arXiv subjects

Keshav Dasgupta

Publications and source records attributed to Keshav Dasgupta.

At least 91 records · Page 5Linked to original sources

arXiv2002

Protected Multiplets of M-Theory on a Plane Wave

We show that the symmetry algebra governing the interacting part of the matrix model for M-theory on the maximally supersymmetric pp-wave is the basic classical Lie superalgebra SU(4|2). We determine the SU(4|2) multiplets present in the exact spectrum in the limit where μ(the mass parameter) becomes infinite, and find that these include infinitely many BPS multiplets. Using the representation theory of SU(4|2), we demonstrate that some of these BPS multiplets, including all of the vacuum states of the matrix model plus certain infinite towers of excited states, have energies which are exactly protected non-perturbatively for any value of μ> 0. In the large N limit, these lead to exact quantum states of M-theory on the pp-wave. We also show explicitly that there are certain BPS multiplets which do receive energy corrections by combining with other BPS multiplets to form ordinary multiplets.

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arXiv2002

Open/Closed String Dualities and Seiberg Duality from Geometric Transitions in M-theory

We propose a general method to study open/closed string dualities from transitions in M theory which is valid for a large class of geometrical configurations. By T-duality we can transform geometrically engineered configurations into N = 1 brane configurations and study the transitions of the corresponding branes by lifting the configurations to M-theory. We describe the transformed degenerated M5 branes and extract the field theory information on gluino condensation by factorization of the Seiberg-Witten curve. We also include massive flavors and orientifolds and discuss Seiberg duality which appears in this case as a birational flop. After the transition, the Seiberg duality becomes an abelian electric-magnetic duality.

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arXiv2002

D3/D7 Inflationary Model and M-theory

A proposal is made for a cosmological D3/D7 model with a constant magnetic flux along the D7 world-volume. It describes an N=2 gauge model with Fayet-Iliopoulos terms and the potential of the hybrid P-term inflation. The motion of the D3-brane towards D7 in a phase with spontaneously broken supersymmetry provides a period of slow-roll inflation in the de Sitter valley, the role of the inflaton being played by the distance between D3 and D7-branes. After tachyon condensation a supersymmetric ground state is formed: a D3/D7 bound state corresponding to an Abelian non-linear (non-commutative) instanton. In this model the existence of a non-vanishing cosmological constant is associated with the resolution of the instanton singularity. We discuss a possible embedding of this model into a compactified M-theory setup.

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arXiv2002

Geometric Transition versus Cascading Solution

We study Vafa's geometric transition and Klebanov - Strassler solution from various points of view in M-theory. In terms of brane configurations, we show the detailed equivalences between the two models. In some limits, both models have an alternative realization as fourfolds in M-theory with appropriate G-fluxes turned on. We discuss some aspects of the fourfolds including how to see the transition and a possible extension to the non-supersymmetric case.

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arXiv2001

Nonlocal Field Theories and their Gravity Duals

The gravity duals of nonlocal field theories in the large N limit exhibit a novel behavior near the boundary. To explore this, we present and study the duals of dipole theories - a particular class of nonlocal theories with fundamental dipole fields. The nonlocal interactions are manifest in the metric of the gravity dual and type-0 string theories make a surprising appearance. We compare the situation to that in noncommutative SYM.

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arXiv2001

M Theory, Orientifolds and G-Flux

We study the properties of M and F theory compactifications to three and four dimensions with background fluxes. We provide a simple construction of supersymmetric vacua, including some with orientifold descriptions. These vacua, which have warp factors, typically have fewer moduli than conventional Calabi-Yau compactifications. The mechanism for anomaly cancellation in the orientifold models involves background RR and NS fluxes. We consider in detail an orientifold of $K3\times T^2$ with background fluxes. After a combination of T and S-dualities, this type IIB orientifold is mapped to a compactification of the SO(32) heterotic string on a non-Kahler space with torsion.

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arXiv2001

Geometric Transition, Large N Dualities and MQCD Dynamics

We study Vafa's geometric transition from a brane setup in M-theory. In this transition D5 branes wrapped on P^1 cycles of a resolved conifold disappear and are replaced by fluxes on a deformed conifold. In the limit of small sized P^1, we describe this mechanism as a transition from curved M5 branes to plane M5 branes which replaces SU(N) MQCD by U(1) theories on the bulk. This agrees with the results expected from the geometric transition. We also discuss the reduction to ten dimensions and a brane creation mechanism in the presence of fluxes.

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arXiv2000

Conifolds with Discrete Torsion and Noncommutativity

We study D3 branes at orbifolded conifold singularities in the presence of discrete torsion. The vacuum moduli space of open strings becomes non-commutative due to a deformation of the superpotential and is studied via the representation theory of the moduli algebra. It is also shown that the center of the moduli algebra correctly describes the underlying orbifolded conifolds. The field theory can be obtained by a marginal deformation of the ${\cal N} = 1$ gauge theory on D3 branes at conifold singularity, the global symmetry being broken from $SU(2) \times SU(2)$ to $U(1) \times U(1)$. By using the AdS/CFT correspondence we argue that the marginal deformation is related to massless KK modes of NSNS and RR two form reduced on the compact space $T^{1,1}$. We build a $T^2$ fibration of $T^{1,1}$ and show that a D3 brane in the bulk correspond to a D5 brane on the $T^2$ fibre. We also discuss the possible brane construction of the system.

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arXiv2000

Pinned Branes and New Non Lorentz Invariant Theories

We describe a mechanism for localising branes in ambient space. When a 3-form flux is turned on in a Taub-NUT space, an M5-brane gets an effective potential that pins it to the center of the space. A similar effect occurs for M2-branes and D-branes with appropriate fluxes. In carefully chosen limits of the external parameters, this leads to new theories that are decoupled from gravity and appear to break Lorentz invariance. For example, we predict the existence of a new 5+1D theory that breaks Lorentz invariance at high-energy and has a low-energy description of N tensor multiplets with (1,0) supersymmetry. We also predict a new type of theory that, similarly to the little-string theory decouples from gravity by a dynamical (rather than kinematical) argument.

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arXiv2000

Noncommutative Tachyons

When unstable Dp-branes in type II string theory are placed in a B-field, the resulting tachyonic world-volume theory becomes noncommutative. We argue that for large noncommutativity parameter, condensation of the tachyon as a noncommutative soliton leads to new decay modes of the Dp-brane into (p-2)-brane configurations, which we interpret as suitably smeared BPS D(p-1)-branes. Some of these configurations are metastable. We discuss various generalizations of this decay process.

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arXiv1999

Brane Constructions, Conifolds and M-Theory

We show that a set of parallel 3-brane probes near a conifold singularity can be mapped onto a configuration of intersecting branes in type IIA string theory. The field theory on the probes can be explicitly derived from this formulation. The intersecting-brane metric for our model is obtained using various dualities and related directly to the conifold metric. The M-theory limit of this model is derived and turns out to be remarkably simple. The global symmetries and counting of moduli are interpreted in the M-theory picture.

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arXiv1999

Brane Constructions, Fractional Branes and Anti-deSitter Domain Walls

Compactifications of type IIB string theory on AdS5 x X5, where X5 is an Einstein space, can have one-fourth or half maximal supersymmetry for certain choices of X5. Some of these theories admit exotic domain walls arising from 5-branes wrapping 2-cycles in X5. We explore the relationship among these domain walls, fractional branes and branes stretched on intervals. World-volume fluxes in the wrapped branes play an important role in the analysis. We draw some parallels between the AdS background with exotic domain walls and N=1 supersymmetric MQCD, and identify other extended objects on the AdS side in the dual brane construction. The process of brane creation is used to give an alternate derivation of the relationship between fractional branes and branes on intervals.

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arXiv1999

Brane mapping under $(-1)^{F_L}$

We present the evidence that $(-1)^{F_L}$ is a nonperturbative symmetry of Type II string theory. We argue that $(-1)^{F_L}$ is a symmetry of string theory as much as the $SL(2, Z)$ of the Type II string is and how the branes are mapped under the $(-1)^{F_L}$ modding. NS branes are mapped into the NS branes with the same world volume dimensions but with the different chiral structure. Supersymmetric Dp-branes (bound with anti-Dp branes) are mapped to unstable nonsupersymmetric Dp-branes, which has D(p-1)-branes as kink solutions according to Horava.

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arXiv1999

Gravitational Couplings and $Z_2$ Orientifolds

The interplay between gravitational couplings on branes and the occurrence of fractional flux in low dimensional orientifolds is examined. It is argued that gravitational couplings need to be assigned not only to D-branes but also to orientifold planes. The fractional charges of the orientifold $d$-planes can be understood in terms of flux quantization of the $d-3$ form potential and modified Bianchi identities. Detailed results are presented for the case of the type IIB orientifold on $T^6/Z_2$, which is dual to F-theory on a complex 4-fold with terminal singularities.

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arXiv1998

Anomaly Inflow on Orientifold Planes

We examine some six-dimensional orientifold models with $N = 1$ supersymmetry, which can be realised as intersecting 7-branes and 7-planes. These models are studied in the light of recent work showing that orientifold planes carry anomalous gravitational couplings on their world-volume. We show that gravitational anomalies can be locally cancelled by these new couplings at every point in the internal space, under the assumption that the anomaly residing on orientifold planes is distributed in a particular way among brane-plane and plane-plane intersections.

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arXiv1997

BPS Nature of 3-String Junctions

We study BPS-saturated classical solutions for the world-sheet theory of a D-string in the presence of a point charge. These solutions are interpreted as describing planar 3-string junctions, which arise because the original D-string is deformed by the presence of the inserted charge. We compute the angles of the junctions and show that the vector sum of string tensions is zero, confirming a conjecture of Schwarz that such configurations are BPS states.

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arXiv1996

A Note on Low-Dimensional String Compactifications

We study supersymmetric compactifications of type II strings on eightfolds to two dimensions. It is demonstrated that the type IIB string on an eightfold is free of gravitational anomalies. T-duality requires that this theory when further compactified on a circle must have a vacuum momentum; this is explicitly shown to be present and to have the right value. A subtlety in the relation of IIB compactifications and M-Theory orientifolds to two dimensions is pointed out.

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arXiv1996

F-Theory at Constant Coupling

The subspace of the moduli space of F-theory on K3 over which the coupling remains constant develops new branches at special values of this coupling. These values correspond to fixed points under the SL(2,Z) duality group of the type IIB string. The branches contain points where K3 degenerates to orbifolds of the four-torus by Z_3,Z_4 and Z_6. A singularity analysis shows that exceptional group symmetries appear on these branches, including pure E_8 xE_8, although SO(32) cannot be realised in this way. The orbifold points can be mapped to a kind of non-perturbative generalization of a IIB orientifold, and to M-theory orbifolds with non-trivial action on 2-brane wrapping modes.

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