d M theory. For example, the dual D4-brane action is shown to
coincide with the double-dimensional reduction of the recently constructed
M5-brane action. The implications for gauge-fixed D-brane actions are discussed
briefly.Comment: 18 pages, latex, no figures; references adde
Low-frequency line temperatures of the CMB
Based on SU(2) Yang-Mills thermodynamics we interprete Aracde2's and the
results of earlier radio-surveys on low-frequency CMB line temperatures as a
phase-boundary effect. We explain the excess at low frequencies by evanescent,
nonthermal photon fields of the CMB whose intensity is nulled by that of Planck
distributed calibrator photons. The CMB baseline temperature thus is identified
with the critical temperature of the deconfining-preconfining transition.Comment: v2: 9 pages, 1 figure, extended discussion of why prsent photon mass
bounds are not in contradiction to a low-temperature, low-frequency Meissner
mass responsible for UEGE, matches journal versio
M(atrix) Theory on an Orbifold and Twisted Membrane
M(atrix) theory on an orbifold and classical two-branes therein are studied
with particular emphasis to heterotic M(atrix) theory on relevant to
strongly coupled heterotic and dual Type IA string theories. By analyzing
orbifold condition on Chan-Paton factors, we show that three choice of gauge
group are possible for heterotic M(atrix) theory: SO(2N), SO(2N+1) or USp(2N).
By examining area-preserving diffeomorphism that underlies the M(atrix) theory,
we find that each choices of gauge group restricts possible topologies of
two-branes. The result suggests that only the choice of SO(2N) or SO(2N+1)
groups allows open two-branes, hence, relevant to heterotic M(atrix) theory. We
show that requirement of both local vacuum energy cancellation and of
worldsheet anomaly cancellation of resulting heterotic string identifies
supersymmetric twisted sector spectra with sixteen fundamental representation
spinors from each of the two fixed points. Twisted open and closed two-brane
configurations are obtained in the large N limit.Comment: latex, 23 pages, version to appear in Nuclear Physics
Noncommutative supergeometry, duality and deformations
We introduce a notion of -algebra that can be considered as a
generalization of the notion of -manifold (a supermanifold equipped with an
odd vector field obeying ). We develop the theory of connections on
modules over -algebras and prove a general duality theorem for gauge
theories on such modules. This theorem containing as a simplest case
-duality of gauge theories on noncommutative tori can be
applied also in more complicated situations. We show that -algebras appear
naturally in Fedosov construction of formal deformation of commutative algebras
of functions and that similar -algebras can be constructed also in the case
when the deformation parameter is not formal.Comment: Extended version of hep-th/991221
A note on brane tension and M-theory
We point out that some M-theory results for brane tension can be derived from
Polchinski's formula for D-brane tension. We also argue that this formula
determines gravitational and gauge couplings in the low energy but quantum
exact effective action.Comment: 9 pages, Latex. Appendix on the resolution of an apparent conflict
with the M theory quantization result of Duff et al added. Final version to
be published in Phys. Lett.
Higher-Order Gravitational Couplings and Modular Forms in Heterotic String Compactifications
The restrictions of target--space duality are imposed at the perturbative
level on the holomorphic Wilsonian couplings that encode certain higher-order
gravitational interactions in heterotic string compactifications. A
crucial role is played by non-holomorphic corrections. The requirement of
symplectic covariance and an associated symplectic anomaly equation play an
important role in determining their form. For models which also admit a type-II
description, this equation coincides with the holomorphic anomaly equation for
type-II compactifications in the limit that a specific K\"ahler-class modulus
grows large. We explicitly evaluate some of the higher-order couplings for a
toroidal compactification with two moduli and , and we express them in
terms of modular forms.Comment: 39 pages, Late
Current distribution modelling in electroconductive fabrics
In this paper the current distribution within woven electroconductive textile sheets is investigated.The iterative method of solving very large resistor networks, which is used to model current density in textile sheets, is discussed. Factors taken into account are the conductivity of the fibres, the contact resistance between the fibres, the contact angle between the fibres and supply electrodes, as well as the size and aspect ratio of textile sheets. The influence of these factors on sheet resistivity is discussed. Maps of the current distribution generated with a computer program are included
T-duality in M-theory and supermembranes
The (q_1,q_2) SL(2,Z) string bound states of type IIB superstring theory
admit two inequivalent (T-dual) representations in eleven dimensions in terms
of a fundamental 2-brane. In both cases, the spectrum of membrane oscillations
can be determined exactly in the limit , where is the
type IIA string coupling. We find that the BPS mass formulas agree, and
reproduce the BPS mass spectrum of the string bound state. In the
non-BPS sector, the respective mass formulas apply in different corners of the
moduli space. The axiomatic requirement of T-duality in M-theory permits to
derive a discrete mass spectrum in a (thin torus) region where standard
supermembrane theory undergoes instabilities.Comment: harvmac, 9 page
Ehlers Transformations and String Effective Action
We explicitly obtain the generalization of the Ehlers transformation for
stationary axisymmetric Einstein equations to string theory. This is
accomplished by finding the twist potential corresponding to the moduli fields
in the effective two dimensional theory. Twist potential and symmetric moduli
are shown to transform under an which is a manifest symmetry of the
equations of motion. The non-trivial action of this is given by the
Ehlers transformation and belongs to the set .Comment: 13 pages, minor corrections, version to appear in Physics Letters
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