138 research outputs found
Asymptotic degeneracy of dyonic N=4 string states and black hole entropy
It is shown that the asymptotic growth of the microscopic degeneracy of BPS
dyons in four-dimensional N=4 string theory captures the known corrections to
the macroscopic entropy of four-dimensional extremal black holes. These
corrections are subleading in the limit of large charges and originate both
from the presence of interactions in the effective action quadratic in the
Riemann tensor and from non-holomorphic terms. The presence of the
non-holomorphic corrections and their contribution to the thermodynamic free
energy is discussed. It is pointed out that the expression for the microscopic
entropy, written as a function of the dilaton field, is stationary at the
horizon by virtue of the attractor equations.Comment: 16 pages Late
CHL Dyons and Statistical Entropy Function from D1-D5 System
We give a proof of the recently proposed formula for the dyon spectrum in CHL
string theories by mapping it to a configuration of D1 and D5-branes and
Kaluza-Klein monopole. We also give a prescription for computing the degeneracy
as a systematic expansion in inverse powers of charges. The computation can be
formulated as a problem of extremizing a duality invariant statistical entropy
function whose value at the extremum gives the logarithm of the degeneracy.
During this analysis we also determine the locations of the zeroes and poles of
the Siegel modular forms whose inverse give the dyon partition function in the
CHL models.Comment: LaTeX file, 48 pages; v2: typos correcte
Fundamental Strings and Black Holes
We propose a black hole thermodynamic description of highly excited charged
and uncharged perturbative string states in 3+1 dimensional type II and 4+1
dimensional heterotic string theory. We also discuss the generalization to
extremal and non-extremal black holes carrying magnetic charges.Comment: 25 pages, harvmac; V2: Added reference
A Wave-function for Stringy Universes
We define a wave-function for string theory cosmological backgrounds. We give
a prescription for computing its norm following an earlier analysis within
general relativity. Under Euclidean continuation, the cosmologies we discuss in
this paper are described in terms of compact parafermionic worldsheet systems.
To define the wave-function we provide a T-fold description of the
parafermionic conformal field theory, and of the corresponding string
cosmology. In specific examples, we compute the norm of the wave-function and
comment on its behavior as a function of moduli.Comment: 30 pages, 3 figures, v3: references adde
A Farey tale for N=4 dyons
We study exponentially suppressed contributions to the degeneracies of
extremal black holes. Within Sen's quantum entropy function framework and
focusing on extremal black holes with an intermediate AdS3 region, we identify
an infinite family of semi-classical AdS2 geometries which can contribute
effects of order exp(S_0/c), where S_0 is the Bekenstein-Hawking-Wald entropy
and c is an integer greater than one. These solutions lift to the extremal
limit of the SL(2,Z) family of BTZ black holes familiar from the "black hole
Farey tail". We test this understanding in N=4 string vacua, where exact dyon
degeneracies are known to be given by Fourier coefficients of Siegel modular
forms. We relate the sum over poles in the Siegel upper half plane to the Farey
tail expansion, and derive a "Farey tale" expansion for the dyon partition
function. Mathematically, this provides a (formal) lift from Hilbert modular
forms to Siegel modular forms with a pole at the diagonal divisor.Comment: 31 page
How Do Black Holes Predict the Sign of the Fourier Coefficients of Siegel Modular Forms?
Single centered supersymmetric black holes in four dimensions have
spherically symmetric horizon and hence carry zero angular momentum. This leads
to a specific sign of the helicity trace index associated with these black
holes. Since the latter are given by the Fourier expansion coefficients of
appropriate meromorphic modular forms of Sp(2,Z) or its subgroup, we are led to
a specific prediction for the signs of a subset of these Fourier coefficients
which represent contributions from single centered black holes only. We
explicitly test these predictions for the modular forms which compute the index
of quarter BPS black holes in heterotic string theory on T^6, as well as in Z_N
CHL models for N=2,3,5,7.Comment: LaTeX file, 17 pages, 1 figur
Black Holes in Higher-Dimensional Gravity
These lectures review some of the recent progress in uncovering the phase
structure of black hole solutions in higher-dimensional vacuum Einstein
gravity. The two classes on which we focus are Kaluza-Klein black holes, i.e.
static solutions with an event horizon in asymptotically flat spaces with
compact directions, and stationary solutions with an event horizon in
asymptotically flat space. Highlights include the recently constructed
multi-black hole configurations on the cylinder and thin rotating black rings
in dimensions higher than five. The phase diagram that is emerging for each of
the two classes will be discussed, including an intriguing connection that
relates the phase structure of Kaluza-Klein black holes with that of
asymptotically flat rotating black holes.Comment: latex, 49 pages, 5 figures. Lectures to appear in the proceedings of
the Fourth Aegean Summer School, Mytiline, Lesvos, Greece, September 17-22,
200
4-D gauged supergravity analysis of Type IIB vacua on
We analyze vacua of type IIB string theory on in
presence of three-form fluxes from a four dimensional supergravity viewpoint.
The quaternionic geometry of the moduli space together with the special
geometry of the NS and R-R dilatons and of the -complex structure moduli
play a crucial role in the analysis. The introduction of fluxes corresponds to
a particular gauging of N=2, D=4 supergravity. Our results agree with a recent
work of Tripathy and Trivedi. The present formulation shows the power of
supergravity in the study of effective theories with broken supersymmetry.Comment: AMS-LaTeX, 29 page
Black Holes at the LHC
In these two lectures, we will address the topic of the creation of small
black holes during particle collisions in a ground-based accelerator, such as
LHC, in the context of a higher-dimensional theory. We will cover the main
assumptions, criteria and estimates for their creation, and we will discuss
their properties after their formation. The most important observable effect
associated with their creation is likely to be the emission of Hawking
radiation during their evaporation process. After presenting the mathematical
formalism for its study, we will review the current results for the emission of
particles both on the brane and in the bulk. We will finish with a discussion
of the methodology that will be used to study these spectra, and the observable
signatures that will help us identify the black-hole events.Comment: 37 pages, 14 figures, lectures presented in the 4th Aegean Summer
School on Black Holes, 17-22 September 2007, Lesvos, Greece, typos corrected,
comments and references adde
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