119288395
A new approach to non-commutative inflation
We propose an inflationary scenario inspired by a recent formulation, in terms of coherent states, of non-commutative quantum field theory. We consider the semiclassical Einstein equations, and exploit the ultraviolet finiteness of the non-commutative propagator to construct the expectation value of the energy–momentum tensor associated with a generic scalar field. It turns out that the latter is always finite and dominated by an effective cosmological constant. By combining this general feature with the intrinsic fuzziness of spacetime, we show that non-commutativity governs the energy density of the early Universe in such a way that the strong energy condition is violated. Thus, there might be a bounce and a subsequent inflationary phase, which does not need any ad hoc scalar field.
16113420
Self-T-dual brane cosmology and the cosmological constant problem
We consider a codimension-one brane embedded in a gravity-dilaton bulk action, whose symmetries are compatible with T-duality along the space-like directions parallel to the brane, and the bulk time-like direction. The equations of motions in the string frame allow for a smooth background obtained by the union of two symmetric patches of AdS space. The Poincare invariance of the solution appears to hold independently of the value of the brane vacuum energy, through a self-tuning property of the dilaton ground state. Moreover, the effective cosmology displays a bounce, at which the scale factor does not shrink to zero. Finally, by exploiting the T-duality symmetry, we show how to construct an ever-expanding Universe, along the lines of the Pre-Big-Bang scenario.
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.
119224226
Entropy of an acoustic black hole in Bose-Einstein condensates
We compute the entanglement entropy associated to the Hawking emission of a $(1+1)$-dimensional acoustic black hole in a Bose-Einstein condensate. We use the brick wall model proposed by 't Hooft, adapted to the momentum space, in order to tackle the case when high frequency dispersion is taken in account. As expected, we find that in the hydrodynamic limit the entropy only depends on the size of the box in the near-horizon region, as for gravitational $(1+1)$-dimensional black holes. When dispersion effects are considered, we find a correction that depends on the square of the size of the near-horizon region measured in units of healing length, very similar to the universal correction to the entropy found in the case of spin-1/2 Heisenberg XX chains.
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.
18733372
Bubbles in anti-de Sitter space
We explore the bubble spacetimes which can be obtained from double analytic continuations of static and rotating black holes in anti-de Sitter space. In particular, we find that rotating black holes with elliptic horizon lead to bubble spacetimes only in dimension greater than five. For dimension greater than seven, the topology of the bubble can be non-spherical. However, a bubble spacetime is shown to arise from a rotating de Sitter black hole in four dimensions. In all cases, the evolution of the bubble is of de Sitter type. Double analytic continuations of hyperbolic black holes and branes are also discussed.
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.
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.
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.
53510047
Double parton correlations in constituent quark models
We thank Markus Diehl for fruitful comments. S. S. thanks Livio Fano for useful discussions. This work was supported in part by the Research Infrastructure Integrating Activity Study of Strongly Interacting Matter (acronym HadronPhysic3, Grant Agreements No. 283286 and No. 283288) under the Seventh Framework Programme of the European Community, by the Mineco under Contract No. FPA2010-21750-C02-01, by GVA-Prometeo/2009/129, and by CPAN(CSD-00042). S. S. thanks the Department of Theoretical Physics of the University of Valencia for warm hospitality and the IVICFA and the project "Partonic structure of mesons, nucleons and light nuclei" of the INFN-Mineco agreement for financial support. V. V. thanks the INFN, sezione di Perugia and the Department of Physics of the University of Perugia for warm hospitality and support.
8554040
BRST symmetries for the tangent gauge group
For any principal bundle P, one can consider the subspace of the space of connections on its tangent bundle TP given by the tangent bundle TA of the space of connections A on P. The tangent gauge group acts freely on TA. Appropriate BRST operators are introduced for quantum field theories that include as fields elements of TA, as well as tangent vectors to the space of curvatures. As the simplest application, the BRST symmetry of the so-called BF-Yang–Mills theory is described and the relevant gauge fixing conditions are analyzed. A brief account on the topological BF theories is also included and the relevant Batalin–Vilkovisky operator is described.