arXiv subjects

G. Nardulli

Publications and source records attributed to G. Nardulli.

At least 55 records · Page 3Linked to original sources

arXiv2002

Jet analysis by Deterministic Annealing

We perform a comparison of two jet clusterization algorithms. The first one is the standard Durham algorithm and the second one is a global optimization scheme, Deterministic Annealing, often used in clusterization problems, and adapted to the problem of jet identification in particle production by high energy collisions; in particular we study hadronic jets in WW production by high energy electron positron scattering. Our results are as follows. First, we find that the two procedures give basically the same output as far as the particle clusterization is concerned. Second, we find that the increase of CPU time with the particle multiplicity is much faster for the Durham jet clustering algorithm in comparison with Deterministic Annealing. Since this result follows from the higher computational complexity of the Durham scheme, it should not depend on the particular process studied here and might be significant for jet physics at LHC as well.

hep-ph↗

arXiv2002

Effective Fields in Dense Quantum Chromodynamics

In the high density, low temperature limit, Quantum Chromodynamics exhibits a transition to phases characterized by color superconductivity and energy gaps in the fermion spectra. We review some fundamental results obtained in this area and in particular we describe the low energy effective lagrangian describing the motion of the quasi-particles in the high density medium (High Density Effective Theory).

hep-ph↗

arXiv2002

Charming penguin contributions to charmless B decays into two pseudoscalar mesons

We present estimates of the charming penguin contribution to B => K pi, pi pi,K eta, K eta' decays due to intermediate charmed meson states. We find that this contribution is indeed significant for B => K pi decays, and its inclusion, together with the tree and penguin terms, produces large branching ratios in agreement with data, though the analysis is affected by large theoretical uncertainties. On the other hand, for B => pi pi, K eta, K eta' decays, the effect of the charming penguin contribution is more modest. We also compute CP asymmetries for B => K pi, pi pi decays and we obtain rather large results.

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↗

arXiv2001

Charming penguin contributions to B => K π

We present calculations of the charming-penguin long-distance contributions to B => K πdecays due to intermediate charmed meson states. Our calculation is based on the Chiral Effective Lagrangean for light and heavy mesons, corrected for the hard pion and kaon momenta. We find that the charming-penguin contributions increase significantly the B => K πdecay rates in comparison with the short-distance contributions, giving results in better agreement with experimental data.

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

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

Controlling chaos in diluted networks with continuous neurons

Diluted neural networks with continuous neurons and nonmonotonic transfer function are studied, with both fixed and dynamic synapses. A noisy stimulus with periodic variance results in a mechanism for controlling chaos in neural systems with fixed synapses: a proper amount of external perturbation forces the system to behave periodically with the same period as the stimulus.

cond-mat.dis-nn↗

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↗

arXiv2000

B Meson Transitions into Higher Mass Charmed Resonances

We use QCD sum rules to estimate the universal form factors describing the semileptonic B decays into excited charmed resonances, such as the $1^-$ and $2^-$ states $D_1^{*}$ and $D_2^{*}$ belonging to the $s_\ell^P={3/2}^-$ heavy quark doublet, and the $2^-$ and $3^-$ states $D_2^{*\prime}$ and $D_3$ belonging to the $s_\ell^P={5\2}^-$ doublet.

hep-ph↗

arXiv1999

B => ππ\ell νdecays in a QCD relativistic potential model

In the framework of a QCD relativistic potential model we evaluate the form factors describing the exclusive decay B => ππ\ell ν. The calculation is performed in a phase space region far away from the resonances and therefore is complementary to other decay mechanisms where the pions are produced by intermediate particles, e.g. in the chiral approach. We give an estimate of the contribution of the non resonant channel of the order of BR(B- => π+ π- \ell ν) \approx 2.2 x 10^(-4).

hep-ph↗

arXiv1999

The semileptonic B->pi decay in a Constituent Quark-Meson model

We evaluate the form factors describing the exclusive decay B-> pi l nu by using a Constituent Quark-Meson model based on an effective quark-meson Lagrangian (CQM). The model allows for an expansion in the pion momenta and we consider terms up to the first order in the pion field derivatives. We compute the leading terms in the soft pion limit and consider corrections to this limit.

hep-ph↗

arXiv1999

Cottingham formula and the pion electromagnetic mass difference at finite temperature

We generalize the Cottingham formula at finite (T\neq 0) temperature by using the imaginary time formalism. The Cottingham formula gives the theoretical framework to compute the electromagnetic mass differences of the hadrons using a dispersion relation approach. It can be also used in other contexts, such as non leptonic weak decays, and its generalization to finite temperature might be useful in evaluating thermal effects in these processes. As an application we compute the π^+-π^0 mass difference at T\neq 0; at small T we reproduce the behaviour found by other authors: δm^2(T)= δm^2(0)+\mathcal{O}(αT^2), while for moderate T, near the deconfinement temperature, we observe deviations from this behaviour.

hep-ph↗

arXiv1999

Chaos in neural networks with a nonmonotonic transfer function

Time evolution of diluted neural networks with a nonmonotonic transfer function is analitically described by flow equations for macroscopic variables. The macroscopic dynamics shows a rich variety of behaviours: fixed-point, periodicity and chaos. We examine in detail the structure of the strange attractor and in particular we study the main features of the stable and unstable manifolds, the hyperbolicity of the attractor and the existence of homoclinic intersections. We also discuss the problem of the robustness of the chaos and we prove that in the present model chaotic behaviour is fragile (chaotic regions are densely intercalated with periodicity windows), according to a recently discussed conjecture. Finally we perform an analysis of the microscopic behaviour and in particular we examine the occurrence of damage spreading by studying the time evolution of two almost identical initial configurations. We show that for any choice of the parameters the two initial states remain microscopically distinct.

cond-mat.dis-nn↗

arXiv1999

Semileptonic and rare B meson decays into a light pseudoscalar meson

In the framework of a QCD relativistic potential model we evaluate the form factors describing the exclusive decays B => πl nu and B => K l+ l-. The present calculation extends a previous analysis of B meson decays into light vector mesons. We find results in agreement with the data, when available, and with the theoretical constraints imposed by the Callan-Treiman relation and the infinite heavy quark mass limit.

hep-ph↗