arXiv subjects

F. Feruglio

Publications and source records attributed to F. Feruglio.

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↗

arXiv2009

Flavor symmetries, leptogenesis and the absolute neutrino mass scale

We study the interplay between flavor symmetries and leptogenesis in the case when the scale of flavor symmetry breaking is higher than the scale at which lepton number is violated. We show that when the heavy Majorana neutrinos belong to an irreducible representation of the flavor group, all the leptogenesis CP asymmetries vanish in the limit of exact symmetry. In the case of reducible representations we identify a general condition that, if satisfied, guarantees the same result. We then focus on the case of a model in which an $A_4$ flavor symmetry yields a drastic reduction in the number of free parameters, implying that at leading order several quantities are only a function of the lightest neutrino mass $m_l$, which in turn is strongly constrained. For normal ordering (NO) we find m_l\simeq (0.0044 ÷0.0056) eV while for inverted ordering (IO) m_l\gtrsim 0.017 eV. For the 0\nu2βdecay parameter this yields |m_{ee}|\simeq (0.006÷0.007) eV (NO) and |m_{ee}|\gsim 0.017 eV (IO). We show that the leptogenesis CP asymmetries only depend on m_l, on a single non-hierarchical Yukawa coupling y, and on two parameters that quantify the flavor symmetry breaking effects, and we argue that the unflavored regime for leptogenesis is strongly preferred in our model, thus realizing a rather predictive scenario. Performing a calculation of the matter-antimatter asymmetry we find that for NO the observed value is easily reproduced for natural values of the symmetry breaking parameters. For IO successful leptogenesis is possible for a limited choice of the parameters implying rather large reheating temperatures T_reh\gtrsim 5*10^13 GeV.

hep-ph↗

arXiv2009

Revisiting Bimaximal Neutrino Mixing in a Model with S4 Discrete Symmetry

In view of the fact that the data on neutrino mixing are still compatible with a situation where Bimaximal mixing is valid in first approximation and it is then corrected by terms of order of the Cabibbo angle, arising from the diagonalization of the charged lepton masses, we construct a model based on the discrete group S4 where those properties are naturally realized. The model is supersymmetric in 4-dimensions and the complete flavour group is S4 x Z4 x U(1)_FN, which also allows to reproduce the hierarchy of the charged lepton spectrum. The only fine tuning needed in the model is to reproduce the small observed value of r, the ratio between the neutrino mass squared differences. Once the relevant parameters are set to accommodate r then the spectrum of light neutrinos shows a moderate normal hierarchy and is compatible, within large ambiguities, with the constraints from leptogenesis as an explanation of the baryon asymmetry in the Universe.

hep-ph↗

arXiv2000

Report of the Beyond the MSSM Subgroup for the Tevatron Run II SUSY/Higgs Workshop

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal Supersymmetric Standard Model. In other cases, the parameters of the Lagrangian are unusual compared to commonly accepted norms (e.g., Wino LSP, heavy gluino LSP, light gluino, etc.). The phenomenology of supersymmetry varies greatly between the different models. Correspondingly, particular aspects of the detectors assume greater or lesser importance. Detection of supersymmetry and the determination of all parameters may well depend upon having the widest possible view of supersymmetry phenomenology.

hep-ph↗

arXiv1999

Signals of a superlight gravitino at hadron colliders when the other superparticles are heavy

If the gravitino (G) is very light and all the other supersymmetric particles are above threshold, supersymmetry may still be found at colliders, by looking at processes with only gravitinos and ordinary particles in the final state. We compute here the cross-sections for some distinctive signals at hadron colliders: photon plus missing energy, induced by (q antiquark -> G G photon), and jet plus missing energy, induced by (q antiquark -> G G g), (q g -> G G q), and (g g -> G G g). From the present Tevatron data, we estimate the bound m_{3/2} > 2.3 10^-5 eV on the gravitino mass, corresponding to the bound sqrt{F} > 310 GeV on the supersymmetry-breaking scale. We foresee that the upgraded Tevatron and the LHC will be sensitive to values of m_{3/2} up to 4.0 10^-5 eV and 6.2 10^-4 eV, corresponding to sqrt{F} up to 410 GeV and 1.6 TeV, respectively.

hep-ph↗

arXiv1997

Phenomenological aspects of a Fermiophobic SU(2)xSU(2)xU(1) extension of the Standard Model

We consider an extension of the standard electroweak theory with gauge group $SU(2)_L \times SU(2)_R \times U(1)_{\tilde{Y}}$, where the gauge bosons of the extra $SU(2)_R$ factor do not couple to ordinary fermions. We show that precision electroweak data and flavour physics provide quite stringent indirect constraints on its parameter space, but still allow for relatively light non-standard gauge and Higgs bosons. We then consider the model phenomenology at high-energy colliders, and observe that in the gauge boson sector present bounds and possible future signals are dominated by $Z'$ production. In summary, indirect constraints on the charged gauge boson sector are so tight that observable new effects must be connected either with the neutral gauge boson sector or with the extended Higgs sector of the model.

hep-ph↗

arXiv1996

Sum rules for asymptotic form factors in $e^+ e^- -> W^+ W^-$ scattering

At very large energies and in $SU(2)_L\otimes U(1)_Y$ gauge theories, the trilinear gauge boson vertices relevant for $e^+e^- \to W^+W^-$ scattering are related in a simple way to the gauge boson self-energies. We derive these relations, both from the requirement of perturbative unitarity and from the Ward Identities of the theory. Our discussion shows that, in general, it is never possible to neglect vector boson self-energies when computing the form factors which parametrize the $e^+ e^- \to W^+ W^-$ helicity amplitudes. The exclusion of the self-energy contributions would lead to estimates of the effects wrong by orders of magnitudes. We propose a simple way of including the self-energy contributions in an appropriate definition of the form factors.

hep-ph↗

arXiv1996

The fate of the leptophobic Z'

We review the main features of the leptophobic-Z' phenomenology, commenting on the prospects of these models after the recent experimental results on R_c, R_b and after the recent theoretical analyses of jet production at the Tevatron.

hep-ph↗

arXiv1996

Fermion Virtual Effects in $e^+ e^- -> W^+ W^-$ Cross Section

We analyse the contribution of new heavy virtual fermions to the $e^+e^- \rightarrow W^+W^-$ cross section. We find that there exists a relevant interplay between trilinear and bilinear oblique corrections. The result strongly depends on the chiral or vector--like nature of the new fermions. As for the chiral case we consider sequential fermions: one obtains substantial deviation from the Standard model prediction, making the effect possibly detectable at $\sqrt{s}=500$ or $1000$ GeV linear colliders. As an example for the vector--like case we take a SUSY extension with heavy charginos and neutralinos: due to cancellation, the final effect turns out to be negligible.

hep-ph↗

arXiv1996

Phenomenology of Heavy Meson Chiral Lagrangians

The approximate symmetries of Quantum ChromoDynamics in the infinite heavy quark ($Q=c,b$) mass limit ($m_Q \to \infty$) and in the chiral limit for the light quarks ($m_q \to 0,\;q=\,u,\,d,\,s$) can be used together to build up an effective chiral lagrangian for heavy and light mesons describing strong interactions among effective meson fields as well as their couplings to electromagnetic and weak currents, including the relevant symmetry breaking terms. The effective theory includes heavy ($Q \bar q$) mesons of both negative and positive parity, light pseudoscalars, as well as light vector mesons. We summarize the estimates for the parameters entering the effective lagrangian and discuss in particular some phenomenologically important couplings, such as $g_{B^* B π}$. The hyperfine splitting of heavy mesons is discussed in detail. The effective lagrangian allows for the possibility to describe consistently weak couplings of heavy ($B,\, D$) to light ($π,\, ρ, \, K^*,\,$ etc.) mesons. The method has however its own limitations, due to the requirement that the light meson momenta should be small, and we discuss how such limitations can be circumvented through reasonable ansatz on the form factors. Flavour conserving (e. g. $B^* \to B\, γ$) and flavour changing (e. g. $B \to K^* \, γ$) radiative decays provide another field of applications of effective lagrangians; they are discussed together with their phenomenological implications. Finally we analyze effective lagrangians describing heavy charmonium- like ($\bar Q Q$) mesons and their strong and electromagnetic interactions. The role of approximate heavy quark symmetries for this case and the phenomenological tests of these models are also discussed.

hep-ph↗

arXiv1996

Rb, Rc and Jet Distributions at the Tevatron in a Model with an extra vector boson

We show that the reported anomalies in $R_b$ and $R_c$ can be interpreted as the effect of a heavy vector boson \zprime\ universally coupled to $u$- and $d$-type quarks separately and nearly decoupled from leptons. This extra vector boson could then also naturally explain the apparent excess of the jet rate at large transverse momentum observed at CDF.

hep-ph↗

arXiv1996

Searches For New Physics

Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.

hep-ph↗

arXiv1995

Two-loop Corrections for Electroweak Processes

Theoretical uncertainties affecting electroweak observables are reviewed and the relevance of two-loop electroweak radiative corrections for the precision tests of the Standard Model is discussed.

hep-ph↗

arXiv1995

Bounds on Heavy Chiral Fermions

We derive the low-energy electroweak effective lagrangian for the case of additional heavy, unmixed, sequential fermions. Present data still allow for the presence of a new quark and/or lepton doublet with masses greater than $M_Z/2$, provided that these multiplets are sufficiently degenerate. Deviations of the effective lagrangian predictions from a full one-loop computation are sizeable only for fermion masses close to the threshold $M_Z/2$. Some of the constraints on new sequential fermions coming from accelerator results and cosmological considerations are presented. We point out that the new fermions can significantly affect the production and decay rate into $γγ$ of the intermediate Higgs at LHC.

hep-ph↗

arXiv1995

SYMMETRIES FOR VECTOR AND AXIAL-VECTOR MESONS

We discuss the possible symmetries of the effective lagrangian describing interacting pseudoscalar-, vector-, and axial-vector mesons. Specific choices of the parameters give rise to an $[SU(2)\otimes SU(2)]^3$ symmetry. This symmetry can be obtained either {\it á la} Georgi, with all states in the spectrum remaining massless, or in a new realization, implying decoupling of the pseudoscalar bosons from degenerate vector and axial-vector mesons. This second possibility, when minimally coupled with $SU(2)\otimes U(1)$ electroweak gauge vector bosons, seems particularly appealing. All deviations in the low-energy electroweak parameters are strongly suppressed, and the vector and axial-vector states turn out to be quite narrow. A nearby strong electroweak sector would then be conceivable and in principle it could be explored with relatively low energy accelerators.

hep-ph↗

arXiv1994

Two-loop electroweak top corrections: are they under control?

The assumption that two-loop top corrections are well approximated by the $O(G_mu^2 mt^4)$ contribution is investigated. It is shown that in the case of the ratio neutral-to-charged current amplitudes at zero momentum transfer the $O(G_mu^2 mt^2 M_Z^2)$ terms are numerically comparable to the $m_t^4$ contribution for realistic values of the top mass. An estimate of the theoretical error due to unknown two-loop top effect is presented for a few observables of LEP interest.

hep-ph↗

arXiv1994

Heavy Meson Hyperfine Splitting: A Complete $1/m_Q$ Calculation

The hyperfine splittings $Δ_D=(m_{D^*_s}-m_{D_s})-(m_{D^{*+}}-m_{D^+})$ and $Δ_B=(m_{B^*_s}-m_{B_s})-(m_{B^{*0}}-m_{B^0})$ are analyzed in the framework of an effective lagrangian possessing chiral, heavy flavour and spin symmetries, explicitly broken by a complete set of first order terms. Among these terms, those responsible for the difference between the couplings $\gis$ and $\gi$ are evaluated in the QCD sum rules approach. Their contribution to $Δ_D$ and to $Δ_B$ appears to quantitatively balance previously estimated chiral effects nice agreement with the experimental data, solving a suspected puzzle for heavy quark theory.

hep-ph↗

arXiv1994

On the coupling of heavy mesons to pions in QCD

We compute the strong coupling constant $g_{P^* P π}$, with $P$ and $P^*$ respectively pseudoscalar and vector heavy mesons by using the QCD sum rules approach. Our computation is based on the evaluation of the time ordered product of currents between the vacuum and the soft pion state. The so-called parasitic terms are taken into account and give a contribution to the sum rule of the same order of the lowest lying state, while higher dimension non perturbative terms have small numerical effects. The infinite heavy quark mass limit is also examined.

hep-ph↗