arXiv subjects

P. K. Townsend

Publications and source records attributed to P. K. Townsend.

At least 73 records · Page 4Linked to original sources

arXiv1995

p-Brane Democracy

The ten or eleven dimensional origin of central charges in the N=4 or N=8 supersymmetry algebra in four dimensions is reviewed: while some have a standard Kaluza-Klein interpretation as momenta in compact dimensions, most arise from $p$-form charges in the higher-dimensional supersymmetry algebra that are carried by $p$-brane `solitons'. Although $p=1$ is singled out by superstring perturbation theory, U-duality of N=8 superstring compactifications implies a complete `$p$-brane democracy' of the full non-perturbative theory. An `optimally democratic' perturbation theory is defined to be one in which the perturbative spectrum includes all particles with zero magnetic charge. Whereas the heterotic string is optimally democratic in this sense, the type II superstrings are not, although the 11-dimensional supermembrane might be.

hep-th↗

arXiv1995

Compactification of D=11 supergravity on spaces of exceptional holonomy

We investigate the compactification of D=11 supergravity to D=5,4,3, on compact manifolds of holonomy $SU(3)$ (Calabi-Yau), $G_2$, and $Spin(7)$, respectively, making use of examples of the latter two cases found recently by Joyce. In each case the lower dimensional theory is a Maxwell/Einstein supergravity theory. We find evidence for an equivalence, in certain cases, with heterotic string compactifications from D=10 to D=5,4,3, on compact manifolds of holonomy $SU(2)$ ($K_3\times S^1$), $SU(3)$, and $G_2$, respectively. Calabi-Yau manifolds with Hodge numbers $h_{1,1}=h_{1,2}=19$ play a significant role in the proposed equivalences.

hep-th↗

arXiv1995

Anti-gravitating BPS monopoles and dyons

We show that the exact static, i.e. `anti-gravitating', magnetic multi monopole solutions of the Einstein/Maxwell/dilaton-YM/Higgs equations found by Kastor, London, Traschen, and the authors, for arbitrary non-zero dilaton coupling constant $a$, are equivalent to the string theory BPS magnetic monopole solutions of Harvey and Liu when $a=\sqrt{3}$. For this value of $a$, the monopole solutions also solve the equations of five-dimensional supergravity/YM theory. We also discuss some features of the dyon solutions obtained by boosting in the fifth dimension and some features of the moduli space of anti-gravitating multi-monopoles.

hep-th↗

arXiv1995

String-Membrane Duality in Seven Dimensions

The conjectured equivalence of the heterotic string to a $K_3$ compactified type IIA superstring is combined with the conjectured equivalence of the latter to a compactified 11-dimensional supermembrane to derive a string membrane duality in seven dimensions; the membrane is a soliton of the string theory and vice versa. A prediction of this duality is that the heterotic string is a $K_3$ compactification of the solitonic 11-dimensional fivebrane. It is verified that the worldsheet action of the D=10 heterotic string is indeed obtainable by $K_3$ compactification of the worldvolume action of the 11-dimensional fivebrane, and it is suggested how the worldvolume action of the D=11 supermebrane may be similarly obtained by $T^3$ compactification of the worldvolume action of a D=10 heterotic fivebrane. Generalizations to $D=8$ string-threebrane and membrane-membrane duality are also discussed.

hep-th↗

arXiv1995

The eleven-dimensional supermembrane revisited

It is argued that the type IIA 10-dimensional superstring theory is actually a compactified 11-dimensional supermembrane theory in which the fundamental supermembrane is identified with the the solitonic membrane of 11-dimensional supergravity. The charged extreme black holes of the 10-dimensional type IIA string theory are interpreted as the Kaluza-Klein modes of 11-dimensional supergravity and the dual sixbranes as the analogue of Kaluza-Klein monopoles. All other p-brane solutions of the type IIA superstring theory are derived from the 11-dimensional membrane and its magnetic dual fivebrane soliton.

hep-th↗

arXiv1995

Solitons in supersymmetric sigma-models with torsion

We derive a bound on the energy of the general (p,q)-supersymmetric two-dimensional massive sigma model with torsion, in terms of the topological and Noether charges that appear as central charges in its supersymmetry algebra.The bound is saturated by soliton solutions of first-order Bogomol'nyi-type equations. This generalizes results obtained previously for p=q models without torsion. We give examples of massive (1,1) models with torsion that have a group manifold as a target space. We show that they generically have multiple vacua and find an explicit soliton solution of an SU(2) model. We also construct a new class of zero torsion massive (4,4) models with multiple vacua and soliton solutions. In addition, we compute the metrics on the one-soliton moduli spaces for those cases for which soliton solutions are known explicitly, and discuss their interpretation.

hep-th↗

arXiv1995

Supersymmetric spacetimes in 2+1 adS-supergravity models

We find a class of (2+1)-dimensional spacetimes admitting Killing spinors appropriate to (2,0) adS-supergravity. The vacuum spacetimes include anti-de Sitter (adS) space and charged extreme black holes, but there are many others, including spacetimes of arbitrarily large negative energy that have only conical singularities, and the spacetimes of fractionally charged point particles. The non-vacuum spacetimes are those of self-gravitating solitons obtained by coupling (2,0) adS supergravity to sigma-model matter. We show, subject to a condition on the matter currents (satisfied by the sigma model), and a conjecture concerning global obstructions to the existence of certain types of spinor fields, that the mass of each supersymmetric spacetime saturates a classical bound, in terms of the angular momentum and charge, on the total energy of arbitrary field configurations with the same boundary conditions, although these bounds may be violated quantum mechanically.

gr-qc↗

arXiv1995

Unity of Superstring Dualities

The effective action for type II string theory compactified on a six torus is $N=8$ supergravity, which is known to have an $E_{7}$ duality symmetry. We show that this is broken by quantum effects to a discrete subgroup, $E_7(\Z)$, which contains both the T-duality group $SO(6,6;\Z)$ and the S-duality group $SL(2;\Z)$. We present evidence for the conjecture that $E_7(\Z)$ is an exact \lq U-duality' symmetry of type II string theory. This conjecture requires certain extreme black hole states to be identified with massive modes of the fundamental string. The gauge bosons from the Ramond-Ramond sector couple not to string excitations but to solitons. We discuss similar issues in the context of toroidal string compactifications to other dimensions, compactifications of the type II string on $K_3\times T^2$ and compactifications of eleven-dimensional supermembrane theory.

hep-th↗

arXiv1994

Higher-dimensional resolution of dilatonic black hole singularities

We show that the four-dimensional extreme dilaton black hole with dilaton coupling constant $a= \sqrt{p/(p+2)}$ can be interpreted as a {\it completely non-singular}, non-dilatonic, black $p$-brane in $(4+p)$ dimensions provided that $p$ is {\it odd}. Similar results are obtained for multi-black holes and dilatonic extended objects in higher spacetime dimensions. The non-singular black $p$-brane solutions include the self-dual three brane of ten-dimensional N=2B supergravity and a multi-fivebrane solution of eleven-dimensional supergravity. In the case of a supersymmetric non-dilatonic $p$-brane solution of a supergravity theory, we show that it saturates a bound on the energy per unit $p$-volume.

hep-th↗

arXiv1994

Massive (p,q)-supersymmetric sigma models revisited

We recently obtained the conditions on the couplings of the general two-dimensional massive sigma-model required by (p,q)-supersymmetry. Here we compute the Poisson bracket algebra of the supersymmetry and central Noether charges, and show that the action is invariant under the automorphism group of this algebra. Surprisingly, for the (4,4) case the automorphism group is always a subgroup of SO(3), rather than SO(4). We also reanalyse the conditions for the (2,2) and (4,4) supersymmetry of the zero torsion models without assumptions about the central charge matrix.

hep-th↗

arXiv1994

Macroscopic superstrings as interpolating solitons

It is known that, in string sigma-model metric, the `extreme' fivebrane solution of D=10 supergravity interpolates between D=10 Minkowski spacetime and a supersymmetric $S^3$ compactification to a linear dilaton vacuum. We show here that, in {\it fivebrane} sigma-model metric, the extreme string solution of D=10 supergravity interpolates between Minkowski spacetime and a hitherto unknown supersymmetric $S^7$ compactification of d=10 supergravity to a three-dimensional anti-de Sitter generalization of the linear dilaton vacuum, which may be invariantly characterized in terms of conformal Killing vectors. The dilaton field diverges near the string core but this divergence may be eliminated by re-interpreting the string solution as the extreme membrane solution of 11-dimensional supergravity. We show that the latter has an analytic extension through a regular degenerate event horizon to an interior region containing a curvature singularity. We obtain analogous results for other extended object solutions of supergravity theories.

hep-th↗

arXiv1993

Supersymmetric Self-Gravitating Solitons

We show that the `instantonic' soliton of five-dimensional Yang-Mills theory and the closely related BPS monopole of four-dimensional Yang-Mills/Higgs theory continue to be exact static, and stable, solutions of these field theories even after the inclusion of gravitational, electromagnetic and, in the four-dimensional case, dilatonic interactions, provided that certain non-minimal interactions are included. With the inclusion of these interactions, which would be required by supersymmetry, these exact self-gravitating solitons saturate a gravitational version of the Bogomol'nyi bound on the energy of an arbitrary field configuration.

hep-th↗

arXiv1993

Massive sigma models with (p,q) supersymmetry

We determine the general scalar potential consistent with (p,q) supersymmetry in two-dimensional non-linear sigma models with torsion, generalizing previous results for special cases. We thereby find many new supersymmetric sigma models with potentials, including new (2,2) and (4,4) models.

hep-th↗

arXiv1993

Axionic Defect Anomalies and their Cancellation

We present a simple derivation of the Callan-Harvey-Naculich effect, {\it i.e.} the compensation of charge violation on axion strings due to gauge anomalies by accretion of charge onto the string from the surrounding space. We then show, in the case of axion fields without a potential, that an alternative explanation is possible in which no reference to the surrounding space is necessary because the anomalies are cancelled by a version of the Green-Schwarz mechanism. We prove that such an alternative explanation is always possible in the more general context of p-brane defects in d-dimensional field theories, and hence that there always exists an anomaly-free effective worldvolume action whenever the spacetime theory is anomaly free. Our results have implications, which we discuss, for heterotic and type II fivebranes.

hep-th↗

arXiv1993

Vacuum interpolation in supergravity via super p-branes

We show that many of the recently proposed supersymmetric p-brane solutions of d=10 and d=11 supergravity have the property that they interpolate between Minkowski spacetime and a compactified spacetime, both being supersymmetric supergravity vacua. Our results imply that the effective worldvolume action for small fluctuations of the super p-brane is a supersingleton field theory for $(adS)_{p+2}$, as has been often conjectured in the past.

hep-th↗

arXiv1993

Potentials for (p,0) and (1,1) supersymmetric sigma models with torsion

Using (1,0) superfield methods, we determine the general scalar potential consistent with off-shell (p,0) supersymmetry and (1,1) supersymmetry in two-dimensional non-linear sigma models with torsion. We also present an extended superfield formulation of the (p,0) models and show how the (1,1) models can be obtained from the (1,1)-superspace formulation of the gauged, but massless, (1,1) sigma model.

hep-th↗

arXiv1993

Effective description of axion defects

Axion strings and domain walls exhibit a number of novel effects in the presence of gauge fields, in particular the electromagnetic field. It is shown how these effects are reproduced in a model of Nambu-Goto-type strings and open or closed membranes coupled to gauge fields. The generalization to `axionic p-branes' is considered and it is shown how worldvolume gauge fields that arise in certain cases can be interpreted as Goldstone fields.

hep-th↗

arXiv1992

Low-Temperature Thermodynamics of $A^{(2)}_2$ and su(3)-invariant Spin Chains

We formulate the thermodynamic Bethe Ansatz (TBA) equations for the closed (periodic boundary conditions) $A^{(2)}_2$ quantum spin chain in an external magnetic field, in the (noncritical) regime where the anisotropy parameter $η$ is real. In the limit $η\to 0$, we recover the TBA equations of the antiferromagnetic su(3)-invariant chain in the fundamental representation. We solve these equations for low temperature and small field, and calculate the specific heat and magnetic susceptibility.

hep-th↗