333 research outputs found
On the Stability of a Stringy Black Hole
We study the stability under perturbations of a charged four dimensional
stringy black hole arising from gauging a previously studied WZW model. We find
that the black hole is stable only in the extremal case .Comment: 14 pages + 1 figure (not included but available on request
The vacuum polarization around an axionic stringy black hole
We consider the effect of vacuum polarization around the horizon of a 4
dimensional axionic stringy black hole. In the extreme degenerate limit
(), the lower limit on the black hole mass for avoiding the polarization
of the surrounding medium is ( is the
proton mass), according to the assumed value of the axion mass (). In this case, there are no upper bounds on the mass
due to the absence of the thermal radiation by the black hole. In the
nondegenerate (classically unstable) limit (), the black hole always
polarizes the surrounding vacuum, unless the effective cosmological constant of
the effective stringy action diverges.Comment: 7 pages, phyzzx.tex, ROM2F-92-3
Non-linear WKB Analysis of the String Equation
We apply non-linear WKB analysis to the study of the string equation. Even
though the solutions obtained with this method are not exact, they approximate
extremely well the true solutions, as we explicitly show using numerical
simulations. ``Physical'' solutions are seen to be separatrices corresponding
to degenerate Riemann surfaces. We obtain an analytic approximation in
excellent agreement with the numerical solution found by Parisi et al. for the
case.Comment: 21 pages. To appear in the proceedings of the Research Conference on
Advanced Quantum Field Theory and Critical Phenomena, held in Como (Italy),
June 17-21, 1991 -- World Scientifi
A Conformal Affine Toda Model of 2D Black Holes: A Quantum Study of the Evaporation End-Point
In this paper we reformulate the dilaton-gravity theory of Callan \etal\ as a
new effective conformal field theory which turns out to be a generalization of
the so-called -conformal affine Toda (CAT) theory studied some times ago
by Babelon and Bonora. We quantize this model, thus keeping in account the
dilaton-gravity quantum effects. We then implement a Renormalization Group
analysis to study the black hole thermodynamics and the final state of the
Hawking evaporation.Comment: 15 pages, phyzzx, ROM-2F-92-5
Multi - instantons, supersymmetry and topological field theories
In this letter we argue that instanton-dominated Green's functions in N=2 Super Yang-Mills theories can be equivalently computed either using the so-called constrained instanton method or making reference to the topological twisted version of the theory. Defining an appropriate BRST operator (as a supersymmetry plus a gauge variation), we also show that the expansion coefficients of the Seiberg-Witten effective action for the low-energy degrees of freedom can be written as integrals of total derivatives over the moduli space of self-dual gauge connections
Quantum Models of Black Hole Evaporation
The discovery of black-hole evaporation represented in many respects a
revolutionary event in scientific world; as such, in giving answers to open
questions, it gave rise to new problems part of which are still not resolved.
Here we want to make a brief review of such problems and examine some possible
solutions. Invited Talk at the "Workshop on String Theory, Quantum Gravity and
the Unification of the Fundamental Interactions" Rome, September 21-26Comment: 9 pages, ROM2F-92/6
Dynamical Supersymmetry Breaking in Intersecting Brane Models
In this paper we study dynamical supersymmetry breaking in absence of gravity
with the matter content of the minimal supersymmetric standard model. The
hidden sector of the theory is a strongly coupled gauge theory, realized in
terms of microscopic variables which condensate to form mesons. The
supersymmetry breaking scalar potential combines F, D terms with instanton
generated interactions in the Higgs-mesons sector. We show that for a large
region in parameter space the vacuum breaks in addition to supersymmetry also
electroweak gauge symmetry. We furthermore present local D-brane configurations
that realize these supersymmetry breaking patterns.Comment: 30 pages, 4 figures, pdflate
S-duality and the prepotential in N=2* theories (I): the ADE algebras
The prepotential of N=2* supersymmetric theories with unitary gauge groups in
an Omega-background satisfies a modular anomaly equation that can be
recursively solved order by order in an expansion for small mass. By requiring
that S-duality acts on the prepotential as a Fourier transform we generalise
this result to N=2* theories with gauge algebras of the D and E type and show
that their prepotentials can be written in terms of quasi-modular forms of
SL(2,Z). The results are checked against microscopic multi-instanton calculus
based on localization for the A and D series and reproduce the known
1-instanton prepotential of the pure N=2 theories for any gauge group of ADE
type. Our results can also be used to obtain the multi-instanton terms in the
exceptional theories for which the microscopic instanton calculus and the ADHM
construction are not available.Comment: 33 pages, LaTeX2e, added references, version to be published in JHE
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