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Nathan Berkovits

Publications and source records attributed to Nathan Berkovits.

At least 127 records · Page 7Linked to original sources
arXiv1997

Extra Dimensions in Superstring Theory

It was earlier shown that an SO(9,1) $θ^\a$ spinor variable can be constructed from RNS matter and ghost fields. $θ^\a$ has a bosonic worldsheet super-partner $λ^\a$ which plays the role of a twistor variable, satisfying $λΓ^μλ= \partial x^μ+iθΓ^μ\partialθ$. For Type IIA superstrings, the left-moving $[θ_L^\a,λ_L^\a]$ and right-moving $[θ_{R\a},λ_{R\a}]$ can be combined into 32-component SO(10,1) spinors $[θ^A,λ^A]$. This suggests that $λ^A Γ^{11}_{AB}λ^B= 2λ_L^\a λ_{R\a}$ can be interpreted as momentum in the eleventh direction. Evidence for this interpretation comes from the zero-momentum vertex operators of the Type IIA superstring and from consideration of $D_0$-branes. As in the work of Bars, one finds an SO(10,2) structure for the Type IIA superstring and an SO(9,1) x SO(2,1) structure for the Type IIB superstring.

hep-th↗
arXiv1996

Local Actions with Electric and Magnetic Sources

Superstring field theory was recently used to derive a covariant action for a self-dual five-form field strength. This action is shown to be a ten-dimensional version of the McClain-Wu-Yu action. By coupling to D-branes, it can be generalized in the presence of sources. In four dimensions, this gives a local Maxwell action with electric and magnetic sources.

hep-th↗
arXiv1996

Super-Maxwell Actions with Manifest Duality

Superstring field theory was recently used to derive a four-dimensional Maxwell action with manifest duality. This action is related to the McClain-Wu-Yu Hamiltonian and can be locally coupled to electric and magnetic sources. In this letter, the manifestly dual Maxwell action is supersymmetrized using N=1 and N=2 superspace. The N=2 version may be useful for studying Seiberg-Witten duality.

hep-th↗
arXiv1996

Manifest Electromagnetic Duality in Closed Superstring Field Theory

The free action for massless Ramond-Ramond fields is derived from closed superstring field theory using the techniques of Siegel and Zwiebach. For the uncompactified Type IIB superstring, this gives a manifestly Lorentz-covariant action for a self-dual five-form field strength. Upon compactification to four dimensions, the action depends on a U(1) field strength from 4D N=2 supergravity. However, unlike the standard Maxwell action, this action is manifestly invariant under the electromagnetic duality transformation which rotates $F_{mn}$ into $ε_{mnpq} F^{pq}$.

hep-th↗
arXiv1996

Super-Poincare Invariant Koba-Nielsen Formulas for the Superstring

The new spacetime-supersymmetric description of the superstring is used to compute tree-level scattering amplitudes for an arbitrary number of massless four-dimensional states. The resulting Koba-Nielsen formula is manifestly SO(3,1) super-Poincare invariant and is easily generalized to scattering in the presence of a D-brane.

hep-th↗
arXiv1996

Off-shell Supersymmetry versus Hermiticity in the Superstring

We point out that off-shell four-dimensional supersymmetry implies strange hermiticity properties for the N=1 RNS superstring. However, these hermiticity properties become natural when the N=1 superstring is embedded into an N=2 superstring.

hep-th↗
arXiv1995

Superspace Effective Actions for 4D Compactifications of Heterotic and Type II Superstrings

Two-dimensional sigma models are defined for the new manifestly spacetime supersymmetric description of four-dimensional compactified superstrings. The resulting target-superspace effective action is constrained by the way the spacetime dilaton couples to the worldsheet curvature: For the heterotic superstring, the worldsheet curvature couples to the real part of a chiral multiplet, and for Type II it couples to the real part of the sum of a vector multiplet and a tensor hypermultiplet. For the Type II superstring, this contradicts the standard folklore that only a hypermultiplet counts string-loops, explains the peculiar dilaton coupling of Ramond-Ramond fields, and allows the effective action to be easily written in N=2 4D superspace. It also implies that vector multiplet interactions get no quantum corrections, while hypermultiplet interactions can only get corrections if mirror symmetry is non-perturbatively broken.

hep-th↗
arXiv1995

New Spacetime-Supersymmetric Methods for the Superstring

In this talk, the new spacetime-supersymmetric description of the superstring is reviewed and some of its applications are described. These applications include the manifestly spacetime-supersymmetric calculation of scattering amplitudes, the construction of a super-Poincaré invariant open superstring field theory, and the beta-function calculation of low-energy equations of motion in superspace. Parts of this work have been done in collaboration with deBoer, van Nieuwenhuizen, Roček, Sezgin, Skenderis, Stelle, and especially, Siegel and Vafa.

hep-th↗
arXiv1995

Super-Poincare Invariant Superstring Field Theory

Using the topological techniques developed in an earlier paper with Vafa, a field theory action is constructed for any open string with critical N=2 worldsheet superconformal invariance. Instead of the Chern-Simons-like action found by Witten, this action resembles that of a Wess-Zumino-Witten model. For the N=2 string which describes (2,2) self-dual Yang-Mills, the string field generalizes the scalar field of Yang. As was shown in recent papers, an N=2 string can also be used to describe the Green-Schwarz superstring in a Calabi-Yau background. In this case, one needs three types of string fields which generalize the real superfield of the super-Yang-Mills prepotential, and the chiral and anti-chiral superfields of the Calabi-Yau scalar multiplet. The resulting field theory action for the open superstring in a Calabi-Yau background has the advantages over the standard RNS action that it is manifestly SO(3,1) super-Poincaré invariant and does not require contact terms to remove tree-level divergences.

hep-th↗
arXiv1994

Vanishing Theorems for the Self-Dual N=2 String

It is proven that up to possible surface terms, the only non-vanishing momentum-dependent amplitudes for the self-dual N=2 string in $R^{2,2}$ are the tree-level two and three-point functions, and the only non-vanishing momentum-independent amplitudes are the one-loop partition function and the tree-level two and four-point functions. The calculations are performed using the topological prescription developed in an earlier paper with Vafa. As in supersymmetric non-renormalization theorems, the vanishing proof is based on a relationship between the zero-momentum dilaton and axion.

hep-th↗
arXiv1994

N=4 Topological Strings

We show how to make a topological string theory starting from an $N=4$ superconformal theory. The critical dimension for this theory is $\hat c= 2$ ($c=6$). It is shown that superstrings (in both the RNS and GS formulations) and critical $N=2$ strings are special cases of this topological theory. Applications for this new topological theory include: 1) Proving the vanishing to all orders of all scattering amplitudes for the self-dual $N=2$ string with flat background, with the exception of the three-point function and the closed-string partition function; 2) Showing that the topological partition function of the $N=2$ string on the $K3$ background may be interpreted as computing the superpotential in harmonic superspace generated upon compactification of type II superstrings from 10 to 6 dimensions; and 3) Providing a new prescription for calculating superstring amplitudes which appears to be free of total-derivative ambiguities.

hep-th↗
arXiv1994

Embeddings for Non-Critical Superstrings

It was previously shown that at critical central charge, $N$-extended superstrings can be embedded in $(N+1)$-extended superstrings. In other words, $(N=0,c=26)\to (N=1,c=15)\to (N=2,c=6)\to (N=3,c=0) \to (N=4,c=0) $. In this paper, we show that similar embeddings are also possible for $N$-extended superstrings at non-critical central charge. For any $x$, the embedding is $(N=0,c=26+x) \to (N=1,c=15+x) \to (N=2,c=6+x) \to (N=3,c=x) \to (N=4,c=x)$. As was conjectured by Vafa, the $(N=2,c=9) \to (N=3,c=3)$ embedding can be used to prove that $N=0$ topological strings are special vaccua of N=1 topological strings.

hep-th↗
arXiv1994

Covariant Quantization of the Green-Schwarz Superstring in a Calabi-Yau Background

After adding a scalar chiral boson to the usual superspace variables, the four-dimensional Green-Schwarz superstring is quantized in a manifestly SO(3,1) super-Poincaré covariant manner. The constraints are all first-class and form an N=2 superconformal algebra with $c=-3$. Since the Calabi-Yau degrees of freedom are described by an N=2 superconformal field theory with $c=9$, the combined Green-Schwarz and Calabi-Yau systems form the $c=6$ matter sector of a critical N=2 string. Using the standard N=2 super-Virasoro ghosts, a nilpotent BRST charge is defined and vertex operators for the massless supermultiplets are constructed. Four-dimensional superstring amplitudes can be calculated with manifest SO(3,1) super-Poincaré invariance by evaluating correlation functions of these BRST-invariant vertex operators on N=2 super-Riemann surfaces.

hep-th↗
arXiv1993

A W-String Realization of the Bosonic String

It has recently been shown that the ordinary bosonic string can be represented by a special background of N=1 or N=2 strings. In this paper, it will be shown that the bosonic string can also be represented by a special background of $W$-strings.

hep-th↗
arXiv1993

On the Uniqueness of String Theory

We show that bosonic strings may be viewed as a particular class of vacua for N=1 superstrings, and N=1 superstrings may be viewed as a particular class of vacua for N=2 strings. Continuing this line of string hierarchies, we are led to search for a universal string theory which includes all the rest as a special vacuum selection.

hep-th↗
arXiv1993

A Ten-Dimensional Super-Yang-Mills Action with Off-Shell Supersymmetry

After adding seven auxiliary scalar fields, the action for ten-dimensional super-Yang-Mills contains an equal number of bosonic and fermionic non-gauge fields. Besides being manifestly Lorentz and gauge-invariant, this action contains nine spacetime supersymmetries whose algebra closes off-shell. Octonions provide a convenient notation for displaying these symmetries.

hep-th↗
arXiv1993

The Ten-Dimensional Green-Schwarz Superstring is a Twisted Neveu-Schwarz-Ramond String

An action for the ten-dimensional Green-Schwarz superstring with N=2 worldsheet superconformal invariance has recently been used to calculate superstring scattering amplitudes and prove their finiteness. In this paper, it is shown that the N=2 stress-energy tensor for this Green-Schwarz action can be constructed out of the stress-energy tensor and ghosts of the Neveu- Schwarz-Ramond action by the standard twisting procedure. In other words, a field redefinition is found from the GS matter fields into the NSR matter and ghost fields which transforms the matter part of the two fermionic GS super- conformal generators into the $b$ ghost and shifted BRST current of the NSR string. In light-cone gauge, this field redefinition reduces to the usual one relating the light-cone GS and NSR fields. Although this proves the equivalence of physical vertex operators in the two superstring formalisms, multiloop amplitudes are easier to calculate using the Green-Schwarz formalism since manifest spacetime supersymmetry eliminates the need for spin cuts, GSO projections, and cutoffs in moduli space.

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