Gian Paolo Vacca - Profile on Academia.edu (original) (raw)

Papers by Gian Paolo Vacca

Epj Web of Conferences, 2022

In this paper we extend our recent non perturbative functional renormalization group analysis of ... more In this paper we extend our recent non perturbative functional renormalization group analysis of Reggeon Field Theory to the interactions of Pomeron and Odderon fields. We establish the existence of a fixed point and its universal properties. This analysis, allows to connect the nonperturbative infrared region (large transverse distances) with the UV region of small transverse distances where the high energy limit of perturbative QCD applies. We discuss the implications of result for the existence of an Odderon in high energy scattering.

$Research paper thumbnail of Vacuum energy, Standard Model physics and the <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mn>750</mn><mtext> </mtext><mrow><mi mathvariant="normal">G</mi><mi mathvariant="normal">e</mi><mi mathvariant="normal">V</mi></mrow></mrow><annotation encoding="application/x-tex">750\; \rm{GeV}</annotation></semantics></math>750GeV Diphoton Excess at the LHC$

arXiv (Cornell University), Apr 8, 2016

The conditions for the cancellation of one loop contributions to vacuum energy (both U.V. diverge... more The conditions for the cancellation of one loop contributions to vacuum energy (both U.V. divergent and finite) coming from the known (Standard Model) fields and the field associated with the hypothetical 750 Gev diphoton excess are examined. Depending on the nature of this latter resonance we find that in order to satisfy the constraints (sum rules) different additional, minimal field contributions are required, leading to yet to be observed particles.

The Energy-Momentum Tensor of Quantum Fluctuations in Chaotic Φ2 Inflation

ABSTRACT The study of the renormalized energy-momentum tensor (EMT) of quantum fluctuations in an... more ABSTRACT The study of the renormalized energy-momentum tensor (EMT) of quantum fluctuations in an inflationary universe driven by a massive scalar field is presented and compared with the known results in de Sitter space-time. When metric fluctuations are included, the renormalized EMT is characterized by a negative energy density which grows in time during the inflationary regime. We also approach the back-reaction problem as a second-order calculation in perturbation theory, and find that the average expansion rate is decreased, in agreement with the result on the EMT. Finally, we discuss common concerns and the implications of our results.

Physical review, Nov 17, 2014

There have been some speculations about the existence of critical unitary O(N)-invariant scalar f... more There have been some speculations about the existence of critical unitary O(N)-invariant scalar field theories in dimensions 4 < d < 6 and for large N. Using the functional renormalization group equation, we show that in the lowest order of the derivative expansion, and assuming that the anomalous dimension vanishes for large N , the corresponding critical potentials are either unbounded from below or singular for some finite value of the field.

arXiv (Cornell University), Jan 15, 2020

We discuss the odderon in the QCD and analyze the effects of running coupling introduced in a par... more We discuss the odderon in the QCD and analyze the effects of running coupling introduced in a particular way to preserve the reggeization of the gluon within the leading logarithmic description. This idea is also applied to a family of BKP states with arbitrarily number of gluons in the planar limit. The numerical analysis shows that contrary to the pomeron case where the leading states become discretized, the odderon states still remain a continuous family starting at intercept one. The following rapidity dependence of the amplitude is studied. For the pomeron-odderon system the relation between the descriptions in the reggeized gluon (BFKL) framework and the color dipole/CGC one is investigated.

Journal of Cosmology and Astroparticle Physics, Dec 20, 2018

We study the behaviour of isocurvature perturbations in non-linear sigma models which naturally e... more We study the behaviour of isocurvature perturbations in non-linear sigma models which naturally emerge in supergravity and string inflationary scenarios. We focus on the case of negatively curved field manifolds which can potentially lead to a geometrical destabilisation of isocurvature modes. We find however that heavy fields are stable when their effective mass is computed on the attractor background solution. On the other hand, we show that ultra-light fields can potentially suffer from a geometrical instability when the background trajectory is a geodesic in field space. In this case a full understanding of the system is likely to require the use of non-perturbative methods.

$Research paper thumbnail of Triple pomeron vertex in the limit <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msub><mi>N</mi><mi>c</mi></msub><mo>→</mo><mi mathvariant="normal">∞</mi></mrow><annotation encoding="application/x-tex">N_c\rightarrow\infty</annotation></semantics></math>Nc→∞$

European Physical Journal C, 1999

In the hard pomeron theory with the number of colours N c → ∞ the diffractive amplitude obtained ... more In the hard pomeron theory with the number of colours N c → ∞ the diffractive amplitude obtained in [3] is compared with the results found for N c = 3 in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with k > 2 but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling.

Physical review, Sep 8, 2015

We write a Renormalization Group (RG) equation for the function f in a theory of gravity in the f... more We write a Renormalization Group (RG) equation for the function f in a theory of gravity in the f (R) truncation. Our equation differs from previous ones due to the exponential parametrization of the quantum fluctuations and to the choice of gauge. The cutoff procedure depends on three free parameters, and we find that there exist discrete special choices of parameters for which the flow equation has fixed points where f = f0 + f1R + f2R 2. For other values of the parameters the solution seems to be continuously deformed.

WORLD SCIENTIFIC eBooks, Nov 1, 2021

arXiv (Cornell University), Jul 7, 2021

We discuss the usefulness and theoretical consistency of different entropy variables used in the ... more We discuss the usefulness and theoretical consistency of different entropy variables used in the literature to describe isocurvature perturbations in multifield inflationary models with a generic curved field space. We clarify which is the proper entropy variable to be used to match the evolution of isocurvature modes during inflation to the one after the reheating epoch in order to compare with observational constraints. In particular, we find that commonly used variables, as the relative entropy perturbation or the one associated to the decomposition in tangent and normal perturbations with respect to the inflationary trajectory, even if more useful to perform numerical studies, can lead to results which are wrong by several orders of magnitude, or even to apparent destabilisation effects which are unphysical for cases with light kinetically coupled spectator fields.

Triple pomeron vertex in the limit Nc->8

Eur Phys J C, 1999

The Energy-Momentum Tensor of Quantum Fluctuations in Chaotic Φ 2 Inflation

Thinking, Observing and Mining the Universe, 2004

Nucleation and Atmospheric Aerosols, 2012

The standard field-theoretical approach to the slow-roll inflation is introduced. We then show as... more The standard field-theoretical approach to the slow-roll inflation is introduced. We then show as, in order to calculate the mean square of the canonical gauge invariant quantum fluctuations associated to a generic field, the logarithm of the scale factor has to be used as the time variable in the Fokker-Planck equation in the stochastic approach. Then we compute the growth of different test fields with a small effective mass during slow-roll inflationary models, comparing the results with the one for the gauge invariant canonical fluctuation associated to the inflaton, the Mukhanov variable. We find that in most of the single fields inflationary models such fluctuation grows faster than any test field with a non-negative effective mass, with the exception of hybrid models.

arXiv (Cornell University), Sep 19, 2007

We review some aspects of multiple interactions in High Energy QCD; we discuss in particular AGK ... more We review some aspects of multiple interactions in High Energy QCD; we discuss in particular AGK rules and present some results concerning multiple interactions in the context of jet production.

Starting from the basic path integral in phase space we reconsider the functional approach to the... more Starting from the basic path integral in phase space we reconsider the functional approach to the RG flow of the one particle irreducible effective average action. On employing a balanced coarse-graining procedure for the canonical variables we obtain a functional integral with a non trivial measure which leads to a modified flow equation. We first address quantum mechanics for boson and fermion degrees of freedom and we then extend the construction to quantum field theories. For this modified flow equation we discuss the reconstruction of the bare action and the implications on the computation of the vacuum energy density.

$Research paper thumbnail of Perturbative QCD Odderon and Diffractive η c Production$

The Odderon state in perturbative QCD is briefly reviewed. Recent calculations devoted to estimat... more The Odderon state in perturbative QCD is briefly reviewed. Recent calculations devoted to estimate the diffrative ηc production at high energies from the leading known Odderon states are discussed.

DIFFRACTION 2002: Interpretation of the New Diffractive Phenomena in Quantum Chromodynamics and in the S-Matrix Theory, 2003

The next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet jets ... more The next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet jets production in hadronic collisions and for the forward jet cross section in lepton-hadron collisions are presented in the context of a k t factorizazion formula which resums the leading and next-to-leading logarithms of the energy.

A review of some theoretical aspects of small x QCD physics is given, with a particular emphasis ... more A review of some theoretical aspects of small x QCD physics is given, with a particular emphasis to the relation between the BFKL and the colour dipole approaches. The nonlinear evolution equations one may construct, as a better approximation beyond the linear analysis, are discussed together with their relation to a possible saturation regime.

International Journal of Geometric Methods in Modern Physics, 2020

We consider a functional relation between a given Wilsonian renormalization group (RG) flow, whic... more We consider a functional relation between a given Wilsonian renormalization group (RG) flow, which has to be related to a specific coarse-graining procedure, and an infinite family of (UV cutoff) scale-dependent field redefinitions. Within this framework, one can define a family of Wilsonian proper-time (PT) exact RG equations associated to an arbitrary regulator function. New applications of these RG flow schemes to the Ising Universality class in three dimensions in the derivative expansion are shortly illustrated.

AIP Conference Proceedings, 2017

In the quest for an effective field theory which could help to understand some non perturbative f... more In the quest for an effective field theory which could help to understand some non perturbative feature of the QCD in the Regge limit, we consider a Reggeon Field Theory (RFT) for both Pomeron and Odderon interactions and perform an analysis of the critical theory using functional renormalization group techniques, unveiling a novel symmetry structure.

Epj Web of Conferences, 2022

arXiv (Cornell University), Apr 8, 2016

The Energy-Momentum Tensor of Quantum Fluctuations in Chaotic Φ2 Inflation

Physical review, Nov 17, 2014

arXiv (Cornell University), Jan 15, 2020

Journal of Cosmology and Astroparticle Physics, Dec 20, 2018

European Physical Journal C, 1999

Physical review, Sep 8, 2015

WORLD SCIENTIFIC eBooks, Nov 1, 2021

arXiv (Cornell University), Jul 7, 2021

Triple pomeron vertex in the limit Nc->8

Eur Phys J C, 1999

The Energy-Momentum Tensor of Quantum Fluctuations in Chaotic Φ 2 Inflation

Thinking, Observing and Mining the Universe, 2004

Nucleation and Atmospheric Aerosols, 2012

arXiv (Cornell University), Sep 19, 2007

$Research paper thumbnail of Perturbative QCD Odderon and Diffractive η c Production$

DIFFRACTION 2002: Interpretation of the New Diffractive Phenomena in Quantum Chromodynamics and in the S-Matrix Theory, 2003

International Journal of Geometric Methods in Modern Physics, 2020

AIP Conference Proceedings, 2017

We give a heuristic classification of all universality classes of critical models with up to thre... more We give a heuristic classification of all universality classes of critical models with up to three field-theoretical scalar order parameters in 6− dimensions. Each class is uniquely characterized by its symmetry group and by the set of its universal scaling properties, neither of which are built-in by the formalism but instead emerge nontrivially as outputs of our computations. In particular for three fields we find, apart for a perturbatively unitary solution with O(2) symmetry already known in the literature, five novel non-trivial universality classes with discrete symmetries and with real bounded spectra, among which there is another perturbatively unitary model. We expect them to correspond to new nontrivial CFTs in less than six dimensions.