G.P. Vacca

The NLO jet vertex for Mueller-Navelet and forward jets: the gluon part

Abstract. In this paper we complete our calculation of the NLO jet vertex which is part of the cross section formulae for the production of Mueller Navelet jets at hadron hadron colliders and of forward jets in deep inelastic electron proton scattering.

On the triple-Pomeron vertex in perturbative QCD

Abstract. We estimate the size of the triple-pomeron vertex in perturbative QCD and compare with the phenomenological value extracted from Regge fits to the experimental data. For simplicity, the results of the QCD analysis are taken in the large-Nc limit. We find that the perturbative triple-pomeron coupling is of the same order of magnitude as the observed one. We also estimate the size of the pomeron self-energy and its contribution to the renormalization of the pomeron intercept. The effect is very small, in agreement with previous non-perturbative estimates.

Energy-momentum tensor of cosmological fluctuations during inflation

We study the renormalized energy-momentum tensor (EMT) of cosmological scalar fluctuations during the slow-rollover regime for chaotic inflation with a quadratic potential and find that it is characterized by a negative energy density which grows during slow-rollover. We also approach the back-reaction problem as a second-order calculation in perturbation theory finding no evidence that the back-reaction of cosmological fluctuations is a gauge artifact. In agreement with the results on the EMT, the average expansion rate is decreased by the back-reaction of cosmological fluctuations.

Vacuum energy, cosmological constant and Standard Model physics

The conditions for the cancellation of one loop contributions to vacuum energy (both U.V. divergent and finite) coming from the Standard Model (SM) fields are examined. It is proven that this is not possible unless one introduces besides several bosons, at least one massive fermion having mass within specific ranges. On examining one of the simplest SM extensions satisfying the constraints one finds that the mass range of the lightest massive boson is compatible with the present Higgs mass bounds. We briefly address the possible treatment of the presence of interactions.

Impact of ultraviolet regularization on the spectrum of curvature perturbations during inflation

Inflationary predictions based on the linear theory of cosmological perturbations are related to the two-point function of a (second quantized) real scalar free field during the accelerated stage. Such a two-point function is finite, in contrast with its coincidence limit, which is divergent due to the ultraviolet divergences proper of field theory. We therefore argue that predictions of most of the inflationary models do not necessarily need a regularization scheme to leading order, i.e. tree level, which is required instead for nonlinear corrections or calculations involving the energy-momentum tensor. We also discuss unpleasant features for the spectrum on demanding its regularization by the traditional fourth order adiabatic subtraction.

Cosmological unparticle correlators

Abstract We introduce and study an extension of the correlator of unparticle matter operators in a cosmological environment. Starting from FRW spaces we specialize to a de Sitter space–time and derive its inflationary power spectrum which we find to be almost flat. We finally investigate some consequences of requiring the existence of a unitary boundary conformal field theory in the framework of the dS/CFT correspondence.

Second Order Gauge-Invariant Perturbations during Inflation

The evolution of gauge invariant second-order scalar perturbations in a general single field inflationary scenario are presented. Different second-order gauge-invariant expressions for the curvature are considered. We evaluate perturbatively one of these second order curvature fluctuations and a second-order gauge-invariant scalar field fluctuation during the slow-roll stage of a massive chaotic inflationary scenario, taking into account the deviation from a pure de Sitter evolution and considering only the contribution of super-Hubble perturbations in mode-mode coupling. The spectra resulting from their contribution to the second order quantum correlation function are nearly scale-invariant, with additional logarithmic corrections with respect to the first order spectrum. For all scales of interest the amplitude of these spectra depends on the total number of e-folds. We find, on comparing first and second order perturbation results, an upper limit to the total number of e-folds beyond which the two orders are comparable.

PT Symmetry and Renormalization in a Pomeron Model

A novel perturbative analysis for the 2+1 local supercritical field theory of pomerons is developed. It is based on the PT symmetry of the model which allows to study a similar Hamiltonian with the same real perturbative spectrum. In the lowest non trivial order of perturbation theory the pomeron interactions are shown to lead to the renormalization of the slope. The appearance of a non local interaction for two pomeron states is such that at small coupling only scattering states are present and the spectrum of two particle states is not affected.

ODDERON IN QCD

A review on how the Odderon idea does appear in QCD is given. In the last years it has been developed a non-perturbative QCD approach based on the stochastic vacuum model and a perturbative one based on resummation techniques in the small x QCD region. Last developments on the perturbative analysis are shown in some details, in particular in application to diffractive eta_c production.

Jet production from the perturbative QCD pomeron with a running coupling constant

An analysis of minijet production from the hard pomeron with a running coupling constant is performed. Two supercritical pomerons found in the numerical study are taken into account. The calculated inclusive jet production rate is finite at small k⊥ and behaves like 1k⊥−4 at high k⊥ modulo factors coming from logarithmic terms. The average k⊥ is found to be very large (∼ 10 – 13 GeV/c) and practically independent of energy. This is interpreted as an indication that at present energies we are still far from the asymptotics and that, apart from supercritical pomerons, other states contribute significantly.