# Ashoke Sen's research while affiliated with International Centre for Theoretical Sciences and other places

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## Publications (246)

We compute the normalization of the D-instanton amplitudes in type 0B string theory in two dimensions and find perfect agreement with the dual matrix model result.

A bstract
We use string field theory to fix the normalization of the D-instanton corrections to the superpotential involving the moduli fields of type II string theory compactified on an orientifold of a Calabi-Yau threefold in the absence of fluxes. We focus on O (1) instantons whose only zero modes are the four bosonic modes associated with trans...

A bstract
We use insights from string field theory to analyze and cure the divergences in the cylinder diagram in minimal string theory with both boundaries lying on a ZZ brane. We focus on theories with worldsheet matter consisting of the (2 , p ) minimal model plus Liouville theory, with total central charge 26, together with the usual bc -ghosts...

We compute the normalization of the general multi-instanton contribution to the partition function of $(p',p)$ minimal string theory and also to the dual two-matrix integral. We find perfect agreement between the two results.

We use string field theory to fix the normalization of the D-instanton corrections to the superpotential involving the moduli fields of type II string theory compactified on an orientifold of a Calabi-Yau threefold in the absence of fluxes. We focus on $O(1)$ instantons whose only zero modes are the four bosonic modes associated with translation of...

We use insights from string field theory to analyze and cure the divergences in the cylinder diagram in minimal string theory with both boundaries lying on a ZZ brane. We focus on theories with worldsheet matter consisting of a $(2,p)$ minimal model plus Liouville theory, with total central charge 26. This procedure gives a finite, purely imaginary...

A bstract
Classical soft graviton theorem gives the gravitational wave-form at future null infinity at late retarded time u for a general classical scattering. The large u expansion has three known universal terms: the constant term, the term proportional to 1 /u and the term proportional to ln u/u ² , whose coefficients are determined solely in te...

A bstract
We compute the normalization of the multiple D-instanton amplitudes in type IIB string theory and show that the result agrees with the prediction of S-duality due to Green and Gutperle.

A bstract
We compute the contribution of Euclidean D-branes in type IIB string theory on Calabi-Yau threefolds to the metric on the hypermultiplet moduli space in the large volume, weak coupling limit. Our results are in perfect agreement with the predictions based on S-duality, mirror symmetry and supersymmetry.

A bstract
We compute the normalization of single D-instanton amplitudes in type IIB string theory and show that the result agrees with the prediction of S-duality due to Green and Gutperle.

A bstract
Type IIA string theory compactified on a Calabi-Yau threefold has a hypermultiplet moduli space whose metric is known to receive non-perturbative corrections from Euclidean D2-branes wrapped on 3-cycles. These corrections have been computed earlier by making use of mirror symmetry, S-duality and twistorial description of quaternionic geom...

A bstract
D-instanton amplitudes suffer from various infrared divergences associated with tachyonic or massless open string modes, leading to ambiguous contribution to string amplitudes. It has been shown previously that string field theory can resolve these ambiguities and lead to unambiguous expressions for D-instanton contributions to string amp...

A bstract
In [4] Balthazar, Rodriguez and Yin (BRY) computed the one instanton contribution to the two point scattering amplitude in two dimensional string theory to first subleading order in the string coupling. Their analysis left undetermined two constants due to divergences in the integration over world-sheet variables, but they were fixed by n...

We compute the contribution of Euclidean D-branes in type IIB string theory on Calabi-Yau threefolds to the metric on the hypermultiplet moduli space in the large volume, weak coupling limit. Our results are in perfect agreement with the predictions based on S-duality, mirror symmetry and supersymmetry.

Type IIA string theory compactified on a Calabi-Yau threefold has a hypermultiplet moduli space whose metric is known to receive non-perturbative corrections from Euclidean D2-branes wrapped on 3-cycles. These corrections have been computed earlier by making use of mirror symmetry, S-duality and twistorial description of quaternionic geometries. In...

A bstract
In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the pr...

Classical soft graviton theorem gives the gravitational wave-form at future null infinity at late retarded time $u$ for a general classical scattering. The large $u$ expansion has three known universal terms: the constant term, the term proportional to $1/u$ and the term proportional to $\ln u/u^2$, whose coefficients are determined solely in terms...

Black holes in a class of string compactifications, known as STU models, carry four electric and four magnetic charges. Furthermore, a duality group, given by the product of three congruence subgroups of SL(2,Z\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usep...

A bstract
In a recent paper, Balthazar, Rodriguez and Yin found remarkable agreement between the one instanton contribution to the scattering amplitudes of two dimensional string theory and those in the matrix model to the first subleading order. The comparison was carried out numerically by analytically continuing the external energies to imaginar...

A bstract
D-instanton world-volume theory has open string zero modes describing collective coordinates of the instanton. The usual perturbative amplitudes in the D-instanton background suffer from infra-red divergences due to the presence of these zero modes, and the usual approach of analytic continuation in momenta does not work since all open st...

Black holes in a class of string compactifications, known as STU models, carry four electric and four magnetic charges. Furthermore a duality group, given by the product of three congruence subgroups of $SL(2,\mathbb{Z})$, acts on these integer valued charges. By placing these eight charges at the eight corners of a Bhargava cube, we provide a clas...

Classical subleading soft graviton theorem in four space-time dimensions determines the gravitational wave-form at late and early retarded time, generated during a scattering or explosion, in terms of the four momenta of the ingoing and outgoing objects. This result was ‘derived’ earlier by taking the classical limit of the quantum soft graviton th...

The classical soft graviton theorem gives an expression for the spectrum of low frequency gravitational radiation, emitted during a classical scattering process, in terms of the trajectories and spin angular momenta of ingoing and outgoing objects, including hard radiation. This has been proved to subleading order in the expansion in powers of the...

A bstract
In a recent paper, Balthazar, Rodriguez and Yin found some remarkable agreement between the results of c = 1 matrix model and D-instanton corrections in two dimensional string theory. Their analysis left undetermined two constants in the string theory computation which had to be fixed by comparing the results with the matrix model results...

We construct Lorentz invariant and gauge invariant 1PI effective action for closed and open superstrings and demonstrate that it satisfies the classical BV master equation. We also construct the quantum master action for this theory satisfying the quantum BV master equation and generalize the construction to unoriented theories. The extra free fiel...

Classical subleading soft graviton theorem in four space-time dimensions determines the gravitational wave-form at late and early retarded time, generated during a scattering or explosion, in terms of the four momenta of the ingoing and outgoing objects. This result was `derived' earlier by taking the classical limit of the quantum soft graviton th...

A bstract
Even at tree level, the first quantized string theory suffers from apparent short distance singularities associated with collision of vertex operators that prevent us from straightforward numerical computation of various quantities. Examples include string theory S-matrix for generic external momenta and computation of the spectrum of str...

We construct Lorentz invariant and gauge invariant 1PI effective action for closed and open superstrings and demonstrate that it satisfies the classical BV master equation. We also construct the quantum master action for this theory satisfying the quantum BV master equation and generalize the construction to unoriented theories. The extra free fiel...

We show that the recently discovered logarithmic terms in the soft-graviton theorem induce a late time component in the gravitational waveform that falls off as inverse power of time, producing a tail term to the linear memory effect.

Classical soft graviton theorem gives an expression for the spectrum of low frequency gravitational radiation, emitted during a classical scattering process, in terms of the trajectories and spin angular momenta of ingoing and outgoing objects, including hard radiation. This has been proved to subleading order in the expansion in powers of frequenc...

A bstract
Bros, Epstein and Glaser proved crossing symmetry of the S-matrix of a theory without massless fields by using certain analyticity properties of the off-shell momentum space Green’s function in the complex momentum plane. The latter properties follow from representing the momentum space Green’s function as Fourier transform of the positio...

A bstract
We explore the logarithmic terms in the soft theorem in four dimensions by analyzing classical scattering with generic incoming and outgoing states and one loop quantum scattering amplitudes. The classical and quantum results are consistent with each other. Although most of our analysis in quantum theory is carried out for one loop amplit...

A bstract
The complete proof of cutting rules needed for proving perturbative unitarity of quantum field theories usually employs the largest time equation or old fashioned perturbation theory. None of these can be generalized to string field theory that has non-local vertices. In arXiv:1604.01783 we gave a proof of cutting rules in string field th...

Bros, Epstein and Glaser proved crossing symmetry of the S-matrix of a theory without massless fields by using certain analyticity properties of the off-shell momentum space Green's function in the complex momentum plane. The latter properties follow from representing the momentum space Green's function as Fourier transform of the position space Gr...

A bstract
It has been shown that in larger than four space-time dimensions, soft factors that relate the amplitudes with a soft photon or graviton to amplitudes without the soft particle also determine the low frequency radiative part of the electromagnetic and gravitational fields during classical scattering. In four dimensions the S-matrix become...

Superstring field theory expresses the perturbative S-matrix of superstring theory as a sum of Feynman diagrams each of which is manifestly free from ultraviolet divergences. The interaction vertices fall off exponentially for large space-like external momenta making the ultraviolet finiteness property manifest, but blow up exponentially for large...

We explore the logarithmic terms in the soft theorem in four dimensions by analyzing classical scattering with generic incoming and outgoing states and one loop quantum scattering amplitudes. The classical and quantum results are consistent with each other. Although most of our analysis in quantum theory is carried out for one loop amplitudes in a...

We show that the recently discovered logarithmic terms in the soft graviton theorem induce a late time component in the gravitational wave-form that falls off as inverse power of time, producing a tail term to both the linear and non-linear memory effects. In particular for the case of binary black hole merger the coefficient of this term has simpl...

The complete proof of cutting rules needed for proving perturbative unitarity of quantum field theories usually employs the largest time equation or old fashioned perturbation theory. None of these can be generalized to string field theory that has non-local vertices. In arXiv:1604.01783 we gave a proof of cutting rules in string field theory, whic...

It has been shown that in larger than four space-time dimensions, soft factors that relate the amplitudes with a soft photon or graviton to amplitudes without the soft particle also determine the low frequency radiative part of the electromagnetic and gravitational fields during classical scattering. In four dimensions the S-matrix becomes infrared...

The absence of exotics is a conjectural property of the spectrum of BPS
states of four--dimensional $\mathcal{N}=2$ supersymmetric QFT's. In this
letter we revisit the precise statement of this conjecture, and develop a
general strategy that, if applicable, entails the absence of exotic BPS states.
Our method is based on the Coulomb branch formula...

A bstract
Classical limit of multiple soft graviton theorem can be used to compute the angular power spectrum of long wavelength gravitational radiation in classical scattering provided the total energy carried away by the radiation is small compared to the energies of the scatterers. We could ensure this either by taking the limit in which the imp...

Given a family of world-sheet superconformal field theories related by marginal deformation, we can formulate superstring field theory based on any of these world-sheet theories. Background independence is the statement that these different superstring field theories are related to each other by field redefinition. We prove background independence...

In arXiv:1707.06803 we derived the subleading multiple soft graviton theorem in a generic quantum theory of gravity for arbitrary number of soft external gravitons and arbitrary number of finite energy external states carrying arbitrary mass and spin. In this paper we verify this explicitly using the CHY formula for tree level scattering amplitudes...

We derive the subleading soft graviton theorem in a generic quantum theory of gravity for arbitrary number of soft external gravitons and arbitrary number of finite energy external states carrying arbitrary mass and spin. Our results are valid to all orders in perturbation theory when the number of non-compact space-time dimensions is six or more,...

We analyze scattering amplitudes with one soft external graviton and arbitrary number of other finite energy external states carrying arbitrary mass and spin to sub-subleading order in the momentum of the soft graviton. Our result can be expressed as the sum of a universal part that depends only on the amplitude without the soft graviton and not th...

We review recent developments in the construction of heterotic and type II string field theories and their various applications. These include systematic procedures for determining the shifts in the vacuum expectation values of fields under quantum corrections, computing renormalized masses and S-matrix of the theory around the shifted vacuum and a...

A bstract
Superstring field theory gives expressions for heterotic and type II string loop amplitudes that are free from ultraviolet and infrared divergences when the number of non-compact space-time dimensions is five or more. We prove the subleading soft graviton theorem in these theories to all orders in perturbation theory for S-matrix elements...

We use insights from superstring field theory to prove the subleading soft graviton theorem for tree amplitudes of (compactified) heterotic and type II string theories for arbitrary number of finite energy NS (NSNS) sector states but only one soft graviton. We also prove the leading soft graviton theorem in these theories for arbitrary number of ex...

Conventional superstring perturbation theory based on the world-sheet approach gives divergent results for the S-matrix whenever the total center of mass energy of the incoming particles exceeds the threshold of production of any final state consistent with conservation laws. Two systematic approaches have been suggested for dealing with this diffi...

By integrating out the heavy fields in type II or heterotic string field theory one can construct the effective action for the light fields. This effective theory inherits all the algebraic structures of the parent theory and the effective action automatically satisfies the Batalin-Vilkovisky quantum master equation. This theory is manifestly ultra...

We complete the proof of unitarity of (compactified) heterotic and type II string field theories by showing that in the cut diagrams only physical states appear in the sum over intermediate states. This analysis takes into account the effect of mass and wave-function renormalization, and the possibility that the true vacuum may be related to the pe...

Most of the massive states in superstring theory are expected to undergo mass renormalization at one loop order. Typically these corrections should contain imaginary parts, indicating that the states are unstable against decay into lighter particles. However in such cases, direct computation of the renormalized mass using superstring perturbation t...

We determine the reality conditions on the string fields that make the action for heterotic and type II string field theories real.

Superstring field theory expresses the perturbative S-matrix of superstring theory as a sum of Feynman diagrams each of which is manifestly free from ultraviolet divergences. The interaction vertices fall off exponentially for large space-like external momenta making the ultraviolet finiteness property manifest, but blow up exponentially for large...

Taking clues from the recent construction of the covariant action for type II
and heterotic string field theories, we construct a manifestly Lorentz
covariant action for type IIB supergravity, and discuss its gauge fixing
maintaining manifest Lorentz invariance. The action contains a
(non-gravitating) free 4-form field besides the usual fields of t...

From the analysis of the near horizon geometry and supersymmetry algebra it
has been argued that all the microstates of single centered BPS black holes
with four unbroken supersymmetries carry zero angular momentum in the region of
the moduli space where the black hole description is valid. A stronger form of
the conjecture would be that the result...

We construct the quantum BV master action for heterotic and type II string
field theories.

Superstring perturbation theory based on the 1PI effective theory approach
has been useful for addressing the problem of mass renormalization and vacuum
shift. We derive Ward identities associated with space-time supersymmetry
transformation in this approach. This leads to a proof of the equality of
renormalized masses of bosons and fermions and id...

In a metastable de Sitter space any object has a finite life expectancy
beyond which it undergoes vacuum decay. However, by spreading into different
parts of the universe which will fall out of causal contact of each other in
future, a civilization can increase its collective life expectancy, defined as
the average time after which the last settlem...

The discovery that most of the energy density in the universe is stored in
the form of dark energy has profound consequences for our future. In particular
our current limited understanding of quantum theory of gravity indicates that
some time in the future our universe will undergo a phase transition that will
destroy us and everything else around...

We construct off-shell amplitudes in heterotic and type II string theories
involving arbitrary combination of Ramond and Neveu-Schwarz sector external
states. We also construct the equations of motion of a gauge invariant 1PI
effective field theory which reproduces these off-shell amplitudes. Using this
construction we prove that the renormalized p...

We construct gauge invariant 1PI effective action for the NS sector of type
II and heterotic string field theory. By construction, zero eigenvalues of the
kinetic operator of this action determine the renormalized physical masses, and
tree level amplitudes computed from this action (after gauge fixing) give the
loop corrected S-matrix elements. Usi...

Computing the renormalized masses and S-matrix elements in string theory,
involving states whose masses are not protected from quantum corrections,
requires defining off-shell amplitude with certain factorization properties.
While in the bosonic string theory one can in principle construct such an
amplitude from string field theory, there is no ful...

Exact results for the BPS index are known for a class of BPS dyons in type II
string theory compactified on a six dimensional torus. In this paper we set up
the problem of counting the same BPS states in a duality frame in which the
states carry only Ramond-Ramond charges. We explicitly count the number of
states carrying the lowest possible charge...

In recent series of works, by translating properties of multi-centered
supersymmetric black holes into the language of quiver representations, we
proposed a formula that expresses the Hodge numbers of the moduli space of
semi-stable representations of quivers with generic superpotential in terms of
a set of invariants associated to `single-centered...

In some string theories, e.g. SO(32) heterotic string theory on Calabi-Yau
manifolds, a massless field with a tree level potential can acquire a tachyonic
mass at the one loop level, forcing us to quantize the theory around a new
background that is not a solution to the classical equations of motion and
hence is not described by a conformally invar...

In some string theories, e.g. SO(32) heterotic string theory on Calabi-Yau manifolds, a massless field with a tree level potential can acquire a tachyonic mass at the one loop level, forcing us to quantize the theory around a new background that is not a solution to the classical equations of motion and hence is not described by a conformally invar...

This is a short review summarizing the current status of the comparison
between microscopic and macroscopic entropy of extremal BPS black holes in
string theory.

In a previous paper we described a procedure for computing the renormalized
masses and S-matrix elements in bosonic string theory for a special class of
massive states which do not mix with unphysical states under renormalization.
In this paper we extend this result to general states in bosonic string theory,
and argue that only the squares of reno...

The partition function on the three-sphere of ABJM theory and its
generalizations has, at large N, a universal, subleading logarithmic term.
Inspired by the success of one-loop quantum gravity for computing the
logarithmic corrections to black hole entropy, we try to reproduce this
universal term by a one-loop calculation in Euclidean eleven-dimens...

We study the mass of the stable non-BPS state in type I / heterotic string
theory compactified on a circle with the help of the interpolation formula
between weak and strong coupling results. Comparison between the results at
different orders indicate that this procedure can determine the mass of the
particle to within 10% accuracy over the entire...

Quiver quantum mechanics is invariant under Seiberg duality. A mathematical
consequence is that the cohomology of the Higgs branch moduli space is
invariant under mutations of the quiver. The Coulomb branch formula, on the
other hand, conjecturally expresses the Poincar\'e / Dolbeault polynomial of
the Higgs branch moduli space in terms of certain...

We consider the problem of resumming the perturbative expansions for
anomalous dimensions of low twist, non-BPS operators in four dimensional N=4
supersymmetric Yang-Mills theories. The requirement of S-duality invariance
imposes considerable restrictions on any such resummation. We introduce several
prescriptions that produce interpolating functio...

Strong - weak coupling duality in string theory allows us to compute physical
quantities both at the weak coupling end and at the strong coupling end.
Furthermore perturbative string theory can be used to compute corrections to
the leading order formula at both ends. We explore the possibility of
constructing a smooth interpolating formula that agr...

In previous work we have shown that the equivariant index of multi-centered
N=2 black holes localizes on collinear configurations along a fixed axis. Here
we provide a general algorithm for enumerating such collinear configurations
and computing their contribution to the index. We apply this machinery to the
case of black holes described by quiver...

N=4 supersymmetric string theories contain negative discriminant states whose
numbers are known precisely from microscopic counting formulae. On the
macroscopic side, these results can be reproduced by regarding these states as
multi-centered black hole configurations provided we make certain
identification of apparently distinct multi-centered bla...

Middle cohomology states on the Higgs branch of supersymmetric quiver quantum
mechanics - also known as pure Higgs states - have recently emerged as possible
microscopic candidates for single-centered black hole micro-states, as they
carry zero angular momentum and appear to be robust under wall-crossing. Using
the connection between quiver quantum...

BPS states in
$ \mathcal{N} $
= 4 supersymmetric SU(N ) gauge theories in four dimensions can be represented as planar string networks with ends lying on D3-branes. We introduce several protected indices which capture information on the spectrum and various quantum numbers of these states, give their wall crossing formula and describe how using th...

Euclidean gravity method has been successful in computing logarithmic
corrections to extremal black hole entropy in terms of low energy data, and
gives results in perfect agreement with the microscopic results in string
theory. Motivated by this success we apply Euclidean gravity to compute
logarithmic corrections to the entropy of various non-extr...

We compute the second Seely-DeWitt coefficient of the kinetic operator of the
metric and gauge fields in Einstein-Maxwell theory in an arbitrary background
field configuration. We then use this result to compute the logarithmic
correction to the entropy of an extremal Kerr-Newmann black hole.

The wall crossing formula of Kontsevich and Soibelman gives an implicit
relation between the BPS indices on two sides of the wall of marginal stability
by equating two symplectomorphisms constructed from the indices on two sides of
the wall. The wall crossing formulae of Manschot, Pioline and the author give
two apparently different explicit expres...

We compute logarithmic corrections to the entropy of supersymmetric extremal black holes in
$ \mathcal{N} = {4} $
and
$ \mathcal{N} = {8} $
supersymmetric string theories and find results in perfect agreement with the microscopic results. In particular these logarithmic corrections vanish for quarter BPS black holes in
$ \mathcal{N} = {4} $
s...

We compute logarithmic corrections to the entropy of rotating extremal black
holes using quantum entropy function i.e. Euclidean quantum gravity approach.
Our analysis includes five dimensional supersymmetric BMPV black holes in type
IIB string theory on T^5 and K3 x S^1 as well as in the five dimensional CHL
models, and also non-supersymmetric ext...

Logarithmic corrections to the extremal black hole entropy can be computed
purely in terms of the low energy data -- the spectrum of massless fields and
their interaction. The demand of reproducing these corrections provides a
strong constraint on any microscopic theory of quantum gravity that attempts to
explain the black hole entropy. Using quant...

We compute logarithmic corrections to the entropy of supersymmetric extremal black holes in N = 4 and N = 8 supersymmetric string theories and find results in perfect agreement with the microscopic results. In particular these logarithmic corrections vanish for quarter BPS black holes in N = 4 supersymmetric theories, but has a finite coefficient f...

Single centered BPS black hole solutions exist only when the charge carried by the black hole has positive discriminant. On the other hand the exact dyon spectrum in heterotic string theory compactified on T
6 is known to contain states with negative discriminant. We show that all of these negative discriminant states can be accounted for as two ce...

We propose a formula for computing the (moduli-dependent) contribution of
multi-centered solutions to the total BPS index in terms of the
(moduli-independent) indices associated to single-centered solutions. The main
tool in our analysis is the computation of the refined index Tr(-y)^{2J_3} of
configurational degrees of freedom of multi-centered BP...

Since euclidean global AdS_2 space represented as a strip has two boundaries,
the state / operator correspondence in the dual CFT_1 reduces to the standard
map from the operators acting on a single copy of the Hilbert space to states
in the tensor product of two copies of the Hilbert space. Using this picture we
argue that the corresponding states...

A key question in the study of N=2 supersymmetric string or field theories is
to understand the decay of BPS bound states across walls of marginal stability
in the space of parameters or vacua. By representing the potentially unstable
bound states as multi-centered black hole solutions in N=2 supergravity, we
provide two fully general and explicit...

For BPS black holes with at least four unbroken supercharges, we describe how the macroscopic entropy can be used to compute an appropriate index, which can be then compared with the same index computed in the microscopic description. We obtain exact results incorporating all higher order quantum corrections in the limit when only one of the charge...

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 i...

We survey recent results on the exact dyon spectrum in a class of N = 4 supersymmetric string theories, and discuss how the results can be understood from the macroscopic viewpoint using AdS(2)/CFT1 correspondence. The comparison between the microscopic and the macroscopic results includes power suppressed corrections to the entropy, the sign of th...

We evaluate the one loop determinant of matter multiplet fields of N=4
supergravity in the near horizon geometry of quarter BPS black holes, and use
it to calculate logarithmic corrections to the entropy of these black holes
using the quantum entropy function formalism. We show that even though
individual fields give non-vanishing logarithmic contr...

AdS
2/CFT
1 correspondence predicts that the logarithm of a \( {\mathbb{Z}_N} \) twisted index over states carrying a fixed set of charges grows as 1/N times the entropy of the black hole carrying the same set of charges. In this paper we verify this explicitly by calculating the microscopic \( {\mathbb{Z}_N} \) twisted index for a class of states...

The microscopic formula for the degeneracies of 1/8 BPS black holes in type II string theory compactified on a six dimensional torus can be expressed as a sum of several terms. One of the terms is a function of the Cremmer-Julia invariant and gives the leading contribution to the entropy in the large charge limit. The other terms, which give expone...

In four dimensional string theories with \( \mathcal{N} = 4 \) and \( \mathcal{N} = 8 \) supersymmetries one can often define twisted index in a subspace of the moduli space which captures additional information on the partition function than the ones contained in the usual helicity trace index. We compute several such indices in type IIB string th...

We review and extend recent attempts to find a precise relation between extremal black hole entropy and degeneracy of microstates using AdS 2 /CFT 1 correspondence. Our analysis leads to a specific relation between degeneracy of black hole microstates and an appropriately defined partition function of string theory on the near horizon geometry - na...

A two charge system in string theory preserving eight supercharges can be described as a small black hole that has zero entropy in the supergravity approximation, but classical higher derivative corrections produce a finite entropy in accordance with the prediction of microstate counting. On the other hand for the same system one can construct smoo...

BMPV black holes in flat transverse space and in Taub-NUT space have identical near horizon geometries but different microscopic degeneracies. It has been proposed that this difference can be accounted for by different contribution to the degeneracies of these black holes from hair modes, -- degrees of freedom living outside the horizon. In this pa...

## Citations

... Over the years, we have understood many issues regarding the non-perturbative landscape of SFT classical solutions and the explicit constructions of complete RNS actions [22][23][24][25][26][27][28]. More recently SFT methods have been used to address non-perturbative Dinstantons corrections to closed string scattering amplitudes [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], which also provided a first-principle resolution of several world-sheet drawbacks associated with degenerations of Riemann surfaces. See [45][46][47] for recent reviews on SFT. ...

... Focusing on the u-behavior associated to the Fourier transform of the terms in the expansion (3.5) [38,40,67] we see that the tree level computations give ...

... In recent years string field theory has proved to be a useful tool in dealing with infrared divergences in the open string theory on the D-instanton, including in the annulus zero point function -see e.g. [5][6][7]. In this paper we use the same approach and get a finite result for the constant N D . ...

... Over the years, we have understood many issues regarding the non-perturbative landscape of SFT classical solutions and the explicit constructions of complete RNS actions [22][23][24][25][26][27][28]. More recently SFT methods have been used to address non-perturbative Dinstantons corrections to closed string scattering amplitudes [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], which also provided a first-principle resolution of several world-sheet drawbacks associated with degenerations of Riemann surfaces. See [45][46][47] for recent reviews on SFT. ...

... Over the years, we have understood many issues regarding the non-perturbative landscape of SFT classical solutions and the explicit constructions of complete RNS actions [22][23][24][25][26][27][28]. More recently SFT methods have been used to address non-perturbative Dinstantons corrections to closed string scattering amplitudes [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], which also provided a first-principle resolution of several world-sheet drawbacks associated with degenerations of Riemann surfaces. See [45][46][47] for recent reviews on SFT. ...