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- Ashoke Sen
- 1992

â‹† Permanent address 1 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 of motion of low energy effective field theory even after including the scalar and the vector fields, arising due to compactification, in the effectiveâ€¦ (More)

- Ashoke Sen
- 1996

By analyzing F-theory on K3 near the orbifold limit of K3 we establish the equivalence between F-theory on K3 and an orientifold of type IIB on T 2 , which in turn, is related by a T-duality transformation to type I theory on T 2. By analyzing the F-theory background away from the orbifold limit, we show that non-perturbative effects in the orientifoldâ€¦ (More)

- Ashoke Sen
- 1998

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 associated with the potential exactly cancels the sum of the tension of the brane and the anti-brane, thereby giving a configuration of zero energy density and restoring space-timeâ€¦ (More)

- Ashoke Sen
- 1998

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 âˆ’ anti-D-string pair and calculate its mass. We also give a description of this system in terms of an exact boundary conformal field theory and show that in this description this state can be regarded as a non-supersymmetricâ€¦ (More)

- Ashoke Sen
- 2003

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 codimension one BPS D-brane. We study the world-volume theory of massless modes on the kink, and show that the world volume action has precisely the Dirac-Born-Infeld (DBI) form withoutâ€¦ (More)

It has been conjectured that at a stationary point of the tachyon potential for the D-brane of bosonic string theory, the negative energy density exactly cancels the D-brane tension. We evaluate this tachyon potential by off-shell calculations in open string field theory. Surprisingly, the condensation of the tachyon mode alone into the stationary point ofâ€¦ (More)

- Ashoke Sen
- 2005

We study extremal black hole solutions in D dimensions with near horizon geometry AdS2 Ã— S in higher derivative gravity coupled to other scalar, vector and antisymmetric tensor fields. We define an entropy function by integrating the Lagrangian density over S for a general AdS2 Ã—SDâˆ’2 background, taking the Legendre transform of the resulting function withâ€¦ (More)

- Ashoke Sen
- 1999

Using string field theory, we argue that the tachyon potential on a D-brane antiD-brane system in type II string theory in arbitrary background has a universal form, independent of the boundary conformal field theory describing the brane. This implies that if at the minimum of the tachyon potential the total energy of the brane antibrane system vanishes inâ€¦ (More)

- Ashoke Sen
- 1998

In certain regions of the moduli space of K3 and Calabi-Yau manifolds, D-branes wrapped on non-supersymmetric cycles may give rise to stable configurations. We show that in the orbifold limit, some of these stable configurations can be described by solvable boundary conformal field theories. The world-volume theory of N coincident branes of this type isâ€¦ (More)

- Ashoke Sen
- 1999

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 âˆ’ 1)-brane of the same theory. We also speculate on the possibility of obtaining the D-(p âˆ’ 1)-brane as a tachyonic lump on a single D-p-brane. We suggest a possible reinterpretation of the first result which unifies these twoâ€¦ (More)