Publications (263)
BPS States on a Three Brane Probe
Ashoke Sen
Recently Banks, Douglas and Seiberg have shown that the world volume theory of a three brane of the type IIB theory in the presence of a configuration of four Dirichlet seven brane…
Infrared finite semi-inclusive cross section in two dimensional type 0B string theory
Ashoke Sen
D-instanton induced S-matrix in type 0B string theory in two dimensions suffers from infrared divergences. This can be traced to the fact that these processes produce low energy ro…
Gauge Invariant 1PI Effective Superstring Field Theory: Inclusion of the Ramond Sector
Ashoke Sen
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…
A Note on Enhanced Gauge Symmetries in M- and String Theory
Ashoke Sen
Two different mechanisms exist in non-perturbative String / M- theory for enhanced SU(N) (SO(2N)) gauge symmetries. It can appear in type IIA string theory or M-theory near an $A_{…
Mock Modularity In CHL Models
Ajit Bhand, Ashoke Sen, Ranveer Kumar Singh
Dabholkar, Murthy and Zagier (DMZ) proved that there is a canonical decomposition of a meromorphic Jacobi form of integral index for with poles on tors…
Orientifold Limit of F-theory Vacua
Ashoke Sen
We show how F-theory on a Calabi-Yau (n+1)-fold, in appropriate limit, can be identified as an orientifold of type IIB string theory compactified on a Calabi-Yau n-fold.
Dynamics of Multiple Kaluza-Klein Monopoles in M- and String Theory
Ashoke Sen
We analyse the world-volume theory of multiple Kaluza-Klein monopoles in string and M-theory by identifying the appropriate zero modes of various fields. The results are consistent…
Classical Soft Graviton Theorem Rewritten
Biswajit Sahoo, Ashoke Sen
Classical soft graviton theorem gives the gravitational wave-form at future null infinity at late retarded time for a general classical scattering. The large expansion has…
Logarithm of charge ratio in black hole entropy
Muktajyoti Saha, Ashoke Sen, P. Shanmugapriya
Logarithmic correction to BPS black hole entropy, computed from microscopic description, often contains terms involving large ratios of charges, besides the logarithmic terms invol…
Are Moduli Vacuum Expectation Values or Parameters?
Ashoke Sen
Banks has argued that the moduli of string theory are not vacuum expectation values but parameters. We offer a different perspective on this question. Given two different points P…
About the Absence of Exotics and the Coulomb Branch Formula
Michele Del Zotto, Ashoke Sen
The absence of exotics is a conjectural property of the spectrum of BPS states of four--dimensional supersymmetric QFT's. In this letter we revisit the precise stat…
Large Marginal Deformations in String Field Theory
Ashoke Sen, Barton Zwiebach
We use the level truncation scheme to obtain accurate descriptions of open bosonic string field configurations corresponding to large marginal deformations such as background Wilso…
Spinning Strings as Small Black Rings
Atish Dabholkar, Norihiro Iizuka, Ashik Iqubal +2
Certain supersymmetric elementary string states with spin can be viewed as small black rings whose horizon has the topology of S^1 \times S^{d-3} in a d-dimensional string theory.…
Supersymmetric Index from Black Hole Entropy
Atish Dabholkar, Joao Gomes, Sameer Murthy +1
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 t…
Do All BPS Black Hole Microstates Carry Zero Angular Momentum?
Abhishek Chowdhury, Richard S. Garavuso, Swapnamay Mondal +1
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 supersymm…
On the Background Independence of String Field Theory: III. Explicit Field Redefinitions
Ashoke Sen
Given two conformal field theories related to each other by a marginal perturbation, and string field theories constructed around such backgrounds, we show how to construct explici…
Strong Coupling Dynamics of Branes from M-theory
Ashoke Sen
We study some aspects of the strong coupling dynamics of Dirichlet six branes, anti- six branes, and orientifold planes by using the equivalence of type IIA string theory and M-the…
A Note on Gauge Transformations in Batalin-Vilkovisky Theory
Ashoke Sen, Barton Zwiebach
We give a generally covariant description, in the sense of symplectic geometry, of gauge transformations in Batalin-Vilkovisky quantization. Gauge transformations exist not only at…
Uniqueness of Tachyonic Solitons
Ashoke Sen
It has been conjectured that condensation of tachyons on a bosonic D-brane gives rise to vacuum / soliton solutions which are independent of the initial magnetic field on the D-bra…
Off-shell Amplitudes in Superstring Theory
Ashoke Sen
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 ampl…
Covariant Action for Type IIB Supergravity
Ashoke Sen
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 s…
Star Algebra Spectroscopy
Leonardo Rastelli, Ashoke Sen, Barton Zwiebach
The spectrum of the infinite dimensional Neumann matrices M^{11}, M^{12} and M^{21} in the oscillator construction of the three-string vertex determines key properties of the star…
Stable Non-BPS Bound States of BPS D-branes
Ashoke Sen
S-duality symmetry of type IIB string theory predicts the existence of a stable non-BPS state on an orbifold five plane of the type IIB theory if the orbifold group is generated by…
Strong-Weak Coupling Duality in Three Dimensional String Theory
Ashoke Sen
Following an old result of Marcus and Schwarz we argue that in the heterotic string theory compactified on a seven dimensional torus, the target space duality group O(7,23;Z) and t…
Kaluza-Klein Dyons in String Theory
Ashoke Sen
S-duality of hetertotic / type II string theory compactified on a six dimensional torus requires the existence of Kaluza-Klein dyons, carrying winding charge. We identify the zero…
Field Theory of Tachyon Matter
Ashoke Sen
We propose a field theory for describing the tachyon on a brane-antibrane system near the minimum of the potential. This field theory realizes two known properties of the tachyon e…
Classical Solutions in String Field Theory Around the Tachyon Vacuum
Leonardo Rastelli, Ashoke Sen, Barton Zwiebach
In a previous paper [hep-th/0012251] we proposed a simple class of actions for string field theory around the tachyon vacuum. In this paper we search for classical solutions descri…
Star Algebra Projectors
Davide Gaiotto, Leonardo Rastelli, Ashoke Sen +1
Surface states are open string field configurations which arise from Riemann surfaces with a boundary and form a subalgebra of the star algebra. We find that a general class of sta…
Linear b-Gauges for Open String Fields
Michael Kiermaier, Ashoke Sen, Barton Zwiebach
Motivated by Schnabl's gauge choice, we explore open string perturbation theory in gauges where a linear combination of antighost oscillators annihilates the string field. We find…
Duality Symmetric Actions
John H. Schwarz, Ashoke Sen
It is frequently useful to construct dual descriptions of theories containing antisymmetric tensor fields by introducing a new potential whose curl gives the dual field strength, t…
Black Hole Bound State Metamorphosis
Abhishek Chowdhury, Shailesh Lal, Arunabha Saha +1
N=4 supersymmetric string theories contain negative discriminant states whose numbers are known precisely from microscopic counting formulae. On the macroscopic side, these results…
Energy Momentum Tensor and Marginal Deformations in Open String Field Theory
Ashoke Sen
Marginal boundary deformations in a two dimensional conformal field theory correspond to a family of classical solutions of the equations of motion of open string field theory. In…
U-duality and Intersecting D-branes
Ashoke Sen
Spectrum of elementary string states in type II string theory compactified on a torus contains short multiplets which are invariant under only one quarter of the space-time supersy…
Supersymmetry Restoration in Superstring Perturbation Theory
Ashoke Sen
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 ident…
S-duality Improved Perturbation Theory in Compactified Type I / Heterotic String Theory
Roji Pius, Ashoke Sen
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 coupli…
Duality Orbits, Dyon Spectrum and Gauge Theory Limit of Heterotic String Theory on T^6
Shamik Banerjee, Ashoke Sen
For heterotic string theory compactified on T^6, we derive the complete set of T-duality invariants which characterize a pair of charge vectors (Q,P) labelling the electric and mag…
An Introduction to Non-perturbative String Theory
Ashoke Sen
In this review I discuss some basic aspects of non-perturbative string theory. The topics include test of duality symmetries based on the analysis of the low energy effective actio…
Non-supersymmetric D-Brane Configurations with Bose-Fermi Degenerate Open String Spectrum
Matthias R Gaberdiel, Ashoke Sen
The spectrum of open strings on various non-BPS D-brane configurations in type II string theory on a K3 orbifold is analysed. At a generic point in the corresponding moduli space t…
Black Hole Hair Removal: Non-linear Analysis
Dileep P. Jatkar, Ashoke Sen, Yogesh K. Srivastava
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 differ…
One Loop Mass Renormalization of Unstable Particles in Superstring Theory
Ashoke Sen
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, indicat…
Macroscopic Charged Heterotic String
Ashoke Sen
Classical solutions of equations of motion in low energy effective field theory, describing fundamental charged heterotic string, are found. These solutions automatically carry an…
Ultraviolet and Infrared Divergences in Superstring Theory
Ashoke Sen
Superstring theory is known to be free from ultraviolet divergences but suffers from the usual infrared divergences that occur in quantum field theories. After briefly reviewing th…
Adding Charges to N=4 Dyons
Nabamita Banerjee, Dileep P. Jatkar, Ashoke Sen
The spectrum of dyons in a class of N=4 supersymmetric string theories has been found for a specific set of electric and magnetic charge vectors. We extend the analysis to more gen…
Orbifolds of M-Theory and String Theory
Ashoke Sen
It is shown that many of the conjectured dualities involving orbifold compactification of M-theory follow from the known dualities involving M-theory and string theory in ten dimen…
Remarks on Tachyon Driven Cosmology
Ashoke Sen
We begin by reviewing the results on the decay of unstable D-branes in type II string theory, and the open-closed string duality proposal that arises from these studies. We then ap…
Duality Symmetries of 4D Heterotic Strings
John H. Schwarz, Ashoke Sen
Target space duality (T duality), which interchanges Kaluza--Klein and winding-mode excitations of the compactified heterotic string, is realized as a symmetry of a world-sheet act…
Time Evolution in Open String Theory
Ashoke Sen
We discuss a general iterative procedure for constructing time dependent solutions in open string theory describing rolling of a generic tachyon field away from its maximum. These…
Heterotic Effective Action and Duality Symmetries Revisited
Olaf Hohm, Ashoke Sen, Barton Zwiebach
The dimensional reduction of heterotic supergravity with gauge fields truncated to the Cartan subalgebra exhibits a continuous O(d,d+16;R) global symmetry, related to the O(d,d+16;…
Wall-Crossing from Boltzmann Black Hole Halos
Jan Manschot, Boris Pioline, Ashoke Sen
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 paramet…
Generalities of Quarter BPS Dyon Partition Function and Dyons of Torsion Two
Shamik Banerjee, Ashoke Sen, Yogesh K. Srivastava
We propose a general set of constraints on the partition function of quarter BPS dyons in any N=4 supersymmetric string theory by drawing insight from known examples, and study the…
Mass Renormalization in String Theory: Special States
Roji Pius, Arnab Rudra, Ashoke Sen
String theory gives a well defined procedure for computing the S-matrix of BPS or a class of massless states, but similar calculation for general massive states is plagued with dif…
BPS Spectrum, Indices and Wall Crossing in N=4 Supersymmetric Yang-Mills Theories
Ashoke Sen
BPS states in 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 i…
Product Representation of Dyon Partition Function in CHL Models
Justin R. David, Dileep P. Jatkar, Ashoke Sen
A formula for the exact partition function of 1/4 BPS dyons in a class of CHL models has been proposed earlier. The formula involves inverse of Siegel modular forms of subgroups of…
SO(32) Spinors of Type I and Other Solitons on Brane-Antibrane Pair
Ashoke Sen
We construct the SO(32) spinor state in weakly coupled type I string theory as a kink solution of the tachyon field on the D-string - anti-D-string pair and calculate its mass. We…
Subleading Soft Graviton Theorem for Loop Amplitudes
Ashoke Sen
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 s…
Exotic Branes and Symmetries of String Theory
Ashoke Sen
Are duality transformations symmetries of string theory? For AdS space-time the answer is no for generic asymptotic values of the moduli, since the duality symmetry is broken expli…
F-theory and the Gimon-Polchinski Orientifold
Ashoke Sen
We establish the equivalence of the Gimon-Polchinski orientifold and F-theory on an elliptically fibered Calabi-Yau three fold on base by comparing the gauge sym…
Rotating Charged Black Hole Solution in Heterotic String Theory
Ashoke Sen
We construct a solution of the classical equations of motion arising in the low energy effective field theory for heterotic string theory. This solution describes a black hole in f…
Fundamental Strings in Open String Theory at the Tachyonic Vacuum
Ashoke Sen
We show that the world-volume theory on a D-p-brane at the tachyonic vacuum has solitonic string solutions whose dynamics is governed by the Nambu-Goto action of a string moving in…
Dirac-Born-Infeld Action on the Tachyon Kink and Vortex
Ashoke Sen
The tachyon effective field theory describing the dynamics of a non-BPS D-brane in superstring theory has an infinitely thin but finite tension kink solution describing a codimensi…
Duality and Orbifolds
Ashoke Sen
We construct several examples where duality transformation commutes with the orbifolding procedure even when the orbifolding group does not act freely, and there are massless state…
STRING STRING DUALITY CONJECTURE IN SIX DIMENSIONS AND CHARGED SOLITONIC STRINGS
Ashoke Sen
It has recently been conjectured that the type IIA string theory compactified on K3 and the heterotic string theory compactified on a four dimensional torus describe identical stri…
Black Holes and Solitons in String Theory
Ashoke Sen
In this review, I discuss a general method for constructing classical solutions of the equations of motion arising in the effective low energy string theory, and discuss specific a…
Some Applications of String Field Theory
Ashoke Sen
We study general properties of the classical solutions in non-polynomial closed string field theory and their relationship with two dimensional conformal field theories. In particu…
Euclidean D-branes in Type IIB string theory on Calabi-Yau threefolds
Sergei Alexandrov, Ashoke Sen, Bogdan StefaÅski
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 coup…
Cutkosky Rules and Unitarity (Violation) in D-instanton Amplitudes
Ashoke Sen
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 di…
Equivalence of Two Contour Prescriptions in Superstring Perturbation Theory
Ashoke Sen
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 par…
Electric Magnetic Duality in String Theory
Ashoke Sen
The electric-magnetic duality transformation in four dimensional heterotic string theory discussed by Shapere, Trivedi and Wilczek is shown to be an exact symmetry of the equations…
Resummation and S-duality in N=4 SYM
Christopher Beem, Leonardo Rastelli, Ashoke Sen +1
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…
Equivalence of Three Wall Crossing Formulae
Ashoke Sen
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 symplectomor…
Normalization of Type IIB D-instanton Amplitudes
Ashoke Sen
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.
M-Theory on (K3 X S^1)/Z_2
Ashoke Sen
We analyze -theory compactified on where the changes the sign of the three form gauge field, acts on as a parity transformation and on K3 as an…
Black Hole Solutions in Heterotic String Theory on a Torus
Ashoke Sen
We construct the general electrically charged, rotating black hole solution in the heterotic string theory compactified on a six dimensional torus and study its classical propertie…
How Do Black Holes Predict the Sign of the Fourier Coefficients of Siegel Modular Forms?
Ashoke Sen
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 helicit…
Logarithmic Corrections to Schwarzschild and Other Non-extremal Black Hole Entropy in Different Dimensions
Ashoke Sen
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…
Mass Renormalization in String Theory: General States
Roji Pius, Arnab Rudra, Ashoke Sen
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…
Dyon Spectrum in CHL Models
Dileep P. Jatkar, Ashoke Sen
We propose a formula for the degeneracy of quarter BPS dyons in a class of CHL models. The formula uses a modular form of a subgroup of the genus two modular group Sp(2,Z). Our pro…
Strong-Weak Coupling Duality in Four Dimensional String Theory
Ashoke Sen
We present several pieces of evidence for strong-weak coupling duality symmetry in the heterotic string theory, compactified on a six dimensional torus. These include symmetry of t…
How to Create a Flat Ten or Eleven Dimensional Space-time in the Interior of an Asymptotically Flat Four Dimensional String Theory
Ashoke Sen
By taking large mass and charge limit of a black hole in string theory we can create arbitrarily large regions where the space-time is approximately flat, but the moduli fields tak…
How to Expose a Black Hole
Ashoke Sen
According to the correspondence principle of Horowitz and Polchinski, many black holes in string theory are continuously deformed to usual quantum systems involving D-branes and fu…
Descent Relations Among Bosonic D-branes
Ashoke Sen
We show that the tachyonic kink solution on a pair of D-p-branes in the bosonic string theory can be identified with the D-(p-1)-brane of the same theory. We also speculate on the…
Logarithmic Correction to BPS Black Hole Entropy from Supersymmetric Index at Finite Temperature
Anupam A. H., P. V. Athira, Chandramouli Chowdhury +1
It has been argued by Iliesiu, Kologlu and Turiaci in arXiv:2107.09062 that one can compute the supersymmetric index of black holes using black hole geometry carrying finite temper…
Gravitational Wave Tails from Soft Theorem: A Short Review
Ashoke Sen
If a set of massive objects collide in space and the fragments disperse, possibly forming black holes, then this process will emit gravitational waves. Computing the detailed gravi…
Normalization of the Background Independent Open String Field Theory Action
Debashis Ghoshal, Ashoke Sen
It has been shown recently that the background independent open string field theory provides an exact description of the tachyon condensation on unstable D-branes of bosonic string…
Decorating Asymptotically Flat Space-Time with the Moduli Space of String Theory
Ashoke Sen
N=2, 4 and 8 supersymmetric string theories in four dimensional flat space-time have moduli space of vacua. We argue that starting from a theory where the moduli approach a particu…
Black holes and Elementary String States in N=2 Supersymmetric String Theories
Ashoke Sen
We compare the logarithm of the degeneracy of BPS saturated elementary string states and the string modified Bekenstein-Hawking entropy of the corresponding black holes in N=2 supe…
Tachyon Condensation on the Brane Antibrane System
Ashoke Sen
A coincident D-brane - anti-D-brane pair has a tachyonic mode. We present an argument showing that at the classical minimum of the tachyonic potential the negative energy density a…
Higher Derivative Corrections to Non-supersymmetric Extremal Black Holes in N=2 Supergravity
Bindusar Sahoo, Ashoke Sen
Using the entropy function formalism we compute the entropy of extremal supersymmetric and non-supersymmetric black holes in N=2 supergravity theories in four dimensions with highe…
BV Master Action for Heterotic and Type II String Field Theories
Ashoke Sen
We construct the quantum BV master action for heterotic and type II string field theories.
Dyon Spectrum in N=4 Supersymmetric Type II String Theories
Justin R. David, Dileep P. Jatkar, Ashoke Sen
We compute the spectrum of quarter BPS dyons in freely acting Z_2 and Z_3 orbifolds of type II string theory compactified on a six dimensional torus. For large charges the result f…
Divergent to Complex Amplitudes in Two Dimensional String Theory
Ashoke Sen
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…
EXTREMAL BLACK HOLES AND ELEMENTARY STRING STATES
Ashoke Sen
Some of the extremal black hole solutions in string theory have the same quantum numbers as the Bogomol'nyi saturated elementary string states. We explore the possibility that thes…
How Does a Fundamental String Stretch its Horizon?
Ashoke Sen
It has recently been shown that if we take into account a class of higher derivative corrections to the effective action of heterotic string theory, the entropy of the black hole s…
Tachyon Condensation on Separated Brane-Antibrane System
Arjun Bagchi, Ashoke Sen
We study the effect of tachyon condensation on a brane antibrane pair in superstring theory separated in the transverse direction. The static properties of the tachyon potential an…
Black Holes, Elementary Strings and Holomorphic Anomaly
Ashoke Sen
In a previous paper we had proposed a specific route to relating the entropy of two charge black holes to the degeneracy of elementary string states in N=4 supersymmetric heterotic…
All Order Classical Electromagnetic Soft Theorems
Debanjan Karan, Babli Khatun, Biswajit Sahoo +1
If a set of charged objects collide in space and the fragments disperse, then this process will emit electromagnetic waves. Classical soft photon theorem determines the constant te…
Riding Gravity Away from Doomsday
Ashoke Sen
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 under…
Type IIA Dual of the Six-Dimensional CHL Compactification
John H. Schwarz, Ashoke Sen
We propose a candidate for the dual (in the weak/strong coupling sense) of the six-dimensional heterotic string compactification constructed recently by Chaudhuri, Hockney and Lykk…
Quantum Entropy Function from AdS(2)/CFT(1) Correspondence
Ashoke Sen
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 lea…
Generating Function of Single Centered Black Hole Index from the Igusa Cusp Form
Ajit Bhand, Ashoke Sen, Ranveer Kumar Singh
We introduce manifestly duality invariant generating function of the index of single centered black holes in the heterotic string theory compactified on a six dimensional torus. Th…