Searcharxiv⌕ Search

arXiv subjects

R. Casalbuoni

Publications and source records attributed to R. Casalbuoni.

At least 55 records · Page 3Linked to original sources
arXiv2000

Signals of the degenerate BESS model at the LHC

We discuss the possible signals of the degenerate BESS model at the LHC. This model describes a strongly interacting scenario responsible of the spontaneous breaking of the electroweak symmetry. It predicts two triplets of extra gauge bosons which are almost degenerate in mass. Due to this feature, the model has the property of decoupling and therefore, at low energies (below or of the order of $100 GeV$) it is nearly indistinguishable from the Standard Model. However the new resonances, both neutral and charged, should give quite spectacular signals at the LHC, where the c.o.m. energy will allow to produce these gauge bosons directly.

hep-ph↗
arXiv1999

Study of the anomalous couplings at NLC with polarized beams

The present contribution reports a study of the effects of anomalous gauge and fermionic couplings in the process $e^+e^- -> W^+W^-$ at the Next Linear Collider focusing in particular on the option of polarized beams. We conclude that polarized beams with adjustable degree of polarization would constitute a very significant tool in the search for new physics.

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↗
arXiv1999

Pseudoscalar Masses in the Effective Theory for Color-Flavor Locking in high density QCD

The constants of the effective action describing the massless modes in the color-flavor-locking phase of QCD have been recently evaluated at high density. Values of the pseudoscalar masses for nonvanishing quark masses have also been given. The calculated values show however a puzzling feature: when $m_u=m_d=0$ and $m_s\not=0$ all the goldstones remain massless. We show that an additional invariant is present which avoids this feature. We costruct this invariant and discuss the emerging mass pattern for the pseudogoldstones. This provides for a complete scheme for the pseudogoldstone masses in the color-flavor-locking phase of QCD.

hep-ph↗
arXiv1999

The Color-Flavor Locking Phase at T \not =0$

We study the color-flavor locked phase of QCD with three massless quarks at high chemical potential and small non zero temperatures. We make use of the recently introduced effective action to describe such a phase. We obtain the exact order T^2 behaviour of the condensates and of the pressure by formally comparing the derivative from the QCD functional with symmetry breaking to that from the effective lagrangian with external sources, respecting the residual Z_2 invariance of the color-flavor locked phase. From these exact results, but now at a very tentative level of conjecture, we are lead to think that the phase structure of QCD at very high density consists of two superconducting phases and a symmetric one.

hep-ph↗
arXiv1999

Effective Theory for Color-Flavor Locking in high Density QCD

We describe the low energy excitations of the diquark condensates in the color-flavor locked phase of QCD with three massless flavors, at high baryon densities, in terms of a non-linear effective lagrangian. Such a lagrangian is formally seen to correspond to the lagrangian for the hidden gauge symmetry description of the effective low energy chiral lagrangian, the role of the hidden symmetry being played by color. In particular, this agrees with the conjecture that the light degrees of freedom of the two phases are in correspondence to each other (complementarity). The discussion includes consideration of the breaking of Lorentz invariance in presence of matter density.

hep-ph↗
arXiv1999

SM Kaluza-Klein Excitations and Electroweak Precision Tests

We consider a minimal extension to higher dimensions of the Standard Model, having one compactified dimension, and we study its experimental tests in terms of electroweak data. We discuss tests from high-energy data at the $Z$-pole, and low-energy tests, notably from atomic parity violation data. This measurement combined with neutrino scattering data strongly restricts the allowed region of the model parameters. Furthermore this region is incompatible at 95% CL with the restrictions from high-energy experiments. Of course a global fit to all data is possible but the $χ^2_{\rm min}$ for degree of freedom is unpleasantly large.

hep-ph↗
arXiv1999

Detecting and Studying the Lightest Pseudo-Goldstone Boson at Future $pp$, $e^+e^-$ and $μ^+μ^-$ Colliders

For an attractive class of dynamical symmetry breaking (technicolor) models, the lightest neutral pseudo-Nambu-Goldstone boson ($\pzero$) contains only down-type techniquarks and charged technileptons. We discuss the prospects for discovering and studying the $\pzero$ of such models at the Tevatron and the LHC and at future $\epem$ and $\mupmum$ colliders. Depending upon the number of technicolors, $\ntc$, discovery of the $\pzero$ at the Tevatron and the LHC in the $gg\to\pzero\to\gam\gam$ mode could be possible over a wide range of mass. For $\ntc=4$, discovery of the $\pzero$ at an $\epem$ collider via the reaction $\epem\to\gam \pzero$ should be possible as long as $\mpzero$ is not near $\mz$. In the $\gam\gam$ collider mode of operation at an $\epem$ collider, the $\gam\gam\to\pzero\to b\anti b$ signal should be very robust if $\ntc=4$. For the minimal $\ntc=1$ case, detection of the $\pzero$ at the Tevatron and in $\epem$ collisions will be very difficult, and the precision of measurements at the LHC and the $\gam\gam$ collider decline markedly. A $\mupmum$ collider yields a $\pzero$ production rate that does not depend markedly upon $\ntc$. At a $\mupmum$ collider discovery of the $\pzero$ as an $s$-channel resonance should prove possible via scanning, even if it has not already been detected elsewhere. Once $\mpzero$ is precisely known, operation of the $\mupmum$ collider as a $\pzero$ factory will allow precision measurements of enough observables to determine the number of technicolors of the theory and (up to a discrete set of ambiguities) the fundamental parameters of the low-energy effective Lagrangian describing the Yukawa couplings of the $\pzero$.

hep-ph↗
arXiv1999

Bounds on New Physics from the New Data on Parity Violation in Atomic Cesium

We assume the latest experimental determination of the weak charge of atomic cesium and analyze its implications for possible new physics. We notice that the data would imply positive upper and lower bounds on the new physics contribution to the weak charge, $δ_NQ_W$. The required new physics should be of a type not severely constrained by the high energy precision data. A simplest possibility would be new neutral vector bosons almost un-mixed to the $Z$ and with sizeable couplings to fermions. The lower positive bound would however forbid zero or negative $δ_NQ_W$ and exclude not only the standard model but also models with sequential $Z^\prime$, in particular simple-minded towers of $Z$-like excitations from extra-dimensions. The bound would also imply an upper limit on the $Z^\prime$ mass within the models allowed. Conclusions are also derived for models of four-fermion contact interactions.

hep-ph↗
arXiv1999

Analysis of Narrow s-channel Resonances at Lepton Colliders

The procedures for studying a single narrow s-channel resonance or nearly degenerate resonances at a lepton collider, especially a muon collider, are discussed. In particular, we examine four methods for determining the parameters of a narrow s-channel resonance: scanning the resonance, measuring the convoluted cross section, measuring the Breit-Wigner area, and sitting on the resonance while varying the beam energy resolution. This latter procedure is new and appears to be potentially very powerful. Our focus is on computing the errors in resonance parameters resulting from uncertainty in the beam energy spread. Means for minimizing these errors are discussed. The discussion is applied to the examples of a light SM-Higgs, of the lightest pseudogoldstone boson of strong electroweak breaking, and of the two spin-1 resonances of the Degenerate BESS model (assuming that the beam energy spread is less than their mass splitting). We also examine the most effective procedures for nearly degenerate resonances, and apply these to the case of Degenerate BESS resonances with mass splitting of order the beam energy spread.

hep-ph↗
arXiv1999

A New Technique for Determining the Properties of a Narrow $s$-channel Resonance at a Muon Collider

We explore an alternative to the usual procedure of scanning for determining the properties of a narrow $s$-channel resonance. By varying the beam energy resolution while sitting on the resonance peak, the width and branching ratios of the resonance can be determined. The statistical accuracy achieved is superior to that of the usual scan procedure in the case of a light SM-like Higgs boson with $\mh>130\gev$ or for the lightest pseudogoldstone boson of a strong electroweak breaking model if $\mpzero>150\gev$.

hep-ph↗
arXiv1998

Pseudoscalar and scalar meson masses at finite temperature

The composite operator formalism is applied to QCD at finite temperature to calculate the masses of scalar and pseudoscalar mesons. In particular the ratio of the sigma mass to the pion mass is an interesting measure of the degree of chiral symmetry breaking at different temperatures. We calculate the temperature T* at which M_sigma(T) < 2M_pi(T), above which the sigma partial width into two pions vanishes. We find T*=0.95T_c (where T_c is the critical temperature for the chiral phase transition), within the full effective potential given by the formalism. We find that an expansion a-la Landau of the effective potential around the critical point in the limit of small quark mass provides for a very good determination of T*.

hep-ph↗
arXiv1998

Comparing electroweak data with a decoupling model

Present data, both from direct Higgs search and from analysis of electroweak data, are starting to become rather restrictive on the possible values for the mass of the standard model Higgs. We discuss a new physics scenario based on a model with decoupling (both in a linear and in a non linear version) showing how it allows for an excellent fit to the present values of the $ε$ parameters and how it widens the allowed ranges for the Higgs mass (thought as elementary in the linear version, or as composite in the non linear one).

hep-ph↗
arXiv1998

Algebraic treatment of compactification on noncommutative tori

In this paper we study the compactification conditions of the M theory on D-dimensional noncommutative tori. The main tool used for this analysis is the algebra A(Z^D) of the projective representations of the abelian group Z^D. We exhibit the explicit solutions in the space of the multiplication algebra of A(Z^D), that is the algebra generated by right and left multiplications.

hep-th↗
arXiv1998

Algebras, Derivations and Integrals

In the context of the integration over algebras introduced in a previous paper, we obtain several results for a particular class of associative algebras with identity. The algebras of this class are called self-conjugated, and they include, for instance, the paragrassmann algebras of order $p$, the quaternionic algebra and the toroidal algebras. We study the relation between derivations and integration, proving a generalization of the standard result for the Riemann integral about the translational invariance of the measure and the vanishing of the integral of a total derivative (for convenient boundary conditions). We consider also the possibility, given the integration over an algebra, to define from it the integral over a subalgebra, in a way similar to the usual integration over manifolds. That is projecting out the submanifold in the integration measure. We prove that this is possible for paragrassmann algebras of order $p$, once we consider them as subalgebras of the algebra of the $(p+1)\times(p+1)$ matrices. We find also that the integration over the subalgebra coincides with the integral defined in the direct way. As a by-product we can define the integration over a one-dimensional Grassmann algebra as a trace over $2\times 2$ matrices.

math-ph↗
arXiv1998

Projective Group Algebras

In this paper we apply a recently proposed algebraic theory of integration to projective group algebras. These structures have received some attention in connection with the compactification of the $M$ theory on noncommutative tori. This turns out to be an interesting field of applications, since the space $\hat G$ of the equivalence classes of the vector unitary irreducible representations of the group under examination becomes, in the projective case, a prototype of noncommuting spaces. For vector representations the algebraic integration is equivalent to integrate over $\hat G$. However, its very definition is related only at the structural properties of the group algebra, therefore it is well defined also in the projective case, where the space $\hat G$ has no classical meaning. This allows a generalization of the usual group harmonic analysis. A particular attention is given to abelian groups, which are the relevant ones in the compactification problem, since it is possible, from the previous results, to establish a simple generalization of the ordinary calculus to the associated noncommutative spaces.

math-ph↗