120477826
Spin structures, spinors and the Dirac operator: real versus complex manifolds
Abstract We describe the relation between spin-structures, spinors and the Dirac operator on a (real) manifold and the analogous definitions in complex holomorphic terms. This may be useful for physicists interested in the algebraic geometric approach to superstrings.
117730967
Generalized Wess-Zumino terms and global anomalies in string sigma models
6392662
Loop and Path Spaces and¶Four-Dimensional BF Theories:¶Connections, Holonomies and Observables
Abstract: We study the differential geometry of principal G-bundles whose base space is the space of free paths (loops) on a manifold M. In particular we consider connections defined in terms of pairs (A,B), where A is a connection for a fixed principal bundle P(M,G) and B is a 2-form on M. The relevant curvatures, parallel transports and holonomies are computed and their expressions in local coordinates are exhibited. When the 2-form B is given by the curvature of A, then the so-called non-abelian Stokes formula follows.For a generic 2-form B, we distinguish the cases when the parallel transport depends on the whole path of paths and when it depends only on the spanned surface. In particular we discuss generalizations of the non-abelian Stokes formula. We study also the invariance properties of the (trace of the) holonomy under suitable transformation groups acting on the pairs (A,B).In this way we are able to define observables for both topological and non-topological quantum field theories of the BF type. In the non-topological case, the surface terms may be relevant for the understanding of the quark-confinement problem. In the topological case the (perturbative) four-dimensional quantum BF-theory is expected to yield invariants of imbedded (or immersed) surfaces in a 4-manifold M.
119943646
Relation between representations of KN and virasoro algebras
Abstract Some aspects of conformal field theory over Riemann surfaces are examined. We study, in particular, on simple systems (b−c systems) the relation between representations of the Virasoro and the KN algebras. KN algebra representations decompose into an infinite sum of the Virasoro algebra representations. We argue that the KN algebra representations are the right tool in order to classify conformal field theories over higher genus Riemann surfaces.
117924192
Generalized wess-zumino terms
121725055
Conformal invariance on a generic Riemann surface in the presence of a non-flat background metric
Abstract By using bases of meromorphic differentials, recently proposed by Krichever and Novikov, we calculate the brackets of the moments of the energy-momentum tensor of a bosonic string theory in the presence of a generic target metric. To do this we expand the target metric in normal coordinates. To the lowest perturbative order we find that the BRST operator is nilpotent if we impose the condition that the Ricci tensor of the target metric vanish.
34037354
RF system for the elettra new full energy booster injector
The Elettra new full energy injector will be based on a 100 MeV linac and a 2.5 GeV booster synchrotron and it will replace the existing 1.2 linac injector. This paper presents the design, construction and the test results of the RF system for the booster synchrotron. The analysis of the foreseen operating scenario is also described. The system must be as simple and reliable as possible, taking into consideration the high availability required for the possible top-up mode of operation. It has also to be consistent with the other upgrades of the facility, as the upgrade of the storage ring RF system. The booster RF system will use a 500 MHz 5-cell copper cavity powered by a 60 kW klystron based power plant. The low level electronics has been in-house developed, starting from the system in operation in the storage ring, increasing the performances and developing the new features required by the use of a five-cell cavity, instead of a single cell one, and by the ramped operation. The commissioning of the new injector is scheduled to start in summer 2007, while the first Elettra operation for users with the new full energy injector is expected for the first quarter of 2008.
118638108
Superluminal dispersion relations and the Unruh effect
In the context of quantum gravity phenomenology, we study the Unruh effect in the presence of superluminal dispersion relations. In particular, we estimate the response function and the probability rate for an accelerated detector coupled to a massless scalar field, whose dispersion relation becomes essentially quadratic beyond a threshold momentum ${k}_{p}$. By means of a perturbative analysis, we show that superluminal dispersion induces a correction to the Planckian spectrum, which tends to vanish as ${k}_{p}$ increases.
49385697
INSTALLATION AND COMMISSIONING OF THE RF SYSTEM FOR THE NEW ELETTRA BOOSTER
The commissioning of the new booster of the Elettra synchrotron radiation storage ring started in Fall 2007. The RF system of the booster is made of a five cells accelerating cavity fed by a 60 kW 500 MHz power plant. The accelerating cavity voltage is ramped along with the booster energy at repetition rate 3 Hz. The cavity field is controlled by analog feedback loops on amplitude, phase and the resonant frequency. This paper describes the setting into operation of the system and its performances during the commissioning phase of the machine.
119259600
Generalized Parton Distributions of 3He and the Neutron Orbital Structure
The two leading twist, quark helicity conserving generalized parton distributions (GPDs) of 3He, accessible, for example, in coherent deeply virtual Compton scattering (DVCS), are calculated in impulse approximation (IA). Their sum, at low momentum transfer, is found to be largely dominated by the neutron contribution, so that 3He is very promising for the extraction of the neutron information. Anyway, such an extraction could be not trivial. A technique, able to take into account the nuclear effects included in the IA analysis in the extraction procedure, even at moderate values of the momentum transfer, is proposed. Coherent DVCS arises therefore as a crucial experiment to access, for the first time, the neutron GPDs and the orbital angular momentum of the partons in the neutron.
9318966
Toroidal black holes and T-duality
Abstract We consider the toroidal black holes that arise as a generalization of the AdS5×S5 solution of type IIB supergravity. The symmetries of the horizon space allow T-duality transformations that can be exploited to generate new inequivalent black hole solutions of both type IIB and type IIA supergravity, with non-trivial dilaton, B-field, and RR-forms. We examine the asymptotic structure and thermodynamical properties of these solutions.