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Justin R. David

Publications and source records attributed to Justin R. David.

88 records · Page 5Linked to original sources
arXiv2002

Unstable magnetic fluxes in heterotic string theory

We study exact string backgrounds representing a constant magnetic field background in heterotic string theory. These backgrounds are obtained by Kaluza-Klein reduction of a special class of plane wave solutions. For small values of the magnetic field they possess localized closed string tachyons analogous to the Nielsen-Olesen instability of a constant magnetic field in SO(3) Yang-Mills theory. When the magnetic field is embedded in the SO(32) gauge group of the heterotic string it is possible to study the lowest level tachyon in supergravity. We identify the closed string tachyons as fluctuations of the supergravity fields about the background. We argue that the tachyon signals the decay of the background to flat space. Our evidence rests on the study of the closed string tachyon potential, world sheet renormalization group equations in the supergravity approximation and the S-dual of this system in type I theory. In the S-dual description, the closed string tachyons in heterotic string theory correspond to open string tachyons in type I theory. Finally we analyze the non-perturbative stability of these models representing constant magnetic field backgrounds and show that it is stable to pair production of particles.

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arXiv2002

Microscopic Formulation of Black Holes in String Theory

In this Report we review the microscopic formulation of the five dimensional black hole of type IIB string theory in terms of the D1-D5 brane system. The emphasis here is more on the brane dynamics than on supergravity solutions. We show how the low energy brane dynamics, combined with crucial inputs from AdS/CFT correspondence, leads to a derivation of black hole thermodynamics and the rate of Hawking radiation. Our approach requires a detailed exposition of the gauge theory and conformal field theory of the D1-D5 system. We also discuss some applications of the AdS/CFT correspondence in the context of black hole formation in three dimensions by thermal transition and by collision of point particles.

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arXiv2002

Closed String Tachyon Condensation on Twisted Circles

We study IIA/B string theory compactified on twisted circles. These models possess closed string tachyons and reduce to type 0B/A theory in a special limit. Using methods of gauged linear sigma models and mirror symmetry we construct a conformal field theory which interpolates between these models and flat space via an auxiliary Liouville direction. Interpreting motion in the Liouville direction as renormalization group flow, we argue that the end point of tachyon condensation in all these models (including 0B/A theory) is supersymmetric type II theory. We also find a zero-slope limit of these models which is best described in a T-dual picture as a type II NS-NS fluxbrane. In this limit tachyon condensation is an interesting and well posed problem in supergravity. We explicitly determine the tachyon as a fluctuation of supergravity fields, and perform a rudimentary numerical analysis of the relevant flows.

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arXiv2001

Excitations on wedge states and on the sliver

We study ghost number one excitations on the sliver to investigate the solution of string field actions around the tachyon vacuum. The generalized gluing and resmoothing theorem is used to develop a method for evaluating the effective action for excitations on both the wedge states and the sliver state. We analyze the discrete symmetries of the resulting effective action for excitations on the sliver. The gauge unfixed effective action till level two excitations on the sliver is evaluated. This is done for the case with the BRST operator $c_0$ and $c_0 + (c_2 + c_{-2})/2$ with excitations purely in the ghost sector. We find that the values of the effective potential at the local maximum lie close by for the zeroth and the second level of approximation. This indicates that level truncation in string field theory around the tachyon vacuum using excitations on the sliver converges for both choices of the BRST operator. It also provides evidence for the conjectured string field theory actions around the tachyon vacuum.

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arXiv2001

Fermions in Bosonic String Theories

We generalize the Jackiw-Rebbi-Hasenfratz-'t Hooft construction of fermions from bosons to demonstrate the fermionic nature of certain bound states involving SU(N) instantons in even spatial dimensions and SO(N) instantons in $8k+1$ spatial dimensions. We use this result to identify several fermionic excitations in various perturbatively bosonic string theories. In some examples we are able to identify these fermions as excitations in known conformal field theories and independently confirm their fermionic nature. Examples of the fermions we find include certain 3-string junctions in type 0B theory, excitations of the 0-p system in type 0A theory, excitations of the stable D-particle of type O theory, and a rich spectrum of fermions in the bosonic string compactified on the SO(32) group lattice.

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arXiv2001

Tachyon condensation using the disc partition function

It has been recently proposed that the background independent open superstring field theory action is given by the disc partition function with all possible open string operators inserted at the boundary of the disc. We use this proposal to study tachyon condensation in the D0-D2 system. We evaluate the disc partition function for the D0-D2 system in presence of a large Neveu-Schwarz B-field using perturbation theory. This perturbative expansion of the disc partition function makes sense as the boundary tachyon operator for the large Neveu-Schwarz B-field is almost marginal. We find that the mass defect for the formation of the D0-D2 bound state agrees exactly with the expected result in the large B-field limit.

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arXiv2000

U(1) gauge invariance from open string field theory

The naive low energy effective action of the tachyon and the U(1) gauge field obtained from string field theory does not correspond to the world volume action of unstable branes in bosonic string theory. We show that there exists a field redefinition which relates the gauge field and the tachyon of the string field theory action to the fields in the world volume action of unstable branes. We identify a string gauge symmetry which corresponds to the U(1) gauge transformation. This is done to the first non-linear order in the fields. We examine the vector fluctuations at the tachyon condensate till level (4,8).

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arXiv2000

Tachyon condensation in the D0/D4 system

The D0/D4 system with a Neveu-Schwarz B-field in the spatial directions of the D4-brane has a tachyon in the spectrum of the (0,4) strings. The tachyon signals the instability of the system to form a bound state of the D0-brane with the D4-brane. We use the Wess-Zumino-Witten like open superstring field theory formulated by Berkovits to study the tachyon potential for this system. The tachyon potential lies outside the universality class of the D-brane anti-D-brane system. It is a function of the B-field. We calculate the tachyon potential at the zeroth level approximation. The minimum of the tachyon potential in this case is expected to reproduce the mass defect involved in the formation of the D0/D4 bound state. We compare the minimum of the tachyon potential with the mass defect in three cases. For small values of the B-field we obtain 70% of the expected mass defect. For large values of the B-field with Pf$(2πα' B) >0$ the potential reduces to that of the D-brane anti-D-brane reproducing 62% of the expected mass defect. For large values of the B-field with Pf$(2πα' B) <0$ the minimum of the tachyon potential gives 25% of the expected mass defect. At the tachyon condensate we show that the (0,4) strings decouple from the low energy dynamics.

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arXiv2000

Infra-red dynamics of D1-branes at the conifold

We study the infra-red dynamics of D1-branes at the conifold. We show using methods developed to study the infra-red dynamics of (4,4) theories, the infra-red degrees of freedom of the (2,2) theory of a single D1-brane at the conifold is that of a linear dilaton with background charge of $\sqrt{2}$ and a compact scalar. The gauge theory of $N$ D1-branes at the conifold is used to formulate the matrix string in the conifold background.

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arXiv1999

String Theory and Black Holes

This thesis aims to make precise the microscopic understanding of Hawking radiation from the D1/D5 black hole. We present an explict construction of all the shortmultiplets of the ${\cal N}=(4,4)$ SCFT on the symmetric product $\tilde{T}^4/S(Q_1Q_5)$. An investigation of the symmerties of this SCFT enables us to make a one-to-one correspondence beween the supergravity moduli and the marginal opeerators of the SCFT. We analyse the gauge theory dynamics of the splitting of the D1/D5 system into subsystems and show that it agrees with supergravity. We have shown that the fixed scalars of the D1/D5 system couple only to (2,2) operators thus removing earlier discrepancies between D-brane calculations and semiclassical calculations. The absorption cross-section of the minimal scalars is determined from first principles upto a propotionality constant. We show that the absorption cross-section of the minimal scalars computed in supergravity and the SCFT is independent of the moduli.

hep-th↗
arXiv1999

D1/D5 Moduli in SCFT and Gauge Theory, and Hawking Radiation

We construct marginal operators of the orbifold SCFT corresponding to all twenty near-horizon moduli in supergravity, including operators involving twist fields which correspond to the blowing up modes. We identify the operators with the supergravity moduli in a 1-1 fashion by inventing a global SO(4) algebra in the SCFT. We analyze the gauge dynamics of the D1/D5 system relevant to the splitting $(Q_1,Q_5)\to (Q'_1,Q'_5)+ (Q''_1,Q''_5)$ with the help of a linear sigma model. We show in supergravity as well as in SCFT that the absorption cross-section for minimal scalars is the same all over the near-horizon moduli space.

hep-th↗
arXiv1999

Point Mass Geometries, Spectral Flow and AdS_3-CFT_2 Correspondence

We discuss, in terms of the AdS_3-CFT_2 correspondence, a one-parameter family of (asymptotically AdS_3) conical geometries which are generated by point masses and interpolate between AdS_3 and BTZ spacetimes. We show that these correspond to spectral flow in N= (4,4) SCFT_2 which interpolate between NS and R sectors. Our method involves representing the conical spaces as solutions of three-dimensional supergravity based on the supergroup SU(1,1|2) \times SU(1,1|2). The boundary CFT we use is based on the D1/D5 system. The correspondence includes comparing the Euclidean free energies between supergravity and SCFT for the family of conical spaces including BTZ black holes.

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arXiv1998

Absorption and Hawking Radiation of Minimal and Fixed Scalars, and AdS/CFT correspondence

We present a complete derivation of absorption cross-section and Hawking radiation of minimal and fixed scalars from the Strominger-Vafa model of five-dimensional black hole, starting right from the moduli space of the D1-D5 brane system. We determine the precise coupling of this moduli space to bulk modes by using the AdS/CFT correspondence. Our methods resolve a long-standing problem regarding emission of fixed scalars. We calculate three-point correlators of operators coupling to the minimal scalars from supergravity and from SCFT, and show that both vanish. We make some observations about how the AdS/SYM correspondence implies a close relation between large $N$ equations of motion of $d$-dimensional gauge theory and supergravity equations on $AdS_{d+1}$-type backgrounds. We compare with the explicit nonlocal transform relating 1 and 2 dimensions in the context of $c=1$ matrix model.

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arXiv1997

Probing Type I' String Theory Using D0 and D4-Branes

We analyse the velocity-dependent potentials seen by D0 and D4-brane probes moving in Type I' background for head-on scattering off the fixed planes. We find that at short distances (compared to string length) the D0-brane probe has a nontrivial moduli space metric, in agreement with the prediction of Type I' matrix model; however, at large distances it is modified by massive open strings to a flat metric, which is consistent with the spacetime equations of motion of Type I' theory. We discuss the implication of this result for the matrix model proposal for M-theory. We also find that the nontrivial metric at short distances in the moduli space action of the D0-brane probe is reflected in the coefficient of the higher dimensional v^4 term in the D4-brane probe action.

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arXiv1996

Observability of Quantum State of Black Hole

We analyze terms subleading to Rutherford in the $S$-matrix between black hole and probes of successively high energies. We show that by an appropriate choice of the probe one can read off the quantum state of the black hole from the S-matrix, staying asymptotically far from the BH all the time. We interpret the scattering experiment as scattering off classical stringy backgrounds which explicitly depend on the internal quantum numbers of the black hole.

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