arXiv subjects

A. Donini

Publications and source records attributed to A. Donini.

At least 127 records · Page 7Linked to original sources

arXiv2001

Physical Reach of a Neutrino Factory in the 2+2 and 3+1 Four-Family Scenario

We compare the physical reach of a Neutrino Factory in the 2+2 and 3+1 four-family models, with similar results in the two schemes; in both cases huge CP-violating effects can be observed with a near detector in the $ν_μ\to ν_τ$ channel. We also study the capability of long baseline experiments (optimized for the study of the three-family mixing parameter space) in distinguishing a three (active) neutrino model from a four-family scenario.

hep-ph↗

arXiv2001

The 2+2 and 3+1 Four-Family Neutrino Mixing at the Neutrino Factory

We upgrade the study of the physical reach of a Neutrino Factory in the Four Family Neutrino Mixing scenario taking into account the latest LSND results that points out how the 3+1 scheme cannot be completely ruled out within the present experimental data (although the 2+2 scheme is still the preferred choice when four neutrinos are considered). A detailed comparison of the physical reach of the $ν$-factory in the two schemes is given, with similar results for the sensitivity to the mixing angles. Huge CP-violating effects can be observed in both schemes with a near, O(10) Km, detector of O(10) Kton size in the $ν_μ\to ν_τ$ channel. A smaller detector of 1 Kton size can still observe very large effects in this channel.

hep-ph↗

arXiv2001

Four Neutrino Mass Spectra at the Neutrino Factory

We study the physical reach of a Neutrino Factory in the 2+2 and 3+1 Four Neutrino mixing scenarios, with similar results for the sensitivity to the mixing angles. Huge CP-violating effects can be observed in both schemes with a near, O(10) Km, detector of O(10) Kton size in the $ν_μ\to ν_τ$ channel. A smaller detector of 1 Kton size can still observe very large effects in this channel.

hep-ph↗

arXiv2000

CP-violation in 3- and 4-family at the Neutrino Factory

The leptonic CP-violating phase $δ$ can be measured with a Neutrino Factory with $2 \times 10^{20} $ useful muons per year, if the solar neutrino problem is solved by the LMA-MSW solution, with $Δm_{12}^2 \ge 2 \times 10^{-5}$ eV$^2$ (in this analysis a 40 kT magnetized iron detector is considered, taking into account its efficiencies and backgrounds). If LSND is confirmed, CP-violating phenomena in four-family scenarios can be most easily addressed with a small 1 kT detector at $L = \cal O$(10) km (no detailed analysis of the detector efficiencies and backgrounds has been performed in this case).

hep-ph↗

arXiv2000

Golden measurements at a neutrino factory

The precision and discovery potential of a neutrino factory based on muon storage rings is studied. For three-family neutrino oscillations, we analyse how to measure or severely constraint the angle $θ_{13}$, CP violation, MSW effects and the sign of the atmospheric mass difference $Δm^2_{23}$. We present a simple analytical formula for the oscillation probabilities in matter, with all neutrino mass differences non-vanishing, which clarifies the subtleties involved in disentangling the unknown parameters. The appearance of ``wrong-sign muons'' at three reference baselines is considered: 732 km, 3500 km, and 7332 km. We exploit the dependence of the signal on the neutrino energy, and include as well realistic background estimations and detection efficiencies. The optimal baseline turns out to be ${\cal O}(3000$ km). Analyses combining the information from different baselines are also presented.

hep-ph↗

arXiv2000

Update on four-family neutrino oscillations at Neutrino Factory

The prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino, motivated by the $ν_μ\raw ν_e$ LSND signal. Sensitivity to the MNS mixing matrix angles at $O (10^{-3})$ is achieved with a 1 T detector at $\sim 1$ km from the source, whereas leptonic CP-violation can be measured through tau detection with a 1 kT detector at $\sim 100$ km.

hep-ph↗

arXiv2000

Summary of Golden Measurements at a $ν$-Factory

The precision and discovery potential of a neutrino factory based on muon storage rings is summarized. For three-family neutrino oscillations, we analyze how to measure or severely constraint the angle $θ_{13}$, CP violation, MSW effects and the sign of the atmospheric mass difference $Δm^2_{23}$. The appearance of ``wrong-sign muons'' at three reference baselines is considered: 732 km, 3500 km and 7332 km. We exploit the dependence of the signal on the neutrino energy, and include as well realistic background estimations and detection efficiencies. The optimal baseline turns out to be $O$(3000 km).

hep-ph↗

arXiv2000

Delta M_K and epsilon_K in SUSY at the Next-to-Leading order

We perform a Next-to-Leading order analysis of Delta S=2 processes beyond the Standard Model. Combining the recently computed NLO anomalous dimensions and the B parameters of the most general Delta S=2 effective Hamiltonian, we give an analytic formula for Delta M_K and epsilon_K in terms of the Wilson coefficients at the high energy scale. This expression can be used for any extension of the Standard Model with new heavy particles. Using this result, we consider gluino-mediated contributions to Delta S=2 transitions in general SUSY models and provide an improved analysis of the constraints on off-diagonal mass terms between the first two generations of down-type squarks. Finally, we improve the constraints on R-violating couplings from Delta M_K and epsilon_K.

hep-ph↗

arXiv2000

Four species neutrino oscillations at $ν$-Factory: sensitivity and CP-violation

The prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino. We consider the $ν_μ\raw ν_e$ LSND signal. Its associated large mass difference leads to observable neutrino oscillations at short ($\sim 1$ km) baseline experiments. Sensitivities to the leptonic angles down to $10^{-3}$ can be easily achieved with a 1 Ton detector. Longer baseline experiments ($\sim 100$ km) with a 1 Kton detector can provide very clean tests of CP-violation especially through tau lepton detection.

hep-ph↗

arXiv2000

Fat Brane Phenomena

Gravitons could permeate extra space dimensions inaccessible to all other particles, which would be confined to ``branes''. We point out that these branes could be ``fat'' and have a non-vanishing width in the dimensions reserved for gravitons. In this case the other particles, confined within a finite width, should have ``branon'' excitations. Chiral fermions behave differently from bosons under dimensional reduction, and they may --or may not-- be more localized than bosons. All these possibilities are in principle testable and distinguishable, they could yield spectacular signatures at colliders, such as the production of the first branon excitation of $γ$'s or $Z$'s, decaying into their ground state plus a quasi-continuum of graviton recurrences. We explore these ideas in the realm of a future lepton collider and we individuate a {\it dimensiometer}: an observable that would cleanly diagnose the number of large ``extra'' dimensions.

hep-ph↗

arXiv1999

Renormalization Group Invariant Matrix Elements of DS = 2 and DI = 3/2 Four-Fermion Operators without Quark Masses

We introduce a new parameterization of four-fermion operator matrix elements which does not involve quark masses and thus allows a reduction of systematic uncertainties. In order to simplify the matching between lattice and continuum renormalization schemes, we express our results in terms of renormalization group invariant B-parameters which are renormalization-scheme and scale independent. As an application of our proposal, matrix elements of DI=3/2 and SUSY DS =2 operators have been computed. The calculations have been performed using the tree-level improved Clover lattice action at two different values of the strong coupling constant (beta=6/g^2=6.0 and 6.2), in the quenched approximation. Renormalization constants and mixing coefficients of lattice operators have been obtained non-perturbatively. Using lowest order ChiPT, we also obtain ^{NDR}_{I=2} = (0.11\pm 0.02) GeV^4 and ^{NDR}_{I=2} = (0.51\pm 0.05) GeV^4 at mu=2 GeV.

hep-lat↗

arXiv1999

Matrix Elements without Quark Masses on the Lattice

We introduce a new parameterization of four-fermion matrix elements which does not involve quark masses and thus allows a reduction of systematic uncertainties in physical amplitudes. As a result the apparent quadratic dependence of e'/e on m_s is removed. To simplify the matching between lattice and continuum renormalization schemes, we express our results in terms of Renormalization Group Invariant B-parameters which are renormalization-scheme and scale independent. As an application of our proposal, matrix elements of DeltaI=3/2 and SUSY DeltaF=2 ($F=S,C,B$) four-fermion operators have been computed.

hep-lat↗

arXiv1999

Neutrino mixing and CP-violation

The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.

hep-ph↗

arXiv1999

Winding Modes and Large Extra Dimensions

We review briefly the main features of the Large Extra Dimensions scenario in the framework of weakly coupled Type I string theory. Kaluza-Klein (KK) excitations of the graviton are expected, whereas no KK modes for the gauge bosons arise if the gauge group is tied to a D3-brane. In this scenario, typical signatures such as direct production of KK modes of the graviton at high-energy colliders could test the size of the compactified dimensions. We point out that contrary to what considered in the literature on the subject, in the general case of anisotropic compactification Winding Modes of the Standard Model gauge bosons could also be directly observable, thus further constraining the model.

hep-ph↗

arXiv1999

B-parameters for DeltaS = 2 Supersymmetric Operators

We present a calculation of the matrix elements of the most general set of DeltaS=2 dimension-six four-fermion operators. The values of the matrix elements are given in terms of the corresponding B-parameters. Our results can be used in many phenomenological applications, since the operators considered here give important contributions to K^0--K^0bar mixing in several extensions of the Standard Model (supersymmetry, left-right symmetric models, multi-Higgs models etc.). The determination of the matrix elements improves the accuracy of the phenomenological analyses intended to put bounds on basic parameters of the different models, as for example the pattern of the sfermion mass matrices. The calculation has been performed on the lattice, using the tree-level improved Clover action at two different values of the strong coupling constant (beta=6/g_0^2(a)=6.0 and 6.2, corresponding to a^-1= 2.1 and 2.7 GeV respectively), in the quenched approximation. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively.

hep-lat↗

arXiv1999

Anisotropic Type I String Compactification, Winding Modes and Large Extra Dimensions

We discuss the structure of general Anisotropic Compactification in Type I D=4, N=1 string theory. It is emphasized that, in this context, a possible interpretation of M_{Planck} as ``dual'' to (at least) one of the Kaluza-Klein or Windings Modes could provide interesting interpretations of the ``physical scales'' and the GUT coupling. Some of the scenarios presented here are strictly connected with the phenomenological proposal of TeV-scale gravity (i.e. millimiter compactification). We show that in this scenario new and probably dominant effects should arise from the presence of ``low-energy'' Winding Modes of usual SM particles. Stringent bounds on the Planck mass in 4+n dimensions are derived from the existing experimental limits on massive replicas of SM gauge bosons. Non-observation of Winding Modes at the planned accelerators could provide stronger bounds on the 4+n dimensional Planck mass than those from graviton emission into the bulk. Some comments on other possible phenomenological interesting scenarios are addressed.

hep-ph↗

arXiv1999

Non-Perturbative Renormalization of Lattice Four-Fermion Operators without Power Subtractions

A general non-perturbative analysis of the renormalization properties of $ΔI=3/2$ four-fermion operators in the framework of lattice regularization with Wilson fermions is presented. We discuss the non-perturbative determination of the operator renormalization constants in the lattice Regularization Independent (RI or MOM) scheme. We also discuss the determination of the finite lattice subtraction coefficients from Ward Identities. We prove that, at large external virtualities, the determination of the lattice mixing coefficients, obtained using the RI renormalization scheme, is equivalent to that based on Ward Identities, in the continuum and chiral limits. As a feasibility study of our method, we compute the mixing matrix at several renormalization scales, for three values of the lattice coupling $β$, using the Wilson and tree-level improved SW-Clover actions.

hep-lat↗

arXiv1998

Quenched Supersymmetry

We study the effects of quenching in Super-Yang-Mills theory. While supersymmetry is broken, the lagrangian acquires a new flavour U(1 | 1) symmetry. The anomaly structure thus differs from the unquenched case. We derive the corresponding low-energy effective lagrangian. As a consequence, we predict the mass splitting expected in numerical simulations for particles belonging to the lowest-lying supermultiplet. An estimate of the systematic error due to quenching follows.

hep-th↗