Searcharxiv⌕ Search

arXiv subjects

R. Casalbuoni

Publications and source records attributed to R. Casalbuoni.

At least 19 recordsLinked to original sources
arXiv2015

The Extended Bess Model: Bounds from Precision Electroweak Measurements

We present an effective Lagrangian parameterization describing scalar, vector, and axial-vector bound states, originating from a strong breaking of the electroweak symmetry, based on the global symmetry $SU(N)_L\otimes SU(N)_R$. In this approach vector and axial-vector bound states are gauge bosons associated to a hidden $SU(N)_L\otimes SU(N)_R$ symmetry. After the gauging of the electroweak symmetry, the corrections to the self-energies of the standard model gauge bosons are calculated and bounds on the parameter space of the model arising from precision measurements are studied. The self-energy corrections arise from spin 1 mixings, pseudogoldstones loops, pseudogoldstone-spin 1 loops, and tadpole terms. The one-loop terms tend to decrease both isospin conserving and isospin violating corrections. Careful calculation for standard $SU(8)$ QCD-scaled technicolor shows that strictly this model (which has however serious theoretical difficulties on his own) is still marginally allowed at present experimental precision.

hep-ph↗
arXiv2008

A linear moose model with pairs of degenerate gauge boson triplets

The possibility of the existence of a strongly interacting electroweak symmetry breaking sector, as opposed to the weakly interacting light Higgs of the Standard Model, is not yet ruled out by experiments. In this paper we make an extensive study of a deconstructed model (or ``moose'' model) providing a possible effective description of such a strong symmetry breaking sector, and show its compatibility with experimental data for a wide portion of the model parameters space. The model is a direct generalization of the previously proposed D-BESS model.

hep-ph↗
arXiv2007

Holographic approach to a minimal Higgsless model

In this work, following an holographic approach, we carry out a low energy effective study of a minimal Higgsless model based on SU(2) bulk symmetry broken by boundary conditions, both in flat and warped metric. The holographic procedure turns out to be an useful computation technique to achieve an effective four dimensional formulation of the model taking into account the corrections coming from the extra dimensional sector. This technique is used to compute both oblique and direct contributions to the electroweak parameters in presence of fermions delocalized along the fifth dimension.

hep-ph↗
arXiv2006

Effective fermion couplings in warped 5D Higgsless theories

We consider a five dimensional SU(2) gauge theory with fermions in the bulk and with additional SU(2) and U(1) kinetic terms on the branes. The electroweak breaking is obtained by boundary conditions. After deconstruction, fermions in the bulk are eliminated by using their equations of motion. In this way Standard Model fermion mass terms and direct couplings to the internal gauge bosons of the moose are generated. The presence of these new couplings gives a new contribution to the epsilon_3 parameter in addition to the gauge boson term. This allows the possibility of a cancellation between the two contributions, which can be local (site by site) or global. Going back to the continuum, we show that the implementation of local cancellation in any generic warped metric leaves massless fermions. This is due to the presence of one horizon on the infrared brane. However we can require a global cancellation of the new physics contributions to the epsilon_3 parameter. This fixes relations among the warp factor and the parameters of the fermion and gauge sectors.

hep-ph↗
arXiv2006

Influence of finite quark chemical potentials on the three flavor LOFF phase of QCD

We study in the Ginzburg-Landau approximation, the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors and one plane wave, including terms of order O(1/mu). We show that the LOFF window is slightly enlarged, and actually splits into two different regions, one characterized by u-s and d-u pairings and the other with d-u pairs only.

hep-ph↗
arXiv2006

Ginzburg-Landau approach to the three flavor LOFF phase of QCD

We explore, using a Ginzburg-Landau expansion of the free energy, the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors, using the NJL four-fermion coupling to mimic gluon interactions. We find that, below the point where the QCD homogeneous superconductive phases should give way to the normal phase, Cooper condensation of the pairs u-s and d-u is possible, but in the form of the inhomogeneous LOFF pairing.

hep-ph↗
arXiv2005

Deconstructed Higgsless Models

We consider the possibility of constructing realistic Higgsless models within the context of deconstructed or moose models. We show that the constraints coming from the electro-weak esperimental data are very severe and that it is very difficult to reconcile them with the requirement of improving the unitarity bound of the Higgsless Standard Model. On the other hand, with some fine tuning, a solution is found by delocalizing the standard fermions along the lattice line, that is allowing the fermions to couple to the moose gauge fields.

hep-ph↗
arXiv2005

A NJL-based study of the QCD critical line

We employ a 3 flavor NJL model to stress some general remarks about the QCD critical line. The dependence of the critical curve on $μ_q=(μ_u+μ_d)/2$ and $μ_I=(μ_u-μ_d)/2$ is discussed. The quark masses are varied to confirm that, in agreement with universality arguments, the order of transition depends on the number of active flavors $N_f$. The slope of the critical curve vs. chemical potential is studied as a function of $N_f$. We compare our results with those recently obtained in lattice simulations to establish a comparison among different models.

hep-ph↗
arXiv2005

Meissner masses in the gCFL phase of QCD

We calculate the Meissner masses of gluons in neutral three-flavor color superconducting matter for finite strange quark mass. In the CFL phase the eissner masses are slowly varying function of the strange quark mass. For large strange quark mass, in the so called gCFL phase, the Meissner masses of gluons with colors $a=1,2,3$ and 8 become imaginary, indicating an instability.

hep-ph↗
arXiv2005

Playing with fermion couplings in Higgsless models

We discuss the fermion couplings in a four dimensional SU(2) linear moose model by allowing for direct couplings between the left-handed fermions on the boundary and the gauge fields in the internal sites. This is realized by means of a product of non linear $σ$-model scalar fields which, in the continuum limit, is equivalent to a Wilson line. The effect of these new non local couplings is a contribution to the $ε_3$ parameter which can be of opposite sign with respect to the one coming from the gauge fields along the string. Therefore, with some fine tuning, it is possible to satisfy the constraints from the electroweak data.

hep-ph↗
arXiv2004

Pion and kaon condensation in a 3-flavor NJL model

We analyze the phase diagram of a three-flavor Nambu-Jona-Lasinio model at finite temperature $T$ and chemical potentials $μ_u, μ_d, μ_s$. We study the competition of pion and kaon condensation and we propose a physical situation in which kaon condensation could be led only by light quark finite densities.

hep-ph↗
arXiv2004

Skyrmions and pentaquarks in the quark-hadron continuity perspective

We argue that in the color-flavor-locking (CFL) superconducting phase classical soliton solutions can exist, whose excitations should be interpreted as states formed by a quark (or an antiquark) and condensed diquarks. This finding extends the picture of quark-hadron-continuity showing the existence of a region, intermediate between the CFL and the hypernuclear phase, where chiral solitons and Nambu Goldstone bosons can exist. We derive an expression of the soliton mass in terms of the QCD coupling, $g_s$, and the Nambu Goldstone boson parameters. From the quark-hadron continuity we can draw an argument in favor of the interpretation of the $Θ^+(1540)$ particle in terms of a strange antiquark and two highly correlated $ud$ pairs (diquarks).

hep-ph↗
arXiv2004

Magnetic properties of the Larkin-Ovchinnikov-Fulde-Ferrell superconducting phase

We compute, at the first order in the fine structure constant, the parameters of the electromagnetic Lagrangian for the inhomogeneous Larkin-Ovchinnikov-Fulde-Ferrell phase in Quantum Chromodynamics (QCD) and in condensed matter. In particular we compute for QCD with two flavors the dielectric and the magnetic permeability tensors, and for condensed matter superconductors the penetration depth of external magnetic fields.

hep-ph↗
arXiv2004

Moose models with vanishing $S$ parameter

In the linear moose framework, which naturally emerges in deconstruction models, we show that there is a unique solution for the vanishing of the $S$ parameter at the lowest order in the weak interactions. We consider an effective gauge theory based on $K$ SU(2) gauge groups, $K+1$ chiral fields and electroweak groups $SU(2)_L$ and $U(1)_Y$ at the ends of the chain of the moose. $S$ vanishes when a link in the moose chain is cut. As a consequence one has to introduce a dynamical non local field connecting the two ends of the moose. Then the model acquires an additional custodial symmetry which protects this result. We examine also the possibility of a strong suppression of $S$ through an exponential behavior of the link couplings as suggested by Randall Sundrum metric.

hep-ph↗
arXiv2004

Effective Gap Equation for the Inhomogeneous LOFF Superconductive Phase

We present an approximate gap equation for different crystalline structures of the LOFF phase of high density QCD at T=0. This equation is derived by using an effective condensate term obtained by averaging the inhomogeneous condensate over distances of the order of the crystal lattice size. The approximation is expected to work better far off any second order phase transition. As a function of the difference of the chemical potentials of the up and down quarks, $δμ$, we get that the octahedron is energetically favored from $δμ=Δ_0/\sqrt 2$ to $0.95Δ_0$, where $Δ_0$ is the gap for the homogeneous phase, while in the range $0.95Δ_0-1.32Δ_0$ the face centered cube prevails. At $δμ=1.32Δ_0$ a first order phase transition to the normal phase occurs.

hep-ph↗