57 research outputs found
On the c-theorem in more than two dimensions
Several pieces of evidence have been recently brought up in favour of the
c-theorem in four and higher dimensions, but a solid proof is still lacking. We
present two basic results which could be useful for this search: i) the values
of the putative c-number for free field theories in any even dimension, which
illustrate some properties of this number; ii) the general form of three-point
function of the stress tensor in four dimensions, which shows some physical
consequences of the c-number and of the other trace-anomaly numbers.Comment: Latex, 7 pages, 1 tabl
String amplitudes in the Hpp-wave limit of AdS3xS3
We compute string amplitudes on pp-waves supported by NS-NS 3-form fluxes and
arising in the Penrose limit of AdS3xS3xM. We clarify the role of the
non-chiral accidental SU(2) symmetry of the background. We comment on the
extension of our results to the superstring and propose a holographic formula
in the BMN limit of the AdS3/CFT2 correspondence valid for any correlator.Comment: Latex,no figures, 47 p
Type I vacua with brane supersymmetry breaking
We show how chiral type I models whose tadpole conditions have no
supersymmetric solution can be consistently defined introducing antibranes with
non-supersymmetric world volumes. At tree level, the resulting stable non-BPS
configurations correspond to tachyon-free spectra, where supersymmetry is
broken at the string scale on some (anti)branes but is exact in the bulk, and
can be further deformed by the addition of brane-antibrane pairs of the same
type. As a result, a scalar potential is generated, that can stabilize some
radii of the compact space. This setting has the novel virtue of linking
supersymmetry breaking to the consistency requirements of an underlying
fundamental theory.Comment: 45 pages. Late
The Leading Eikonal Operator in String-Brane Scattering at High Energy
In this paper we present two (a priori independent) derivations of the eikonal operator in string-brane scattering. The first one is obtained by summing surfaces with any number of boundaries, while in the second one the eikonal operator is derived from the three-string vertex in a suitable light-cone gauge. This second derivation shows that the bosonic oscillators present in the leading eikonal operator are to be identified with the string bosonic oscillators in a suitable light-cone gauge, while the first one shows that it exponentiates recovering unitarity. This paper is a review of results obtained in Refs. [1, 2]
A microscopic description of absorption in high-energy string-brane collisions
G.D. thanks the Galileo Galilei Institute for Theoretical Physics for hospitality and the INFN for partial support while this research was being carried out. G.D. also gratefully acknowledges the hospitality of the Department of Applied Mathematics and Theoretical Physics (Cambridge) at various times during the completion of this work. P. D. thanks C. Maccaferri for discussions on the open-closed string vertex. The research of R. R. is partially supported by STFC (Grant ST/L000415/1, String theory, gauge theory & duality). G.V. would like to acknowledge the hospitality of the Kavli Institute for Theoretical Physics, University of California, Santa Barbara (research supported in part by the National Science Foundation under Grant No. NSF PHY11-25915) where part of this research has been carried out
Partial breaking of supersymmetry, open strings and M-theory
We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N=1 supersymmetry, some models with partial and supersymmetry breaking and their heterotic and M-theory duals. A generic feature of these models is that in the gravitational sector and in the spectrum of D-branes parallel to the breaking coordinate, all mass splittings are proportional to the compactification scale, while global (extended) supersymmetry remains unbroken at tree level for the massless excitations of D-branes transverse to the breaking direction.We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N=1 supersymmetry, some models with partial and supersymmetry breaking and their heterotic and M-theory duals. A generic feature of these models is that in the gravitational sector and in the spectrum of D-branes parallel to the breaking coordinate, all mass splittings are proportional to the compactification scale, while global (extended) supersymmetry remains unbroken at tree level for the massless excitations of D-branes transverse to the breaking direction.We study total and partial supersymmetry breaking by freely acting orbifolds, or equivalently by Scherk-Schwarz compactifications, in type I string theory. In particular, we describe a four-dimensional chiral compactification with spontaneously broken N = 1 supersymmetry, some models with partial N = 4 → N = 2 and N = 4 → N = 1 supersymmetry breaking and their heterotic and M-theory duals. A generic feature of these models is that in the gravitational sector and in the spectrum of D-branes parallel to the breaking coordinate, all mass splittings are proportional to the compactification scale, while global (extended) supersymmetry remains unbroken at tree level for the massless excitations of D-branes transverse to the breaking direction
The abelian cosets of the Heisenberg group
In this paper we study the abelian cosets of the H(4) WZW model. They
coincide or are related to several interesting three-dimensional backgrounds
such as the Melvin model, the conical point-particle space-times and the null
orbifold. We perform a detailed CFT analysis of all the models and compute the
coset characters as well as some typical three-point couplings of coset
primaries.Comment: 26 pages; v2: minor typos corrected, also added section 3.3 and 4.3
with a few comments on a third class of geometries that have not been
discussed in v
The diagonal cosets of the Heisenberg group
In this paper we study the diagonal cosets of the non-compact H4 WZW model.
Generalising earlier work by Antoniadis and Obers, we provide an exact
world-sheet description for several families of non-maximally symmetric
gravitational plane waves with background NS fluxes. We show that the
sigma-models that correspond to an asymmetric action of the gauge group
smoothly interpolate between singular and non-singular plane waves. We also
analyse the representations of the coset chiral algebra and derive the spectrum
of all the models.Comment: 42 pages, v2: more explicit expressions for the background fields in
section 3.2.2, reference [49] added, some typos correcte
Landau-Ginzburg Description of Boundary Critical Phenomena in Two Dimensions
The Virasoro minimal models with boundary are described in the
Landau-Ginzburg theory by introducing a boundary potential, function of the
boundary field value. The ground state field configurations become non-trivial
and are found to obey the soliton equations. The conformal invariant boundary
conditions are characterized by the reparametrization-invariant data of the
boundary potential, that are the number and degeneracies of the stationary
points. The boundary renormalization group flows are obtained by varying the
boundary potential while keeping the bulk critical: they satisfy new selection
rules and correspond to real deformations of the Arnold simple singularities of
A_k type. The description of conformal boundary conditions in terms of boundary
potential and associated ground state solitons is extended to the N=2
supersymmetric case, finding agreement with the analysis of A-type boundaries
by Hori, Iqbal and Vafa.Comment: 42 pages, 13 figure
Isometric Embeddings and Noncommutative Branes in Homogeneous Gravitational Waves
We characterize the worldvolume theories on symmetric D-branes in a
six-dimensional Cahen-Wallach pp-wave supported by a constant Neveu-Schwarz
three-form flux. We find a class of flat noncommutative euclidean D3-branes
analogous to branes in a constant magnetic field, as well as curved
noncommutative lorentzian D3-branes analogous to branes in an electric
background. In the former case the noncommutative field theory on the branes is
constructed from first principles, related to dynamics of fuzzy spheres in the
worldvolumes, and used to analyse the flat space limits of the string theory.
The worldvolume theories on all other symmetric branes in the background are
local field theories. The physical origins of all these theories are described
through the interplay between isometric embeddings of branes in the spacetime
and the Penrose-Gueven limit of AdS3 x S3 with Neveu-Schwarz three-form flux.
The noncommutative field theory of a non-symmetric spacetime-filling D-brane is
also constructed, giving a spatially varying but time-independent
noncommutativity analogous to that of the Dolan-Nappi model.Comment: 52 pages; v2: References adde
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