119115922
Extracting generalized neutron parton distributions from $^3He$ data
An impulse approximation analysis is described of the generalized parton distributions (GPDs) H and E of the 3He nucleus, quantities which are accessible in hard exclusive processes, such as coherent deeply virtual Compton scattering (DVCS). The calculation is based on the Av18 interaction. The electromagnetic form factors are correctly recovered in the proper limits. The sum of the GPDs H and E of 3He, at low momentum transfer, is largely dominated by the neutron contribution, thanks to the unique spin structure of 3He. This nucleus is therefore very promising for the extraction of the neutron information. By increasing the momentum transfer, however, this conclusion is somehow hindered by the the fast growing proton contribution. Besides, even when the neutron contribution to the GPDs of 3He is largely dominating, the procedure of extracting the neutron GPDs from it could be, in principle, nontrivial. A technique is therefore proposed, independent on both the nuclear potential and the nucleon model used in the calculation, able to take into account the nuclear effects included in the IA analysis and to safely extract the neutron information at values of the momentum transfer large enough to allow the measurements. Thanks to this observation, coherent DVCS should be considered a key experiment to access the neutron GPDs and, in turn, the orbital angular momentum of the partons in the neutron.
118521890
Neutron orbital structure from generalized parton distributions of 3He
The generalized parton distribution H and E of the 3He nucleus, which could be measured in hard exclusive processes, such as coherent deeply virtual Compton scattering, are thoroughly analyzed in impulse approximation, within the Av18 interaction. It is found that their sum is dominated to a large extent by the neutron contribution: The peculiar spin structure of 3He makes this target unique for the extraction of the neutron information. This observation could allow to access for the first time, in dedicated experiments, the orbital angular momentum of the partons in the neutron.
117021213
Studying the neutron orbital structure by coherent hard exclusive processes off 3He
Hard exclusive processes, such as Deeply Virtual Compton Scattering (DVCS), allow to access generalized parton distributions (GPDs). By means of an Impulse Approximation (IA) calculation, it is shown here how, in the low momentum transfer region, the sum of the GPDs H and E is dominated by the neutron contribution. Thanks to this property, 3He could open a new way to access the neutron structure information. In this work, a simple and efficient extraction procedure of the neutron GPDs, able to take into account the nuclear effects included in IA analysis, is proposed.
119281435
Neutron Transverse-Momentum Distributions and Polarized 3He within Light-Front Hamiltonian Dynamics
The possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He is illustrated through an impulse approximation analysis in the Bjorken limit. The generalization of the analysis at finite momentum transfers in a Poincaré covariant framework is outlined. The definition of the light-front spin-dependent spectral function of a J = 1/2 system allows us to show that within the light-front dynamics only three of the six leading twist T-even transverse-momentum distributions are independent.
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.
14243157
Pre-Big Bang scenario on self-T-dual bouncing branes
We consider a new class of five-dimensional dilatonic actions which are invariant under T-duality transformations along three compact coordinates, provided that an appropriate potential is chosen. We show that the invariance remains when we add a boundary term corresponding to a moving 3-brane, and we study the effects of the T-duality symmetry on the brane cosmological equations. We find that T-duality transformations in the bulk induce scale factor duality on the brane, together with a change of sign of the pressure of the brane cosmological matter. However, in a remarkable analogy with the Pre-Big Bang scenario, the cosmological equations are unchanged. Finally, we propose a model where the dual phases are connected through a scattering of the brane induced by an effective potential. We show how this model can realize a smooth, non-singular transition between a pre-Big Bang superinflationary Universe and a post-Big Bang accelerating Universe.
119287029
ASPECTS OF QUANTUM GRAVITY IN COSMOLOGY
We review some aspects of quantum gravity in the context of cosmology. In particular, we focus on models with a phenomenology accessible to current and near-future observations, as the early Universe might be our only chance to peep through the quantum gravity realm.
118633927
The entropy of an acoustic black hole in Bose-Einstein condensates: transverse modes as a cure for divergences
We consider the entropy associated to the phonons generated via the Hawking mechanism in a sonic hole in a Bose–Einstein condensate (BEC). In a previous paper, we looked at the (1+1)-dimensional case both in the hydrodynamic limit and in the case when high-frequency dispersion is taken in account. Here, we extend the analysis, based on the 't Hooft brick wall model, by including transverse excitations. We show that they can cure the infrared divergence that appears in the (1+1)-dimensional case, by acting as an effective mass for the phonons. In the hydrodynamic limit, where high-frequency dispersion is neglected, the ultraviolet divergence remains. On the contrary, in the dispersive case the entropy not only is finite, but it is completely fixed by the geometric parameters of the system.
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.
12251695
Self-T-Dual Brane Cosmology
We show how T-duality can be implemented with brane cosmology. As a result, we obtain a smooth bouncing cosmology with features similar to the ones of the pre-Big Bang scenario. Also, by allowing T-duality transformations along the time-like direction, we find a static solution that displays an interesting self tuning property.