arXiv subjects

F. Giannuzzi

Publications and source records attributed to F. Giannuzzi.

11 recordsLinked to original sources

arXiv2017

Investigating thermalization of a strongly interacting non-Abelian plasma

Using gauge/gravity duality methods, we study the relaxation towards equilibrium of strongly interacting non-Abelian matter. We adopt boundary sourcing to drive the system out-of-equilibrium, and analyze the equilibration process through local probes (energy density and pressures) and nonlocal probes (lengths of the geodesics between two boundary points and extremal surfaces having a Wilson loop as contour on the boundary). We also investigate the real-time dissociation of the heavy quarkonium in the out-of-equilibrium plasma. Systematic comparison with the results of a geometry dual to viscous hydrodynamics sheds light on the thermalization process.

hep-ph↗

arXiv2017

Quarkonium dissociation in a far-from-equilibrium holographic setup

The real-time dissociation of the heavy quarkonium in a strongly coupled boost-invariant non-Abelian plasma relaxing towards equilibrium is analyzed in a holographic framework. The effects driving the plasma out of equilibrium are described by boundary quenching, impulsive variations of the boundary metric. Quarkonium is represented by a classical string with endpoints kept close to the boundary. The evolution of the string profile is computed in the time-dependent geometry, and the dissociation time is evaluated for different configurations with respect to the direction of the plasma expansion. Dissociation occurs fastly for the quarkonium placed in the transverse plane.

hep-ph↗

arXiv2015

Holographic Oddballs

The spectrum of the glueball with $J^{PC}=0^{--}$ is computed using different bottom-up holographic models of QCD. The results indicate a lowest-lying state lighter than in the determination by other methods, with mass $m \simeq 2.8$ GeV. The in-medium properties of this gluonium are investigated, and stability against thermal and density effects is compared to other hadronic systems. Production and decay modes are identified, useful for searching the $J^{PC}=0^{--}$ glueball.

hep-ph↗

arXiv2015

On thermalization of a boost-invariant non Abelian plasma

Using a holographic method, we further investigate the relaxation towards the hydrodynamic regime of a boost-invariant non-Abelian plasma taken out-of-equilibrium. In the dual description, the system is driven out-of-equilibrium by boundary sourcing, a deformation of the boundary metric, as proposed by Chesler and Yaffe. The effects of several deformation profiles on the bulk geometry are investigated by the analysis of the corresponding solutions of the Einstein equations. The time of restoration of the hydrodynamic regime is investigated: setting the effective temperature of the system at the end of the boundary quenching to $T_{eff}(τ^*)=500$ MeV, the hydrodynamic regime is reached after a lapse of time of ${\cal O}$(1 fm/c).

hep-ph↗

arXiv2012

New meson spectroscopy with open charm and beauty

All the available experimental information on open charm and beauty mesons is used to classify the observed states in heavy quark doublets. The masses of some of the still unobserved states are predicted, in particular in the beauty sector. Adopting an effective Lagrangian approach based on the heavy quark and chiral symmetry, individual decay rates and ratios of branching fractions are computed, with results useful to assign the quantum numbers to recently observed charmed states which still need to be properly classified. Implications and predictions for the corresponding beauty mesons are provided. The experimental results are already copious, and are expected to grow up thanks to the experiments at the LHC and to the future high-luminosity flavour and $p-\bar p$ facilities.

hep-ph↗

arXiv2012

Anomalous $AV^*V$ vertex function in the soft-wall holographic model of QCD

We consider the vertex function of two vector and one axial-vector currents using the soft-wall holographic model of QCD with the Chern-Simons term. Two structure functions $w_L$ and $w_T$ describe such a vertex in the special case in which one of the two vector currents corresponds to an on-shell soft photon. We briefly review the QCD results for these functions, obtained from triangular loop diagrams with quarks having mass $m_q=0$ or $m_q \neq 0$, we compute $w_L$ and $w_T$ in the soft-wall model and compare the outcome to the QCD findings. We also calculate and discuss the two-point $Π_{VV}-Π_{AA}$ correlation function, together with a few low-energy constants, which turn out to be close to the QCD results.

hep-ph↗

arXiv2011

Off-shell effects for t-channel and s-channel single-top production at NLO in QCD

In this work we present a calculation of both t-channel and s-channel single-top production at next-to-leading order in QCD for the Tevatron and for the LHC at a centre-of-mass energy of 7 TeV. All the cross sections and kinematical distributions presented include leading non-factorizable corrections arising from interferences of the production and decay subprocesses, extending previous results beyond the narrow-width approximation. The new off-shell effects are found to be generally small, but can be sizeable close to kinematical end-points and for specific distributions.

hep-ph↗

arXiv2009

Holographic Approach to Finite Temperature QCD: The Case of Scalar Glueballs and Scalar Mesons

We study scalar glueballs and scalar mesons at $T \neq 0$ in the soft wall holographic QCD model. We find that, using the Anti-de Sitter-Black Hole metric for all values of the temperature, the masses of the hadronic states decrease and the widths become broader when T increases, and there are temperatures for which the states disappear from the scalar glueball and scalar meson spectral functions. However, the values of the temperatures in correspondence of which such phenomena occur are low, of the order of 40-60 MeV. A consistent holographic description of in-medium effects on hadron properties should include the Hawking-Page transition, which separates the phase with the Anti-de Sitter metric at small temperatures from the phase with Anti-de Sitter-Black Hole metric at high temperatures.

hep-ph↗

arXiv2008

Phase diagram of a generalized Winfree model

We study the phase diagram of a generalized Winfree model. The modification is such that the coupling depends on the fraction of synchronized oscillators, a situation which has been noted in some experiments on coupled Josephson junctions and mechanical systems. We let the global coupling k be a function of the Kuramoto order parameter r through an exponent z such that z=1 corresponds to the standard Winfree model, z<1 strengthens the coupling at low r (low amount of synchronization) and, at z>1, the coupling is weakened for low r. Using both analytical and numerical approaches, we find that z controls the size of the incoherent phase region, and one may make the incoherent behavior less typical by choosing z<1. We also find that the original Winfree model is a rather special case, indeed the partial locked behavior disappears for z>1. At fixed k and varying gamma, the stability boundary of the locked phase corresponds to a transition that is continuous for z<1 and first-order for z>1. This change in the nature of the transition is in accordance with a previous study on a similarly modified Kuramoto model.

cond-mat.dis-nn↗

arXiv2008

AdS-QCD quark-antiquark potential, meson spectrum and tetraquarks

AdS/QCD correspondence predicts the structure of quark-antiquark potential in the static limit. We use this piece of information together with the Salpeter equation (Schrödinger equation with relativistic kinematics) and a short range hyperfine splitting potential to determine quark masses and the quark potential parameters from the meson spectrum. The agreement between theory and experimental data is satisfactory provided one considers only mesons comprising at least one heavy quark. We use the same potential (in the one-gluon-exchange approximation) and these data to estimate constituent diquark masses. Using these results as an input we compute tetraquark masses using a diquark-antidiquark model. The masses of the states X(3872) or Y(3940) are predicted rather accurately. We also compute tetraquark masses with open charm and strangeness. Our result is that tetraquark candidates such as D_s(2317), D_s(2457) or X(2632) can hardly be interpreted as diquark-antidiquark states within the present approach.

hep-ph↗

arXiv2008

Light scalar mesons in the soft-wall model of AdS/QCD

We study light scalar mesons in the AdS/QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators in AdS and QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: this discrepancy is related to the description of chiral symmetry breaking in this model.

hep-ph↗