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R. Gatto

Publications and source records attributed to R. Gatto.

At least 37 records · Page 2Linked to original sources
arXiv2003

Quasi-particle Specific Heats for the Crystalline Color Superconducting Phase of QCD

We calculate the specific heats of quasi-particles of two-flavor QCD in its crystalline phases for low temperature. We show that for the different crystalline structures considered here there are gapless modes contributing linearly in temperature to the specific heat. We evaluate also the phonon contributions which are cubic in temperature. These features might be relevant for compact stars with an inner shell in a color superconducting crystalline phase.

hep-ph↗
arXiv2003

Aspects of the Color Flavor Locking phase of QCD in the Nambu-Jona Lasinio approximation

We study two aspects of the CFL phase of QCD in the NJL approximation. The first one is the issue of the dependence on μof the ultraviolet cutoff in the gap equation, which is solved allowing a running coupling constant. The second one is the dependence of the gap on the strange quark mass; using the high density effective theory we perform an expansion in the parameter (m_s/μ)^2 after checking that its numerical validity is very good already at first order.

hep-ph↗
arXiv2002

Massive quark effects in two flavor color superconductors

The high density effective theory formalism (HDET) is employed to describe high density QCD with two massive flavors (2SC). The gap equation is derived and explicitly solved for the gap parameter. The parameters associated to the pseudo Nambu-Goldstone boson of $U(1)_A$ are evaluated in the limit $μ\to\infty$ and $m/μ$ fixed. In particular we find for the velocity of the NG boson the relation $v^2=\sqrt{μ_1^2-m_1^2}\sqrt{μ_2^2-m_2^2}/3μ_1μ_2$.

hep-ph↗
arXiv2002

Anisotropy Parameters for the Effective Description of Crystalline Color Superconductors

In the high density low temperature limit, Quantum Chromodynamics (QCD) exhibits a transition to a phase characterized by color superconductivity and by energy gaps in the fermion spectra. Under specific circumstances the gap parameter has a crystalline pattern, breaking translational and rotational invariance. The corresponding phase is the the crystalline color superconductive phase (or {\it LOFF} phase). In the effective theory the fermions couple to the phonon arising from the breaking of rotation and translation invariance. We compute the parameters of the low energy effective lagrangian describing the motion of the free phonon in the high density medium and derive the phonon dispersion law.

hep-ph↗
arXiv2002

Phonons and gluons in the crystalline color superconducting phase of QCD

The High Density Effective Theory formalism is used to calculate the low energy properties of the phonons and gluons in the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of two-flavor QCD. The effective phonon Lagrangian for the cubic crystal structure, which is favored according to a recent study, depends, at the second order in the derivatives, on three parameters which we calculate in this paper. We also compute for soft momenta the effective lagrangian for the gluons of the unbroken SU(2)_c group, both for a single plane wave structure and for the cube. In both cases the Meissner gluon mass vanishes as in the case of complete isotropy; on the other hand there is a partial Debye screening due to the existence of blocking regions on the Fermi spheres. For the single plane wave structure the gluon dielectric tensor is non isotropic, while it is isotropic for the cubic crystal, in spite of the intrinsic anisotropy of the structure.

hep-ph↗
arXiv2002

Crystalline Color Superconductivity: Effective Lagrangian and Phonon Dispersion Law

The recent study by Bowers and Rajagopal on the possible structures for the QCD crystalline color superconducting phase favors a cubic structure and allows for a first discussion of the QCD dynamics in the crystalline phase. The cubic structure leads to complete breaking of traslation invariance and to three phonon modes. We discuss the expected form of the effective Lagrangian and the phonon dispersion laws assuming the proposed crystal structure. Besides the interest for QCD and the related possible relevance to compact stars these considerations may become useful to atomic systems exhibiting crystalline superfluidity.

hep-ph↗
arXiv2001

Effective gluon interactions in the Colour Superconductive Phase of two flavor QCD

The gluon self-energies and dispersion laws in the color superconducting phase of QCD with two massless flavors are calculated using the effective theory near the Fermi surface. These quantities are calculated at zero temperature for all the eight gluons, those of the remaining SU(2) color group and those corresponding to the broken generators. The construction of the effective interaction is completed with the one loop calculation of the three- and four-point gluon interactions.

hep-ph↗
arXiv2001

Dispersion Laws for In-medium Fermions and Gluons in the CFL Phase of QCD

We evaluate several quantities appearing in the effective lagrangian for the color-flavor locked phase of high density QCD using a formalism which exploits the approximate decoupling of fermions with energy negative with respect to the Fermi energy. The effective theory is essentially two-dimensional and exhibits a Fermi velocity superselection rule, similar to the one found in the Heavy Quark Effective Theory. Within the formalism we reproduce, using gradient expansion, the results for the effective parameters of the Nambu-Goldstone bosons. We also determine the dispersion laws for the gluons. By coupling the theory to fermions and integrating over the two-dimensional degrees of freedom we obtain the effective description of in-medium fermions.

hep-ph↗
arXiv2001

Effective Field Theory for the Crystalline Colour Superconductive Phase of QCD

We present an effective field theory for high density, low temperature QCD in the crystalline colour superconductive phase (LOFF phase). This interesting phase of QCD is characterized by a gap parameter with a crystalline pattern, breaking traslational and rotational invariance, and could have astrophysical applications. In the effective theory the fermions have a Majorana mass, which, besides colour, breaks translation and rotation symmetries. Fermions couple to the three phonons arising from the breaking of rotation and translation invariance. Integrating out the fermions leads eventually to an effective lagrangian in terms of the phonon fields only, which satisfies an anisotropic dispersion relation.

hep-ph↗
arXiv2000

The s-sbar and K-Kbar nature of f_0(980) in D_s decays

We examine the D_s -> f_0(980) pi amplitude through a constituent quark-meson model, incorporating heavy quark and chiral symmetries, finding a good agreement with the recent E791 data analysis of D_s -> 3pi via f_0(980). The f_0(980) resonance is considered at the moment of production as an s sbar state, later evolving to a superposition of mainly s sbar and K Kbar. The analysis is also extended to the more frequent process D_s -> phi pi.

hep-ph↗
arXiv2000

Chiral Meson Masses at Finite Temperature and Density

The ratio of the sigma mass to the pion mass at finite temperatures and densities provides for a quantitative signal of chiral symmetry breaking. We calculate this ratio by using an extension to finite chemical potential of the field theoretic composite operator formalism as applied to QCD. The calculation is limited to regions of the phase diagram where only quark-antiquark condensates dominate (no quark-quark condensates) and it confirms the expected behaviours. In particular the sigma becomes an essentially stable particle in a narrow region bordering the transition line from broken to restored chirality . This pattern is qualitatively the same both for the region where the transition is of second order as for the region where it is of first order (apart from the discontinuities expected in the latter case).

hep-ph↗
arXiv2000

Predicting D -> sigma pi

We examine the D -> sigma pi amplitude through a constituent quark-meson model, incorporating heavy quark and chiral symmetries, finding a good agreement with the recent E791 data analysis of D -> 3 pi via sigma.

hep-ph↗
arXiv2000

B and B_s decays into three pseudoscalar mesons and the determination of the angle gamma of the unitarity triangle

We reconsider two classical proposals for the determination of the angle gamma of the unitarity triangle: B^\pm => chi_{c0} π^\pm => π^+π^-π^\pm and B_s => rho^0 K_S => π^+ π^- K_S. We point out the relevance, in both cases, of non resonant amplitudes, where the π^+ π^- pair is produced by weak decay of a B^* (J^P=1^-) or B_0 (J^P=0^+) off-shell meson. In particular, for the B decay channel, the inclusion of the B_0 pole completes some previous analyses and confirms their conclusions, provided a suitable cut in the Dalitz plot is performed; for the B_s decay the inclusion of the B^*, B_0 amplitudes enhances the role of the tree diagrams as compared to penguin amplitudes, which makes the theoretical uncertainty related to the B_s => rho^0 K_S decay process less significant. While the first method is affected by theoretical uncertainties, the second one is cleaner, but its usefulness will depend on the available number of events to perform the analysis.

hep-ph↗
arXiv2000

Measuring B -> rho pi decays and the unitarity angle alpha

The decay mode B -> rho pi is currently studied as a channel allowing, in principle, to measure without ambiguities the angle alpha of the unitarity triangle. It is also investigated by the CLEO Collaboration where a branching ratio larger than expected for the decay mode B+/- -> rho0 pi+/- has been found. We investigate the role that the B* and B(0+) resonances play in these analyses.

hep-ph↗
arXiv1999

The Lightest Pseudo-Goldstone Boson at Future e+e- Colliders

In a class of models of dynamical symmetry breaking not ruled out by the available data, the lightest neutral pseudo-Nambu-Goldstone boson P0 contains only down-type techniquarks and charged technileptons. Its mass scale is naturally determined by the b-quark and therefore it is likely to be light. As the presence of pseudo-Nambu-Goldstone bosons in models of dynamical symmetry breaking is a quite general feature, the search of the P0 at colliders is an interesting opportunity of putting limits on or discovering a dynamical electroweak symmetry breaking scenario. In this note we discuss the prospects for discovering and studying the P0 at future e+e- and gamma-gamma colliders.

hep-ph↗