arXiv subjects

E. Dudas

Publications and source records attributed to E. Dudas.

At least 55 records · Page 3Linked to original sources

arXiv2003

On cosmologically induced hierarchies in string theory

We propose, within a perturbative string theory example, a cosmological way to generate a large hierarchy between the observed Planck mass and the fundamental string scale. Time evolution results in three large space dimensions, one additional dimension transverse to our world and five small internal dimensions with a very slow time evolution. The evolution of the string coupling and internal space generate a large Planck mass. However due to an exact compensation between the time evolution of the internal space and that of the string coupling, the gauge and Yukawa couplings on our Universe are time independent.

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arXiv2002

Time and space dependent backgrounds from nonsupersymmetric strings

We investigate maximally symmetric backgrounds in nonsupersymmetric string vacua with D-branes and O-planes localized in the compact space. We find a class of solutions with a perturbative string coupling constant in all regions of spacetime. Depending on the particular model, we find either a time evolution with a big-bang type singularity or a space dependent background with generically orbifold singularities. We show that the result can be interpreted as a supersymmetric bulk with some symmetries broken by the boundaries. We also discuss an interesting connection to Lorentzian and Euclidian orbifolds.

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arXiv2002

Orientifolds of String Theory Melvin backgrounds

We study the dynamics of type I strings on Melvin backgrounds, with a single or multiple twisted two-planes. We construct two inequivalent types of orientifold models that correspond to (non-compact) irrational versions of Scherk-Schwarz type breaking of supersymmetry. In the first class of vacua, D-branes and O-planes are no longer localized in space-time but are smeared along the compact Melvin coordinate with a characteristic profile. On the other hand, the second class of orientifolds involves O-planes and D-branes that are both rotated by an angle proportional to the twist. In case of ``multiple Melvin spaces'', some amount of supersymmetry is recovered if the planes are twisted appropriately and part of the original O-planes are transmuted into new ones. The corresponding boundary and crosscap states are determined.

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arXiv2001

Charged and Uncharged D-branes in various String Theories

We describe how the D-brane spectra of the various ten-dimensional string theories can be related to general properties of the open-closed duality, encoded in the $S$ and $P$ matrices of the conformal field theory. We also complete the classification and the description of non-BPS branes in these string theories, elucidating their non-Abelian structures and the nature of the corresponding super-Higgs mechanisms. We find that the type 0 theories and their orientifolds have two types of uncharged branes, distinguished by their couplings to the closed string tachyon. We also find that the 0A orientifold has the unusual feature of having charged and uncharged branes with identical world-volume dimensions. We conclude with some comments on fractional branes, elucidating their role in connection with the boundary states of $D_{odd}$ SU(2) WZW models.

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arXiv2001

D-branes in String theory Melvin backgrounds

We determine the consistent D-brane configurations in type II nonsupersymmetric Melvin Background. The D-branes are analysed from three complementary points of view: the effective Born-Infeld action, the open string partition function and the boundary state approach. We show the agreement of the results obtained by the three different approaches. Among the surprising features is the existence of supersymmetric branes, some of them having a quasi-periodic direction. We also discuss the generalisation to backgrounds with several magnetic fields, some of them preserving in the closed and the open spectra some amount of supersymmetry. The case of rational magnetic flux, equivalent to freely-acting noncompact orbifolds, is also studied. It allows more possibilities of consistent D-brane configurations.

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arXiv2001

Consistent gravitino couplings in non-supersymmetric strings

The massless spectrum of the ten dimensional USp(32) type I string has an N=1 supergravity multiplet coupled to non-supersymmetric matter. This raises the question of the consistency of the gravitino interactions. We resolve this apparent puzzle by arguing for the existence of a local supersymmetry which is non-linearly realised in the open sector. We determine the leading order low energy effective Lagrangian. Similar results are expected to apply to lower dimensional type I models where supergravity is coupled to non-supersymmetric branes.

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arXiv2000

D-branes in non-tachyonic 0B orientifolds

We determine all D-branes in the non-tachyonic 0'B orientifold, examine their world-volume anomalies and study orbifold compactifications. We find that the spectrum of the D-branes contains chiral fermions in the symmetric, antisymmetric and fundamental representations of (unitary) gauge groups on the branes. The cancellation of the world-volume anomalies requires Wess-Zumino terms which we determine explicitly. We examine a non-tachyonic compactification to 9D whose closed part interpolates between 0B and IIB and revisit compactifications on orbifolds. The D3-brane allows to conjecture, via the AdS/CFT correspondence, a supergravity dual to a non-supersymmetric and infrared-free gauge theory. The D-string gives hints concerning the S-dual of the 0'B orientifold.

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arXiv2000

Type-I strings on magnetised orbifolds and brane transmutation

In the presence of internal magnetic fields, a D9 brane can acquire a D5 (or anti-D5) R-R charge, and can therefore contribute to the corresponding tadpole. In the resulting vacua, supersymmetry is generically broken and tachyonic instabilities are present. However, suitable choices for the magnetic fields, corresponding to self-dual configurations in the internal space, can yield new chiral supersymmetric vacua with gauge groups of reduced rank, where the magnetic energy saturates, partly or fully, the negative tension of the O5+ planes. These models contain Green-Schwarz couplings to untwisted R-R forms not present in conventional orientifolds.

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arXiv2000

Brane solutions in strings with broken supersymmetry and dilaton tadpoles

The tachyon-free nonsupersymmetric string theories in ten dimensions have dilaton tadpoles which forbid a Minkowski vacuum. We determine the maximally symmetric backgrounds for the $USp(32)$ Type I string and the $SO(16)\times SO(16)$ heterotic string. The static solutions exhibit nine dimensional Poincaré symmetry and have finite 9D Planck and Yang-Mills constants. The low energy geometry is given by a ten dimensional manifold with two boundaries separated by a finite distance which suggests a spontaneous compactification of the ten dimensional string theory.

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arXiv1999

String theory predictions for future accelerators

We consider, in a string theory framework, physical processes of phenomenological interest in models with a low string scale. The amplitudes we study involve tree-level virtual gravitational exchange, divergent in a field-theoretical treatment, and massive gravitons emission, which are the main signatures of this class of models. First, we discuss the regularization of summations appearing in virtual gravitational (closed string) Kaluza-Klein exchanges in Type I strings. We argue that a convenient manifestly ultraviolet convergent low energy limit of type I string theory is given by an effective field theory with an arbitrary cutoff $Λ$ in the closed (gravitational) channel and a related cutoff $M_s^2/Λ$ in the open (Yang-Mills) channel. We find the leading string corrections to the field theory results. Second, we calculate exactly string tree-level three and four-point amplitudes with gauge bosons and one massive graviton and examine string deviations from the field-theory result.

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arXiv1999

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.

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arXiv1999

Gauge couplings in four-dimensional Type I string orbifolds

We compute threshold effects to gauge couplings in four-dimensional $Z_N$ orientifold models of type I strings with ${\cal N}=2$ and ${\cal N}=1$ supersymmetry, and study their dependence on the geometric moduli. We also compute the tree-level (disk) couplings of the open sector gauge fields to the twisted closed string moduli of the orbifold in various models and study their effects and that of the one-loop threshold corrections on gauge coupling unification. We interpret the results from the (supergravity) effective theory point of view and comment on the conjectured heterotic-type I duality

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arXiv1999

Brane Supersymmetry Breaking

We show how to construct chiral tachyon-free perturbative orientifold models, where supersymmetry is broken at the string scale on a collection of branes while, to lowest order, the bulk and the other branes are supersymmetric. In higher orders, supersymmetry breaking is mediated to the remaining sectors, but is suppressed by the size of the transverse space or by the distance from the brane where supersymmetry breaking primarily occurred. This setting is of interest for orbifold models with discrete torsion, and is of direct relevance for low-scale string models. It can guarantee the stability of the gauge hierarchy against gravitational radiative corrections, allowing an almost exact supergravity a millimeter away from a non-supersymmetric world.

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arXiv1999

Open Descendants of Z_2\times Z_2 Freely-Acting Orbifolds

We discuss Z_2 \times Z_2 orientifolds where the orbifold twists are accompanied by shifts on momentum or winding lattice states. The models contain variable numbers of D5 branes, whose massless (and, at times, even massive) modes have variable numbers of supersymmetries. We display new type-I models with partial supersymmetry breaking N=2 \to N=1, N=4 \to N=1 and N=4 \to N=2. The geometry of these models is rather rich: the shift operations create brane multiplets related by orbifold transformations that support gauge groups of reduced rank. Some of the models are deformations of six-dimensional supersymmetric type-I models, while others have dual M-theory descriptions.

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arXiv1999

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 $N=4\to N=2$ and $N=4\to N=1$ 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.

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arXiv1998

Supersymmetry breaking, open strings and M-theory

We study supersymmetry breaking by Scherk-Schwarz compactifications in type I string theory. While in the gravitational sector all mass splittings are proportional to a (large) compactification radius, supersymmetry remains unbroken for the massless excitations of D-branes orthogonal to the large dimension. In this sector, supersymmetry breaking can then be mediated by gravitational interactions alone, that are expected to be suppressed by powers of the Planck mass. The mechanism is non perturbative from the heterotic viewpoint and requires a compactification radius at intermediate energies of order 10^{12}-10^{14} GeV. This can also explain the value of Newton's constant if the string scale is close to the unification scale, of order 10^{16} GeV.

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arXiv1998

Report of the GDR working group on the R-parity violation

This report summarizes the work of the "R-parity violation group" of the French Research Network (GDR) in Supersymmetry, concerning the physics of supersymmetric models without conservation of R-parity at HERA, LEP, Tevatron and LHC and limits on R-parity violating couplings from various processes. The report includes a discussion of the recent searches at the HERA experiment, prospects for new experiments, a review of the existing limits, and also theoretically motivated alternatives to R-parity and a brief discussion on the implications of R-parity violation on the neutrino masses.

hep-ph↗

arXiv1998

Pseudo-anomalous U(1) symmetry in the strong coupling limit of the heterotic string

We discuss, in the context of the strongly coupled E_8 \times E_8 heterotic string proposed by Horava and Witten, the appearance of anomalous U(1)_X symmetries of a nonperturbative origin, related to the presence, after compactification, of five-branes in the five-dimensional bulk of the theory. We compute the gauge anomalies and the induced Fayet-Iliopoulos terms on each boundary, which we find to be lower than the universal one induced in the weakly coupled case.

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