40 research outputs found
Constraints on gravity: An evidence against the covariant resolution of the Pioneer anomaly
We consider corrections in the form of to the
Einstein-Hilbert Lagrangian. Then we compute the corrections to the
Schwarszchild geometry due to the inclusion of this general term to the
Lagrangian. We show that
gives rise to a constant anomalous acceleration for objects orbiting the Sun
onward the Sun. This leads to the conclusion that would have covariantly
resolved the Pioneer anomaly if this value of had not
contradicted other observations.
We notice that the experimental bounds on grows stronger in case
we examine the deformation of the space-time geometry around objects lighter
than the Sun. We therefore use the high precision measurements around the Earth
(LAGEOS and LLR) and obtain a very strong constraint on the corrections in the
form of and in particular . This bound requires
.
Therefore it refutes the covariant resolution of the Pioneer anomaly.Comment: ...v5: references added, new discussions adde
The world-sheet corrections to dyons in the Heterotic theory
All the linear alpha-prime corrections, however excluding the gravitational
Chern-Simons correction, are studied in the toroidally compactified critical
Heterotic string theory. These corrections are computed to the entropy for a
BPS static spherical four dimensional dyonic black hole which represents a
wrapped fundamental string carrying arbitrary winding and momentum charges
along one cycle in the presence of KK-monopole and H-monopole charges
associated to another cycle. It is verified that after the inclusion of the
gravitational Chern-Simons corrections [hep-th/0608182], all the linear
alpha-prime corrections to the entropy for the supersymmetric dyon can be
reproduced by the inclusion of only the Gauss-Bonnet Lagrangian to the
supergravity approximation of the induced Lagrangian.Comment: JHEP style, 17 Pages; v2: a typo corrected ; v3: The coupling of the
gravitational Chern-Simons terms to the three form field strength taken into
account. The conclusion correcte
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
The alpha-prime stretched horizon in the Heterotic string
The linear alpha-prime corrections and the field redefinition ambiguities are
studied for half-BPS singular backgrounds representing a wrapped fundamental
string. It is showed that there exist schemes in which the inclusion of all the
linear alpha-prime corrections converts these singular solutions to black holes
with a regular horizon for which the modified Hawking-Bekenstein entropy is in
agreement with the statistical entropy.Comment: 22 pages JHEP; new discussions and more details added to section
How Does a Fundamental String Stretch its Horizon?
It has recently been shown that if we take into account a class of higher
derivative corrections to the effective action of heterotic string theory, the
entropy of the black hole solution representing elementary string states
correctly reproduces the statistical entropy computed from the degeneracy of
elementary string states. So far the form of the solution has been analyzed at
distance scales large and small compared to the string scale. We analyze the
solution that interpolates between these two limits and point out a subtlety in
constructing such a solution due to the presence of higher derivative terms in
the effective action. We also study the T-duality transformation rules to
relate the moduli fields of the effective field theory to the physical
compactification radius in the presence of higher derivative corrections and
use these results to find the physical radius of compactification near the
horizon of the black hole. The radius approaches a finite value even though the
corresponding modulus field vanishes. Finally we discuss the non-leading
contribution to the black hole entropy due to space-time quantum corrections to
the effective action and the ambiguity involved in comparing this result to the
statistical entropy.Comment: LaTeX file, 38 pages; v2: minor changes and added reference
Triangular Ring Resonator: Direct measurement of the parity-odd parameters of the photon sector of SME
We introduce the the Triangular Ring (TR) resonator. We show that the
difference between the clockwise and anti-clockwise resonant frequencies of a
vacuum TR resonator is sensitive to the birefringence parity-odd parameters of
the photon's sector of the minimal Standard Model Extension (mSME): the
Standard Model plus all the perturbative parameters encoding the break the
Lorentz symmetry. We report that utilizing the current technology allows for
direct measurement of these parameters with a sensitivity of the parity even
ones and improves the best current resonator bounds by couple of orders of
magnitudes.
We note that designing an optical table that rotates perpendicular to the
gravitational equipotential surface (geoid) allows for direct measurement of
the constancy of the light speed at the vicinity of the earth in all directions
in particular perpendicular to the geoid. If this table could achieve the
precision of the ordinary tables, then it would improve the GPS bounds on the
constancy of the light speed perpendicular to geoid by about eight orders of
magnitude.Comment: ref. added, minor corrections, matches the published versio
Entropy Function for Heterotic Black Holes
We use the entropy function formalism to study the effect of the Gauss-Bonnet
term on the entropy of spherically symmetric extremal black holes in heterotic
string theory in four dimensions. Surprisingly the resulting entropy and the
near horizon metric, gauge field strengths and the axion-dilaton field are
identical to those obtained by Cardoso et. al. for a supersymmetric version of
the theory that contains Weyl tensor squared term instead of the Gauss-Bonnet
term. We also study the effect of holomorphic anomaly on the entropy using our
formalism. Again the resulting attractor equations for the axion-dilaton field
and the black hole entropy agree with the corresponding equations for the
supersymmetric version of the theory. These results suggest that there might be
a simpler description of supergravity with curvature squared terms in which we
supersymmetrize the Gauss-Bonnet term instead of the Weyl tensor squared term.Comment: LaTeX file, 23 pages; v2: references added; v3: minor addition; v4:
minor change
Dyon Spectrum in N=4 Supersymmetric Type II String Theories
We compute the spectrum of quarter BPS dyons in freely acting Z_2 and Z_3
orbifolds of type II string theory compactified on a six dimensional torus. For
large charges the result for statistical entropy computed from the degeneracy
formula agrees with the corresponding black hole entropy to first non-leading
order after taking into account corrections due to the curvature squared terms
in the effective action. The result is significant since in these theories the
entropy of a small black hole, computed using the curvature squared corrections
to the effective action, fails to reproduce the statistical entropy associated
with elementary string states.Comment: LaTeX file, 32 pages; v2:minor change
String Theory Effects on Five-Dimensional Black Hole Physics
We review recent developments in understanding quantum/string corrections to
BPS black holes and strings in five-dimensional supergravity. These objects are
solutions to the effective action obtained from M-theory compactified on a
Calabi-Yau threefold, including the one-loop corrections determined by anomaly
cancellation and supersymmetry. We introduce the off-shell formulation of this
theory obtained through the conformal supergravity method and review the
methods for investigating supersymmetric solutions. This leads to
quantum/string corrected attractor geometries, as well as asymptotically flat
black strings and spinning black holes. With these solutions in hand, we
compare our results with analogous studies in four-dimensional string-corrected
supergravity, emphasizing the distinctions between the four and five
dimensional theories.Comment: 85 pages; uses ws-ijmpa-mod.cls article class; Invited review for
IJMP