arXiv subjects

Ashoke Sen

Publications and source records attributed to Ashoke Sen.

At least 145 records · Page 8Linked to original sources

arXiv2008

Entropy Function and AdS(2)/CFT(1) Correspondence

Wald's formula for black hole entropy, applied to extremal black holes, leads to the entropy function formalism. We manipulate the entropy computed this way to express it as the logarithm of the ground state degeneracy of a dual quantum mechanical system. This provides a natural definition of the extremal black hole entropy in the full quantum theory. Our analysis also clarifies the relationship between the entropy function formalism and the Euclidean action formalism.

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arXiv2008

Genus Two Surface and Quarter BPS Dyons: The Contour Prescription

Following the suggestion of hep-th/0506249 and hep-th/0612011, we represent quarter BPS dyons in N=4 supersymmetric string theories as string network configuration and explore the role of genus two surfaces in determining the spectrum of such dyons. Our analysis leads to the correct contour prescription for integrating the partition function to determine the spectrum in different domains of the moduli space separated by the walls of marginal stability.

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arXiv2008

Coulomb Branch of the Lorentzian Three Algebra Theory

We analyze the coulomb branch of the non-unitary Lorentzian three algebra theory that has been proposed as a possible candidate for describing the world volume theory of multiple M2-branes. In order that it describes the theory of multiple M2-branes in flat eleven dimensional space-time, the ghost fields must decouple and the physical theory must be independent of the eight coordinates of the moduli space representing the center of mass coordinates of the branes. We show that the structure of the Coulomb branch is consistent with this requirement. While the full moduli space has the structure of a Lorentzian space modded out by a Lorentz transformation, the physical subspace has the correct structure of the moduli space of multiple M2-branes. We also suggest a systematic procedure for testing the consistency of the theory by computing the higher derivative corrections to the effective action obtained by integrating out the massive modes propagating in the loop.

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arXiv2008

Interpreting the M2-brane Action

The world-volume theory of multiple M2-branes proposed recently has a free scalar field. For large vev of this scalar field the world-volume action reduces to that of multiple D2-branes with Yang-Mills coupling proportional to the vev. We suggest that the correct interpretation of this scalar field is as the radial position of the M2-brane center of mass in a cylindrical polar coordinate system. Regarding the azimuthal angle as compact we can regard this as a set of coincident D2-branes in type IIA string theory with varying dilaton and metric. We find that the effective world-volume theory on the D2-branes has Yang-Mills coupling proportional to the radial coordinate; furthermore the radial coordinate satisfies free field equations of motion. This agrees with the corresponding results derived from the M2-brane world-volume theory.

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arXiv2008

Wall Crossing Formula for N=4 Dyons: A Macroscopic Derivation

We derive the wall crossing formula for the decay of a quarter BPS dyon into a pair of half-BPS dyons by analyzing the quantum dynamics of multi-centered black holes in N=4 supersymmetric string theories. Our analysis encompasses the cases where the final decay products are non-primitive dyons. The results are in agreement with the microscopic formula for the dyon spectrum in the special case of heterotic string theory on T^6.

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arXiv2008

Partition Functions of Torsion >1 Dyons in Heterotic String Theory on T^6

The original proposal of Dijkgraaf, Verlinde and Verlinde for the quarter BPS dyon partition function in heterotic string theory on T^6 is known to correctly produce the degeneracy of dyons of torsion 1, i.e. dyons for which gcd(Q\wedge P)=1. We propose a generalization of this formula for dyons of arbitrary torsion. Our proposal satisfies the constraints coming from S-duality invariance, wall crossing formula, black hole entropy and the gauge theory limit. Furthermore using our proposal we derive a general wall crossing formula that is valid even when both the decay products are non-primitive half-BPS dyons.

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arXiv2008

Generalities of Quarter BPS Dyon Partition Function and Dyons of Torsion Two

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 consequences of this proposal. The main ingredients of our analysis are duality symmetries, wall crossing formula and black hole entropy. We use our analysis to constrain the dyon partition function for two hitherto unknown cases -- the partition function of dyons of torsion two (i.e. gcd(Q\wedge P)=2) in heterotic string theory on T^6 and the partition function of dyons carrying untwisted sector electric charge in Z_2 CHL model. With the help of these constraints we propose a candidate for the partition function of dyons of torsion two in heterotic string theory on T^6. This leads to a novel wall crossing formula for decay of quarter BPS dyons into half BPS dyons with non-primitive charge vectors. In an appropriate limit the proposed formula reproduces the known result for the spectrum of torsion two dyons in gauge theory.

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arXiv2008

Tachyon Condensation on Separated Brane-Antibrane System

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 analyzed using level truncated string field theory reproduces the desired property that the dependence of the minimum value of the potential on the initial distance of separation between the branes decreases as we include higher level terms. The rolling tachyon solution constructed using the conformal field theory methods shows that if the initial separation between the branes is less than a critical distance then the solution is described by an exactly marginal deformation of the original conformal field theory where the correlation functions of the deformed theory are determined completely in terms of the correlation functions of the undeformed theory without any need to regularize the theory. Using this we give an expression for the pressure on the brane-antibrane system as a power series expansion in \exp(C x^0) for an appropriate constant C.

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arXiv2007

S-duality Action on Discrete T-duality Invariants

In heterotic string theory compactified on T^6, the T-duality orbits of dyons of charge (Q,P) are characterized by O(6,22;R) invariants Q^2, P^2 and Q.P together with a set of invariants of the discrete T-duality group O(6,22;Z). We study the action of S-duality group on the discrete T-duality invariants and study its consequence for the dyon degeneracy formula. In particular we find that for dyons with torsion r, the degeneracy formula, expressed as a function of Q^2, P^2 and Q.P, is required to be manifestly invariant under only a subgroup of the S-duality group. This subgroup is isomorphic to Γ^0(r). Our analysis also shows that for a given torsion r, all other discrete T-duality invariants are characterized by the elements of the coset SL(2,Z)/Γ^0(r).

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arXiv2007

Linear b-Gauges for Open String Fields

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 that in these linear b-gauges different gauge conditions are needed at different ghost numbers. We derive the full propagator and prove the formal properties which guarantee that the Feynman diagrams reproduce the correct on-shell amplitudes. We find that these properties can fail due to the need to regularize the propagator, and identify a large class of linear b-gauges for which they hold rigorously. In these gauges the propagator has a non-anomalous Schwinger representation and builds Riemann surfaces by adding strip-like domains. Projector-based gauges, like Schnabl's, are not in this class of gauges but we construct a family of regular linear b-gauges which interpolate between Siegel gauge and Schnabl gauge.

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arXiv2007

Duality Orbits, Dyon Spectrum and Gauge Theory Limit of Heterotic String Theory on T^6

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 magnetic charges of the dyon. Using this we can identify the complete set of dyons to which the previously derived degeneracy formula can be extended. By going near special points in the moduli space of the theory we derive the spectrum of quarter BPS dyons in N=4 supersymmetric gauge theory with simply laced gauge groups. The results are in agreement with those derived from field theory analysis.

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arXiv2007

Consistent Truncation to Three Dimensional (Super-)gravity

For a general three dimensional theory of (super-)gravity coupled to arbitrary matter fields with arbitrary set of higher derivative terms in the effective action, we give an algorithm for consistently truncating the theory to a theory of pure (super-)gravity with the gravitational sector containing only Einstein-Hilbert, cosmological constant and Chern-Simons terms. We also outline the procedure for finding the parameters of the truncated theory. As an example we consider dimensional reduction on S^2 of the 5-dimensional minimal supergravity with curvature squared terms and obtain the truncated theory without any curvature squared terms. This truncated theory reproduces correctly the exact central charge of the boundary CFT.

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arXiv2007

Three String Junction and N=4 Dyon Spectrum

The exact spectrum of dyons in a class of N=4 supersymmetric string theories gives us information about dyon spectrum in N=4 supersymmetric gauge theories. This in turn can be translated into prediction about the BPS spectrum of three string junctions on a configuration of three parallel D3-branes. We show that this prediction agrees with the known spectrum of three string junction in different domains in the moduli space separated by walls of marginal stability.

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arXiv2007

Two Centered Black Holes and N=4 Dyon Spectrum

The exact spectrum of dyons in a class of N=4 supersymmetric string theories is known to change discontinuously across walls of marginal stability. We show that the change in the degeneracy across the walls of marginal stability can be accounted for precisely by the entropy of two centered small black holes which disappear as we cross the walls of marginal stability.

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arXiv2007

Rare Decay Modes of Quarter BPS Dyons

The degeneracy of quarter BPS dyons in N=4 supersymmetric string theories is known to jump across walls of marginal stability on which a quarter BPS dyon can decay into a pair of half BPS dyons. We show that as long as the electric and magnetic charges of the original dyon are primitive elements of the charge lattice, the subspaces of the moduli space on which a quarter BPS dyon becomes marginally unstable against decay into a pair of quarter BPS dyons or a half BPS dyon and a quarter BPS dyon are of codimension two or more. As a result any pair of generic points in the moduli space can be connected by a path avoiding these subspaces and there is no jump in the spectrum associated with these subspaces.

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arXiv2007

alpha'-Corrections to Extremal Dyonic Black Holes in Heterotic String Theory

We explicitly compute the entropy of an extremal dyonic black hole in heterotic string theory compactified on T^6 or K3\times T^2 by taking into account all the tree level four derivative corrections to the low energy effective action. For supersymmetric black holes the result agrees with the answer obtained earlier 1) by including only the Gauss-Bonnet corrections to the effective action 2) by including all terms related to the curvature squared terms via space-time supersymmetry transformation, and 3) by using general arguments based on the assumption of AdS_3 near horizon geometry and space-time supersymmetry. For non-supersymmetric extremal black holes the result agrees with the one based on the assumption of AdS_3 near horizon geometry and space-time supersymmetry of the underlying theory.

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arXiv2007

AdS_3, Black Holes and Higher Derivative Corrections

Using AdS/CFT correspondence and the Euclidean action formalism for black hole entropy Kraus and Larsen have argued that the entropy of a BTZ black hole in three dimensional supergravity with (0,4) supersymmetry does not receive any correction from higher derivative terms in the action. We argue that as a consequence of AdS/CFT correspondence the action of a three dimensional supergravity with (0,4) supersymmetry cannot receive any higher derivative correction except for those which can be removed by field redefinition. The non-renormalization of the entropy then follows as a consequence of this and the invariance of Wald's formula under a field redefinition.

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arXiv2007

Adding Charges to N=4 Dyons

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 general charge vectors by considering various charge carrying collective excitations of the original system.

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