arXiv subjects

F. Caravaglios

Publications and source records attributed to F. Caravaglios.

14 recordsLinked to original sources

arXiv2003

Phenomenological implication of KamLAND on lepton mass matrices

By using a model independent Monte Carlo approach, we study the possible structure of charged and neutral lepton mass matrices, under the assumption of an U(2) horizontal symmetry (additional to the usual Standard Model ones) involving the light fermion generations. We assume the most general Majorana mass matrix for neutrinos. We update the results of our previous similar study, by inserting in the analysis the recent KamLAND data, that contributed to find a final solution to the Solar neutrino problem. The introduction of the new experimental data reduce the allowed regions in the nine dimensional space parameters, and show that our procedure gives stable solutions.

hep-ph↗

arXiv2002

Neutrino masses and non abelian horizontal symmetries

Recent neutrino experiments have made very significant progresses and our knowledge of neutrino masses and mixing has considerably improved. In a model independent Monte Carlo approach, we have examined a very large class of textures, in the context of non abelian horizontal symmetries; we have found that neutrino data select only those charged lepton matrices with left-right asymmetric texture. The large atmospheric mixing angle needs m_{23} ~= m_{33}. This result,if combined with similar recent findings for the quark sector in the B oscillations, can be interpreted as a hint for SU(5) unification. In the neutrino sector strict neutrino anarchy is disfavored by data, and at least a factor 2 of suppression in the first row and column of the neutrino majorana mass matrix is required.

hep-ph↗

arXiv2002

Precision Test of Quark Mass Textures: A Model Independent Approach

Using a Monte Carlo method, we have directly extracted from the available measurements, the hierarchies among the different elements of the quark mass matrices. To do that, we have first introduced a model independent parameterization for two generic class of models: those based on Abelian symmetries and those inspired by a U(2) horizontal symmetry. So, matrix entries are proportional to some epsilon^t, with epsilon<<1 and the t's are different free exponents that we determine from the data through a statistically well defined procedure. We have found that the experimental data poorly constrain the Abelian scenarios. Instead, in non Abelian scenarios, these t-exponents are strongly constrained by the present data. We have found that contrary to a naive U(2) horizontal symmetry expectation, quark mass matrices turn out to be not symmetric. Two solutions emerge: one with M_{32}^{down}>> M_{23}^{down}} and M_{21}^{up}>> M_{12}^{up}; and a second one with slight asymmetries only in the light quark sector, namely M_{21}^{up} < M_{12}^{up} and M_{21}^{down}>M_{12}^{down}.

hep-ph↗

arXiv2001

Indication for Light Sneutrinos and Gauginos from Precision Electroweak Data

The present Standard Model fit of precision data has a low confidence level, and is characterized by a few inconsistencies. We look for supersymmetric effects that could improve the agreement among the electroweak precision measurements and with the direct lower bound on the Higgs mass. We find that this is the case particularly if the 3.6 sigma discrepancy between sin^2 theta_eff from leptonic and hadronic asymmetries is finally settled more on the side of the leptonic ones. After the inclusion of all experimental constraints, our analysis selects light sneutrinos, with masses in the range 55-80 GeV, and charged sleptons with masses just above their experimental limit, possibly with additional effects from light gauginos. The phenomenological implications of this scenario are discussed.

hep-ph↗

arXiv2000

Determination of the CKM unitarity triangle parameters by end 1999

Within the Standard Model, a review of the current determination of the CKM unitarity triangle parameters is presented, using experimental constraints from the measurements of |epsilon_K|, V_ub/V_cb, Delta m_d and from the limit on Delta m_s, available by end 1999.

hep-ph↗

arXiv1998

A new approach to multi-jet calculations in hadron collisions

We present an algorithm to evaluate the exact, tree-level matrix elements for multi-parton processes in QCD. We tested this technique, based on the recursive evaluation of the S-matrix, on processes such as gg -> n gluons and q qbar -> n gluons, with n up to 9. The summation over colour configurations is designed to allow the construction of parton-level event generators suitable to interfacing with a parton-shower evolution including the effects of colour-coherence. This leads to a fully exclusive, hadron-level description of multi-jet final states, accurately incorporating the dynamics of large jet-jet separation angles. Explicit results for the total rates and differential distributions of processes with 8 final-state partons are given.

hep-ph↗

arXiv1997

Electroweak Precision Tests: A Concise Review

1. Introduction 2. Status of the Data 3. Precision Electroweak Data and the Standard Model 4. A More General Analysis of Electroweak Data 4.1 Basic Definitions and Results 4.2 Experimental Determination of the Epsilon Variables 4.3 Comparing the Data with the Minimal Supersymmetric Standard Model 5. Theoretical Limits on the Higgs Mass 6. Conclusion

hep-ph↗

arXiv1997

Event Generators for WW Physics

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.

hep-ph↗

arXiv1997

A Scenario for Contact Interactions at HERA

The four fermion contact interactions, required to explain the anomalous HERA result, could come from the exchange of new heavy (probably composite) resonances. Depending on their charges and quantum numbers, one gets different scenarios and finds that many of these configurations are unsuitable. For example, new neutral resonances seems to be disfavored by the data coming from the TEVATRON, LEP 2 and atomic parity violation. These experiments allow only few helicity combinations that cannot arise from neutral currents in a natural way. On the contrary, a global large symmetry SU(8) * SU(8) (which is contained in SU(16)) embeds some lepto-quarks of spin 1 that could give suitable four fermion interactions (compatible with all other experiments) if these resonances are the lightest new (probably composite) states with a mass comparable to the scale of the contact interactions.

hep-ph↗

arXiv1996

The tau forward-backward Asymmetry within Grand Unified Theories

We will study some possible non universal corrections that could affect single measurements of the Weinberg angle sin^2(theta) (leaving the full average essentially unchanged). We will concentrate on the class of the models that introduces a new light gauge boson and an extended Higgs sector, but we restrict the Higgs charges choice in order to automatically achieve zero mixing at the tree level between the Z_0 and the Z'. This will more naturally keep small the universal effects with a relatively light Z', but it will imply only vector-like coupling between this boson and the standard fermions. A SO(10) gauge boson which distinguishes between families can have such properties and could explain a deviation in the tau forward-backward asymmetry without affecting the tau polarization measurements at LEP.

hep-ph↗

arXiv1996

$e^+ \ e^-$ into 4 fermions + $γ$ with ALPHA

We apply the iterative numerical algorithm ALPHA, which automatically generates the N-point Green functions (as recently suggested \cite{alpha}) to the computation of the production rate of four fermions and four fermions plus photon in electron-positron annihilation. The discussion of the physical results is preceded by an introduction on the algorithm.

hep-ph↗

arXiv1995

An Algorithm to Compute Born Scattering Amplitudes without Feynman Graphs

In this paper we suggest an {\it iterative} algorithm to compute automatically the scattering matrix elements of any given effective lagrangian, $Γ$. By exploiting the relation between $Γ$ and the connected Green function generator, $Z$, we provide a formula which does not require the use of the Feynman graphs and it is suitable to implement a numerical routine. By means of this algorithm we have built a relatively simple and fast fortran code which we have used to calculate, at the tree level, the rate of four fermion production at LEP I\negthinspace{I} (finding a very good agreement with previous calculation) with and without the emission of one observable photon.

hep-ph↗

arXiv1994

Reconciling the LEP and Slac Measurements of Sin^2(Θ_W)

We consider whether a discrepancy between the SLAC and LEP measurements of $\Sw$ can be explained by new physics. We find that only the contribution of a new neutral gauge boson, $Z^\prime$, nearly degenerate with the Z can affect the SLAC measurement while leaving the LEP observables almost unaffected. We briefly discuss possible signals for this new gauge boson, including changes in the $Z$ lineshape when measured with polarised electrons, small changes in $R_b$, $A^e_{FB}$, and larger changes in two jet and $t\bar{t}$ production at hadron colliders.

hep-ph↗

arXiv1994

The Top Mass Upper Bound and Electroweak Radiative Corrections

We investigated the possibility of introducing sizeable negative corrections to the $\varepsilon_{N1}$ ($δρ$) parameter without affecting $\varepsilon_{N3}$. We have found that a proper vector-like family of fermions can imply such corrections. Differently from supersymmetry \cite{bcf}, this can be realized without introducing light particles easily observable at LEP II. Our example can be of particular interest if no new particle is found at LEP II and the $\varepsilon_{N1}$ value is found to be small compared to the one expected in the case of a large top mass.

hep-ph↗