Searcharxiv⌕ Search

arXiv subjects

Francesco Sannino

Publications and source records attributed to Francesco Sannino.

303 records · Page 17Linked to original sources
arXiv2001

Relativistic Massive Vector Condensation

At sufficiently high chemical potential massive relativistic spin one fields condense. This phenomenon leads to the spontaneous breaking of rotational invariance while linking it to the breaking of internal symmetries. We study the relevant features of the phase transition and the properties of the generated Goldstone excitations. The interplay between the internal symmetry of the vector fields and their Lorentz properties is studied. We predict that new phases set in when vectors condense in Quantum Chromodynamics like theories.

hep-ph↗
arXiv2001

Supernovae, Hypernovae and Color Superconductivity

We argue that Color Superconductivity (CSC, Cooper pairing in quark matter leading to the breaking of SU(3) color symmetry) may play a role in triggering the explosive endpoint of stellar evolution in massive stars (M > 8 M_{\odot}). We show that the binding energy release in the transition of a sub-core region to the CSC phase can be of the same order of magnitude as the gravitational binding energy release from core collapse. The core temperature during collapse is likely below the critical temperature for CSC, and the transition is first order, proceeding on Fermi timescales when the pressure reaches a critical value of several times nuclear density. We also discuss the implications for hypernova events with total ejecta energy of 10-100 times that of type II supernova.

hep-ph↗
arXiv1999

Enhanced Global Symmetries and a Strong Electroweak Sector

In this talk I review the intriguing possibility (see Reference[1]) that the physical spectrum of a vector-like gauge field theory exhibits an enhanced global symmetry near a chiral phase transition. A transition from the Goldstone phase to the symmetric phase is expected as the number of fermions Nf is increased to some critical value. Various investigations have suggested that a parity-doubled spectrum develops as the critical value is approached. Using an effective Lagrangian as a guide one observes that a parity doubling is associated with the appearance of an enhanced global symmetry in the spectrum of the theory. If such a near-critical theory describes symmetry breaking in the electroweak theory, the additional symmetry suppresses the contribution of the parity doubled sector to the S parameter.

hep-ph↗
arXiv1999

Chiral Phase Transition for SU(N) Gauge Theories

We describe the chiral phase transition for vector-like SU(N) gauge theories as a function of the number of quark flavors Nf by making use of an anomaly-induced effective potential. The potential depends explicitly on the full beta-function and the anomalous dimension γof the quark mass operator. By using this potential we argue that chiral symmetry is restored for γ<1. A perturbative computation of γthen leads to an estimate of the critical value Nf^c for the transition.

hep-ph↗
arXiv1998

Putative Light Scalar Nonet

We investigate the "family" relationship of a possible scalar nonet composed of the a_0(980), the f_0(980) and the σand κtype states found in recent treatments of ππand πK scattering. We work in the effective Lagrangian framework, starting from terms which yield "ideal mixing" according to Okubo's original formulation. It is noted that there is another solution corresponding to dual ideal mixing which agrees with Jaffe's picture of scalars as qq\bar q \bar q states rather than as q\bar q states. At the Lagrangian level there is no difference in the formulation of the two cases (other than the numerical values of the coefficients). In order to agree with experiment, additional mass and coupling terms which break ideal mixing are included. The resulting model turns out to be closer to dual ideal mixing than to conventional ideal mixing; the scalar mixing angle is roughly -17 degrees in a convention where dual ideal mixing is 0 degrees.

hep-ph↗
arXiv1998

From Super QCD to QCD

We present a ``toy'' model for breaking supersymmetric gauge theories at the effective Lagrangian level. We show that it is possible to achieve the decoupling of gluinos and squarks, below a given supersymmetry breaking scale m, in the fundamental theory for super QCD once a suitable choice of supersymmetry breaking terms is made. A key feature of the model is the description of the ordinary QCD degrees of freedom via the auxiliary fields of the supersymmetric effective Lagrangian. Once the anomaly induced effective QCD meson potential is deduced we also suggest a decoupling procedure, when a flavored quark becomes massive, which mimics the one employed by Seiberg for supersymmetric theories. It is seen that, after quark decoupling, the QCD potential naturally converts to the one with one less flavor. Finally we investigate the N_c and N_f dependence of the η^{\prime} mass.

hep-th↗
arXiv1998

Towards Deriving Higgs Lagrangian from Gauge Theories

A new method of deriving the Higgs Lagrangian from vector-like gauge theories is explored. After performing a supersymmetric extension of gauge theories we identify the auxiliary field associated with the "meson" superfield, in the low energy effective theory, as the composite Higgs field. The auxiliary field, at tree level, has a "negative squared mass". By computing the one-loop effective action in the low energy effective theory, we show that a kinetic term for the auxiliary field emerges when an explicit non-perturbative mechanism for supersymmetry breaking is introduced. We find that, due to the naive choice of the Kaehler potential, the Higgs potential remains unbounded from the below. A possible scenario for solving this problem is presented. It is also shown that once chiral symmetry is spontaneously broken via a non-zero vacuum expectation value of the Higgs field, the low energy composite fermion field acquires a mass and decouples, while in the supersymmetric limit it was kept massless by the 't Hooft anomaly matching conditions.

hep-th↗
arXiv1997

Effective Lagrangian Models for Gauge Theories of Fundamental Interactions

In this thesis we show that the effective Lagrangian models, encoding the relevant symmetries of the underlying fundamental gauge theory for strong interactions (QCD), provide a reasonable understanding of the interactions among Light Mesons at intermediate energies as well as of the properties of Heavy Baryons.

hep-ph↗
arXiv1997

Toy Model for Breaking Super Gauge Theories at the Effective Lagrangian Level

We propose a toy model to illustrate how the effective Lagrangian for super QCD might go over to the one for ordinary QCD by a mechanism whereby the gluinos and squarks in the fundamental theory decouple below a given supersymmetry breaking scale $m$. The implementation of this approach involves a suitable choice of possible supersymmetry breaking terms. An amusing feature of the model is the emergence of the ordinary QCD degrees of freedom which were hidden in the auxiliary fields of the supersymmetric effective Lagrangian.

hep-th↗
arXiv1997

Generalization of the Bound State Model

In the bound state approach the heavy baryons are constructed by binding, with any orbital angular momentum, the heavy meson multiplet to the nucleon considered as a soliton in an effective meson theory. We point out that this picture misses an entire family of states, labeled by a different angular momentum quantum number, which are expected to exist according to the geometry of the three-body constituent quark model (for N_C=3). To solve this problem we propose that the bound state model be generalized to include orbitally excited heavy mesons bound to the nucleon. In this approach the missing angular momentum is ``locked-up'' in the excited heavy mesons. In the simplest dynamical realization of the picture we give conditions on a set of coupling constants for the binding of the missing heavy baryons of arbitrary spin. The simplifications made include working in the large M limit, neglecting nucleon recoil corrections, neglecting mass differences among different heavy spin multiplets and also neglecting the effects of light vector mesons.

hep-ph↗
arXiv1996

Hidden Structure in a Lagrangian for Hyperfine Splitting of the Heavy Baryons

We investigate the hyperfine splitting of the heavy baryons in the bound-state approach. We start with an ordinary relativistic Lagrangian which has been extensively used to discuss finite mass corrections to the heavy limit predictions. It turns out that the dominant contribution arises from terms which do not manifestly break the heavy spin symmetry. The actual heavy spin violating terms are uncovered by carefully performing a 1/M expansion of this Lagrangian.

hep-ph↗
arXiv1995

Simple Description of Pion-Pion Scattering to 1 GeV

Motivated by the 1/Nc expansion, we present a simple model of pion-pion scattering as a sum of a `current-algebra' contact term and resonant pole exchanges. The model preserves crossing symmetry as well as unitarity up to 1.2 GeV. Key features include chiral dynamics, vector meson dominance, a broad low energy scalar (sigma) meson and a `Ramsauer-Townsend' mechanism for the understanding of the 980 MeV region. We discuss in detail the `regularization' (corresponding to rescattering effects) necessary to make all these nice features work.

hep-ph↗
arXiv1993

Violation Of The $ΔI = 1/2$ Rule In $D \to ππ$ Decays

A strong violation of the $\displaystyle{ΔI = {1\over 2}} $ rule has experimentally been found in the $\displaystyle{D \to ππ}$ decays [1]. In this letter we will show that the order of magnitude of this violation can be understood in terms of the pure quantum chromo dynamics corrections to the weak interactions.

hep-ph↗