arXiv subjects

Nathan Berkovits

Publications and source records attributed to Nathan Berkovits.

At least 109 records · Page 6Linked to original sources

arXiv2000

A New Description of the Superstring

This is a review of the new manifestly spacetime-supersymmetric description of the superstring. The new description contains N=2 worldsheet supersymmetry, and is related by a field redefinition to the standard RNS description. It is especially convenient for four-dimensional compactifications since SO(3,1) super-Poincaré invariance can be made manifest. Parts of this work have been done in collaboration with Warren Siegel and Cumrun Vafa. This review is based on lectures given at the VIII J.A. Swieca summer school and should be easily accesible to anyone familiar with the RNS superstring description.

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arXiv2000

Cohomology in the Pure Spinor Formalism for the Superstring

A manifestly super-Poincaré covariant formalism for the superstring has recently been constructed using a pure spinor variable. Unlike the covariant Green-Schwarz formalism, this new formalism is easily quantized with a BRST operator and tree-level scattering amplitudes have been evaluated in a manifestly covariant manner. In this paper, the cohomology of the BRST operator in the pure spinor formalism is shown to give the usual light-cone Green-Schwarz spectrum. Although the BRST operator does not directly involve the Virasoro constraint, this constraint emerges after expressing the pure spinor variable in terms of SO(8) variables.

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arXiv2000

Consistency of Super-Poincare Covariant Superstring Tree Amplitudes

Using pure spinors, the superstring was recently quantized in a manifestly ten-dimensional super-Poincaré covariant manner and a covariant prescription was given for tree-level scattering amplitudes. In this paper, we prove that this prescription is cyclically symmetric and, for the scattering of an arbitrary number of massless bosons and up to four massless fermions, it agrees with the standard Ramond-Neveu-Schwarz prescription.

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arXiv2000

Tachyon Condensation in Superstring Field Theory

It has been conjectured that at the stationary point of the tachyon potential for the D-brane-anti-D-brane pair or for the non-BPS D-brane of superstring theories, the negative energy density cancels the brane tensions. We study this conjecture using a Wess-Zumino-Witten-like open superstring field theory free of contact term divergences and recently shown to give 60% of the vacuum energy by condensation of the tachyon field alone. While the action is non-polynomial, the multiscalar tachyon potential to any fixed level involves only a finite number of interactions. We compute this potential to level three, obtaining 85% of the expected vacuum energy, a result consistent with convergence that can also be viewed as a successful test of the string field theory. The resulting effective tachyon potential is bounded below and has two degenerate global minima. We calculate the energy density of the kink solution interpolating between these minima finding good agreement with the tension of the D-brane of one lower dimension.

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arXiv2000

The Tachyon Potential in Open Neveu-Schwarz String Field Theory

A classical action for open superstring field theory has been proposed which does not suffer from contact term problems. After generalizing this action to include the non-GSO projected states of the Neveu-Schwarz string, the pure tachyon contribution to the tachyon potential is explicitly computed. The potential has a minimum of $V = -{1\over{32 g^2}}$ which is 60% of the predicted exact minimum of $V=-{1\over{2π^2 g^2}}$ from D-brane arguments.

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arXiv2000

Super-Poincare Covariant Quantization of the Superstring

Using pure spinors, the superstring is covariantly quantized. For the first time, massless vertex operators are constructed and scattering amplitudes are computed in a manifestly ten-dimensional super-Poincaré covariant manner. Quantizable non-linear sigma model actions are constructed for the superstring in curved backgrounds, including the $AdS_5\times S^5$ background with Ramond-Ramond flux.

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arXiv2000

Four-Point Amplitude from Open Superstring Field Theory

An open superstring field theory action has been proposed which does not suffer from contact term divergences. In this paper, we compute the on-shell four-point tree amplitude from this action using the Giddings map. After including contributions from the quartic term in the action, the resulting amplitude agrees with the first-quantized prescription.

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arXiv1999

A New Approach to Superstring Field Theory

I review the construction of an action for open superstring field theory which does not suffer from the contact term problems of other approaches. I also discuss a possible generalization of this action for closed superstring field theory.

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arXiv1999

Quantization of the Superstring in Ramond-Ramond Backgrounds

Sigma model actions are constructed for the Type II superstring compactified to four and six dimensional curved backgrounds which can contain non-vanishing Ramond-Ramond fields. These actions are N=2 worldsheet superconformally invariant and can be covariantly quantized preserving manifest spacetime supersymmetry. They are constructed using a hybrid version of superstring variables which combines features of the Ramond-Neveu-Schwarz and Green-Schwarz formalisms. For the $AdS_2\times S^2$ and $AdS_3\times S^3$ backgrounds, these actions differ from the classical Greeen-Schwarz actions by a crucial kinetic term for the fermions. Parts of this work have been done in collaborations with M. Bershadsky, T. Hauer, W. Siegel, C. Vafa, E. Witten, S. Zhukov and B. Zwiebach.

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arXiv1999

Quantization of the Type II Superstring in a Curved Six-Dimensional Background

A sigma model action with N=2 D=6 superspace variables is constructed for the Type II superstring compactified to six curved dimensions with Ramond-Ramond flux. The action can be quantized since the sigma model is linear when the six-dimensional spacetime is flat. When the six-dimensional spacetime is $AdS_3\times S^3$, the action reduces to one found earlier with Vafa and Witten.

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arXiv1999

Quantization of the Superstring with Manifest U(5) Super-Poincare Invariance

The superstring is quantized in a manner which manifestly preserves a U(5) subgroup of the (Wick-rotated) ten-dimensional super-Poincaré invariance. This description of the superstring contains critical N=2 worldsheet superconformal invariance and is a natural covariantization of the U(4)-invariant light-cone Green-Schwarz description.

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arXiv1998

Type IIB $R^4 H^{4g-4}$ Conjectures

We propose $SL(2,Z)$ (and $SL(3,Z)$) invariant conjectures for all $R^4 H^{4g-4}$ couplings of Type IIB strings on $R^{10}$ (and $R^{8}\times T^2$), generalizing conjectures of Green and Gutperle (and Kiritsis and Pioline) for the $R^4$ coupling. A strong check for our conjectures is that on $T^2$ at weak coupling, they reproduce the multiloop scattering amplitudes which had been previously computed using N=2 strings in the N=4 topological formalism. Applications to $(p,q)$ string production in a background $H$ field, generalizing Schwinger's computation for pair production in constant $F$ field, are suggested.

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arXiv1998

Conformal Compensators and Manifest Type IIB S-Duality

Using the conformal compensator superfields of N=2 D=4 supergravity, the Type IIB S-duality transformations are expressed as a linear rotation which mixes the compensator and matter superfields. The classical superspace action for D=4 compactifications of Type IIB supergravity is manifestly invariant under this transformation. Furthermore, the introduction of conformal compensators allows a Fradkin-Tseytlin term to be added to the manifestly SL(2,Z)-covariant sigma model action of Townsend and Cederwall.

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arXiv1997

A Problem with the Superstring Action of Deriglazov and Galajinsky

Deriglazov and Galajinsky have recently proposed a new covariant action for the Green-Schwarz superstring which can be constructed in any spacetime dimension. In this short note, I show that their action contains extra on-shell degrees of freedom as compared with the standard action, and is therefore inequivalent.

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arXiv1997

On the Picture Dependence of Ramond-Ramond Cohomology

Closed string physical states are BRST cohomology classes computed on the space of states annihilated by $b_0^-$. Since $b_0^-$ does not commute with the operations of picture changing, BRST cohomologies at different pictures need not agree. We show explicitly that Ramond-Ramond (RR) zero-momentum physical states are inequivalent at different pictures, and prove that non-zero momentum physical states are equivalent in all pictures. We find that D-brane states represent BRST classes that are nonpolynomial on the superghost zero modes, while RR gauge fields appear as polynomial BRST classes. We also prove that in $x$-cohomology, the cohomology where the zero mode of the spatial coordinates is included, there is a unique ghost-number one BRST class responsible for the Green-Schwarz anomaly, and a unique ghost number minus one BRST class associated with RR charge.

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arXiv1997

Duality-Symmetric Eleven-Dimensional Supergravity and its Coupling to M-Branes

The standard eleven-dimensional supergravity action depends on a three-form gauge field and does not allow direct coupling to five-branes. Using previously developed methods, we construct a covariant eleven-dimensional supergravity action depending on a three-form and six-form gauge field in a duality-symmetric manner. This action is coupled to both the M-theory two-brane and five-brane, and corresponding equations of motion are obtained. Consistent coupling relates D=11 duality properties with self-duality properties of the M-5-brane. From this duality-symmetric formulation, one can derive an action describing coupling of the M-branes to standard D=11 supergravity.

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arXiv1997

Construction of $R^4$ Terms in N=2 D=8 Superspace

Using linearized superfields, $R^4$ terms in the Type II superstring effective action compactified on $T^2$ are constructed as integrals in N=2 D=8 superspace. The structure of these superspace integrals allows a simple proof of the $R^4$ non-renormalization theorems which were first conjectured by Green and Gutperle.

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arXiv1997

An Introduction to Superstring Theory and its Duality Symmetries

In these proceedings for the First School on Field Theory and Gravitation (Vitória, Brasil), a brief introduction is given to superstring theory and its duality symmetries. This introduction is intended for beginning graduate students with no prior knowledge of string theory.

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