106 research outputs found
Degeneracy of Decadent Dyons
A quarter-BPS dyon in super Yang-Mills theory is generically
`decadent' in that it is stable only in some regions of the moduli space and
decays on submanifolds in the moduli space. Using this fact, and from the
degeneracy of the system close to the decay, a new derivation for the
degeneracy of such dyons is given. The degeneracy obtained from these very
simple physical considerations is in precise agreement with the results
obtained from index computations in all known cases. Similar considerations
apply to dyons in gauge theories. The relation between the
field theory dyons and those counted by the Igusa cusp form
in toroidally compactified heterotic string is elucidated.Comment: Some typos corrected and references adde
Nernst branes in gauged supergravity
We study static black brane solutions in the context of N = 2 U(1) gauged
supergravity in four dimensions. Using the formalism of first-order flow
equations, we construct novel extremal black brane solutions including examples
of Nernst branes, i.e. extremal black brane solutions with vanishing entropy
density. We also discuss a class of non-extremal generalizations which is
captured by the first-order formalism.Comment: 44 pages, 3 figures, v2: added appendix B and references, minor
typographic changes, v3: added some clarifying remarks, version published in
JHE
Matrix dynamics of fuzzy spheres
We study the dynamics of fuzzy two-spheres in a matrix model which represents
string theory in the presence of RR flux. We analyze the stability of known
static solutions of such a theory which contain commuting matrices and SU(2)
representations. We find that irreducible as well as reducible representations
are stable. Since the latter are of higher energy, this stability poses a
puzzle. We resolve this puzzle by noting that reducible representations have
marginal directions corresponding to non-spherical deformations. We obtain new
static solutions by turning on these marginal deformations. These solutions now
have instability or tachyonic directions. We discuss condensation of these
tachyons which correspond to classical trajectories interpolating from
multiple, small fuzzy spheres to a single, large sphere. We briefly discuss
spatially independent configurations of a D3/D5 system described by the same
matrix model which now possesses a supergravity dual.Comment: 26 pages, 3 figures, uses JHEP.cls; (v2) references adde
Exploring the vicinity of the Bogomol'nyi-Prasad-Sommerfield bound
We investigate systems of real scalar fields in bidimensional spacetime,
dealing with potentials that are small modifications of potentials that admit
supersymmetric extensions. The modifications are controlled by a real
parameter, which allows implementing a perturbation procedure when such
parameter is small. The approach allows obtaining the energy and topological
charge in closed forms, up to first order in the parameter. We illustrate the
procedure with some examples. In particular, we show how to remove the
degeneracy in energy for the one-field and the two-field solutions that appear
in a model of two real scalar fields.Comment: Revtex, 9 pages, To be published in J. Phys.
Nonabelian gauge field and dual description of fuzzy sphere
In matrix models, higher dimensional D-branes are obtained by imposing a
noncommutative relation to coordinates of lower dimensional D-branes. On the
other hand, a dual description of this noncommutative space is provided by
higher dimensional D-branes with gauge fields. Fuzzy spheres can appear as a
configuration of lower dimensional D-branes in a constant R-R field strength
background. In this paper, we consider a dual description of higher dimensional
fuzzy spheres by introducing nonabelian gauge fields on higher dimensional
spherical D-branes. By using the Born-Infeld action, we show that a fuzzy
-sphere and spherical D-branes with a nonabelian gauge field whose
Chern character is nontrivial are the same objects when is large. We
discuss a relationship between the noncommutative geometry and nonabelian gauge
fields. Nonabelian gauge fields are represented by noncommutative matrices
including the coordinate dependence. A similarity to the quantum Hall system is
also studied.Comment: 28 page
BPS black holes in N=2 D=4 gauged supergravities
We construct and analyze BPS black hole solutions in gauged N=2, D=4
supergravity with charged hypermultiplets. A class of solutions can be found
through spontaneous symmetry breaking in vacua that preserve maximal
supersymmetry. The resulting black holes do not carry any hair for the scalars.
We demonstrate this with explicit examples of both asymptotically flat and
anti-de Sitter black holes. Next, we analyze the BPS conditions for
asymptotically flat black holes with scalar hair and spherical or axial
symmetry. We find solutions only in cases when the metric contains ripples and
the vector multiplet scalars become ghost-like. We give explicit examples that
can be analyzed numerically. Finally, we comment on a way to circumvent the
ghost-problem by introducing also fermionic hair.Comment: 40 pages, 2 figures; v2 references added; v3 minor changes, published
versio
Massive Gravity Theories and limits of Ghost-free Bigravity models
We construct a class of theories which extend New Massive Gravity to higher
orders in curvature in any dimension. The lagrangians arise as limits of a new
class of bimetric theories of Lovelock gravity, which are unitary theories free
from the Boulware-Deser ghost. These Lovelock bigravity models represent the
most general non-chiral ghost-free theories of an interacting massless and
massive spin-two field in any dimension. The scaling limit is taken in such a
way that unitarity is explicitly broken, but the Boulware-Deser ghost remains
absent. This automatically implies the existence of a holographic -theorem
for these theories. We also show that the Born-Infeld extension of New Massive
Gravity falls into our class of models demonstrating that this theory is also
free of the Boulware-Deser ghost. These results extend existing connections
between New Massive Gravity, bigravity theories, Galileon theories and
holographic -theorems.Comment: 11+5 page
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