7,980 research outputs found
General Static N=2 Black Holes
We find general static BPS black hole solutions for general N=2, d=4
supergravity theories with an arbitrary number of vector multiplets. These
solutions are completely specified by the K\"ahler potential of the underlying
special K\"ahler geometry and a set of constrained harmonic functions.Comment: Latex, 7 pages, typos corrected, version to appear in MPL
Axion Couplings and Effective Cut-Offs in Superstring Compactifications
We use the linear supermultiplet formalism of supergravity to study axion
couplings and chiral anomalies in the context of field-theoretical Lagrangians
describing orbifold compactifications beyond the classical approximation. By
matching amplitudes computed in the effective low energy theory with the
results of string loop calculations we determine the appropriate counterterm in
this effective theory that assures modular invariance to all loop order. We use
supersymmetry consistency constraints to identify the correct ultra-violet
cut-offs for the effective low energy theory. Our results have a simple
interpretation in terms of two-loop unification of gauge coupling constants at
the string scale.Comment: 25 page
On the Stability of Non-Supersymmetric Quantum Attractors in String Theory
We study four dimensional non-supersymmetric attractors in type IIA string
theory in the presence of sub-leading corrections to the prepotential. For a
given Calabi-Yau manifold, the D0-D4 system admits an attractor point in the
moduli space which is uniquely specified by the black hole charges. The
perturbative corrections to the prepotential do not change the number of
massless directions in the black hole effective potential. We further study
non-supersymmetric D0-D6 black holes in the presence of sub-leading
corrections. In this case the space of attractor points define a hypersurface
in the moduli space.Comment: References Added, Typos Corrected, Appendix A.2 Reordere
Measuring patchy reionisation with kSZ-21 cm correlations
We study cross-correlations of the kinetic Sunyaev-Zel'dovich effect (kSZ)
and 21 cm signals during the epoch of reionisation (EoR) to measure the effects
of patchy reionisation. Since the kSZ effect is proportional to the
line-of-sight velocity, the kSZ-21 cm cross correlation suffers from
cancellation at small angular scales. We thus focus on the correlation between
the kSZ-squared field (kSZ) and 21 cm signals. When the global ionisation
fraction is low (), the kSZ fluctuation is dominated by
rare ionised bubbles which leads to an anti-correlation with the 21 cm signal.
When , the correlation is dominated by small pockets of
neutral regions, leading to a positive correlation. However, at very high
redshifts when , the spin temperature fluctuations change the sign of
the correlation from negative to positive, as weakly ionised regions can have
strong 21 cm signals in this case. To extract this correlation, we find that
Wiener filtering is effective in removing large signals from the primary CMB
anisotropy. The expected signal-to-noise ratios for a 10-hour integration
of upcoming Square Kilometer Array data cross-correlated with maps from the
current generation of CMB observatories with 3.4~K arcmin noise and
1.7~arcmin beam over 100~deg are 51, 60, and 37 for , 0.5, and
0.9, respectively.Comment: 7pages, 7 figure
Non-Supersymmetric Stringy Attractors
In this paper we examine the stability of non-supersymmetric attractors in
type IIA supergravity compactified on a Calabi-Yau manifold, in the presence of
sub-leading corrections to the N=$ pre-potential. We study black hole
configurations carrying D0-D6 and D0-D4 charges. We consider the O(1)
corrections to the pre-potential given by the Euler number of the Calabi-Yau
manifold. We argue that such corrections in general can not lift the zero modes
for the D0-D6 attractors. However, for the attractors carrying the D0-D4
charges, they affect the zero modes in the vector multiplet sector. We show
that, in the presence of such O(1) corrections, the D0-D4 attractors can either
be stable or unstable depending on the geometry of the underlying Calabi-Yau
manifold, and on the specific values of the charges they carry.Comment: corrected typos, minor modification
Cosmological Conductive/Cooling Fronts as Lyman Alpha Forest Clouds
We propose a simple model for the origin and evolution of \lya clouds based
on cosmological conductive/cooling fronts. In this model the \lya arises in the
interfaces between the IGM and cold clouds that could be tentatively identified
with protogalaxies. Most of the properties of the \lya absorbers are reproduced
with a very restricted number of assumptions. Among these are the correct range
of HI column density, cloud sizes and redshift and HI column density
distributions for the absorbers. Several predictions and implications of the
model are briefly discussed.Comment: 9 pages, plain TeX, 3 figures; ApJ Letters, accepte
Reionization constraints on primordial magnetic fields
We study the impact of the extra density fluctuations induced by primordial
magnetic fields on the reionization history in the redshift range: . We perform a comprehensive MCMC physical analysis allowing the variation
of parameters related to primordial magnetic fields (strength, , and
power-spectrum index ), reionization, and
CDM cosmological model. We find that magnetic field strengths in the
range: nG (for nearly scale-free power spectra) can
significantly alter the reionization history in the above redshift range and
can relieve the tension between the WMAP and quasar absorption spectra data.
Our analysis puts upper-limits on the magnetic field strength nG (95 % c.l.) for , respectively. These represent the strongest magnetic field constraints
among those available from other cosmological observables.Comment: Accepted for publication in MNRAS; 9 pages, 6 figure
Static N=2 Black Holes For Quadratic Prepotentials
We employ the principle of minimal central charge and study the entropy of
N=2 black holes corresponding to the most general quadratic prepotential. We
also give a static black hole solution for these models in which the scalar
moduli are non constants. Finally, we speculate on the microscopic origin for
our solution.Comment: 8 pages, Latex fil
Duality Symmetries in N=2 Heterotic Superstring
We review the derivation and the basic properties of the perturbative
prepotential in N=2 compactifications of the heterotic superstring. We discuss
the structure of the perturbative monodromy group and the embedding of rigidly
supersymmetric monodromies associated with enhanced gauge groups, at both
perturbative and non-perturbative level.Comment: Based on talks presented at several conferences. 12 pages, LaTe
Partial Breaking of N=2 Supersymmetry and Decoupling Limit of Nambu-Goldstone Fermion in U(N) Gauge Model
We study the N=1 U(N) gauge model obtained by spontaneous breaking of N=2
supersymmetry. The Fayet-Iliopoulos term included in the N=2 action does not
appear in the action on the N=1 vacuum and the superpotential is modified to
break discrete R symmetry. We take a limit in which the Kahler metric becomes
flat and the superpotential preserves non-trivial form. The Nambu-Goldstone
fermion is decoupled from other fields but the resulting action is still N=1
supersymmetric. It shows the origin of the fermionic shift symmetry in N=1 U(N)
gauge theory.Comment: 10 pages,revised version to appear in Nuclear Physics
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