arXiv subjects

S. Rigolin

Publications and source records attributed to S. Rigolin.

At least 37 records · Page 2Linked to original sources

arXiv2007

Neutrino hierarchy from CP-blind observables with high density magnetized detectors

High density magnetized detectors are well suited to exploit the outstanding purity and intensities of novel neutrino sources like Neutrino Factories and Beta Beams. They can also provide independent measurements of leptonic mixing parameters through the observation of atmospheric muon-neutrinos. In this paper, we discuss the combination of these observables from a multi-kton iron detector and a high energy Beta Beam; in particular, we demonstrate that even with moderate detector granularities the neutrino mass hierarchy can be determined for $θ_{13}$ values greater than 4$^\circ$.

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arXiv2007

Phenomenology of symmetry breaking from extra dimensions

Motivated by the electroweak hierarchy problem, we consider theories with two extra dimensions in which the four-dimensional scalar fields are components of gauge boson in full space. We explore the Nielsen-Olesen instability for SU(N) on a torus, in the presence of a magnetic background. A field theory approach is developed, computing explicitly the minimum of the complete effective potential, including tri-linear and quartic couplings and determining the symmetries of the stable vacua. We also develop appropriate gauge-fixing terms when both Kaluza-Klein and Landau levels are present and interacting, discussing the interplay between the possible six and four dimensional choices. The equivalence between coordinate dependent and constant Scherk-Schwarz boundary conditions -associated to either continuous or discrete Wilson lines- is analyzed.

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arXiv2006

A Beta Beam complex based on the machine upgrades for the LHC

The Beta Beam CERN design is based on the present LHC injection complex and its physics reach is mainly limited by the maximum rigidity of the SPS. In fact, some of the scenarios for the machine upgrades of the LHC, particularly the construction of a fast cycling 1 TeV injector (``Super-SPS''), are very synergic with the construction of a higher $γ$ Beta Beam. At the energies that can be reached by this machine, we demonstrate that dense calorimeters can already be used for the detection of $ν$ at the far location. Even at moderate masses (40 kton) as the ones imposed by the use of existing underground halls at Gran Sasso, the CP reach is very large for any value of $θ_{13}$ that would provide evidence of $ν_e$ appearance at T2K or NO$ν$A ($θ_{13}\geq 3^\circ$). Exploitation of matter effects at the CERN to Gran Sasso distance provides sensitivity to the neutrino mass hierarchy in significant areas of the $θ_{13}-δ$ plane.

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arXiv2006

$ν_μ$ disappearance at the SPL, T2K-I, NO$ν$A and the Neutrino Factory

We study the measurement of the atmospheric neutrino oscillation parameters, $θ_{23}$ and $Δm^2_{23}$, at the $ν_μ$ disappearance channel at three conventional beam facilities, the SPL, T2K-phase I and NO$ν$A. These two parameters have been shown to be of crucial importance in the measurement of two of the unknowns of the PMNS mixing matrix, $θ_{13}$ and the leptonic CP-violating phase $δ$. In our analyis, the effect of the two discrete ambiguities, ${\rm sign}(Δm^2_{23})$ and ${\rm sign}(\tan 2 θ_{23})$, is explicitly taken into account. We analyse also the $ν_μ$ disappearance channel at the Neutrino Factory, and combine it with the ``golden'' $ν_e \to ν_μ$ and ``silver'' $ν_e \to ν_τ$ appearance channels to study its impact on the measurement of $θ_{13}$ and $δ$. Eventually, we present the sensitivity of the four facilities to different observables: $θ_{13}$, $δ$, maximal $θ_{23}$, the sign of the atmospheric mass difference, $s_{atm}$, and the $θ_{23}$-octant, $s_{oct}$.

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arXiv2005

Perspectives for a neutrino program based on the upgrades of the CERN accelerator complex

In this paper, we discuss the possibilities offered to neutrino physics by the upgrades of the CERN accelerator complex. Emphasis is on the physics reach of a medium $γ$ (350-580) $β$-beam that fully exploits the improvements in the CERN accelerator complex for the luminosity/energy upgrade of the LHC. We show that, this design not only profits of the ongoing efforts for the upgrades of the LHC, but also leverage out the existing infrastructures of the LNGS underground laboratory. Furthermore, given the involved high neutrino energies, above 1 GeV, a non-magnetized iron detector could efficiently exploit the neutrino beam. We show that the performance of this complex for what concerns the discovery of the CP violation in the leptonic sector, in case $θ_{13}$ is discovered by Phase I experiments, is comparable with the current baseline design based on a gigantic water Cherenkov at Frejus. Furthermore, this complex has also some sensitivity to the neutrino mass hierarchy.

hep-ph↗

arXiv2005

The impact of solar and atmospheric parameter uncertainties on the measurement of $θ_{13}$ and $δ$

We present in this paper the analysis of the measurement of the unknown PMNS parameters $θ_{13}$ and $δ$ at future LBL facilities performing complete three parameters fits, each time fully including in the fit one of the atmospheric and solar oscillation parameters within its present (future) error. We show that, due to the presence of degeneracies, present uncertainties on $θ_{23}$ and $Δm^2_{23}$ worsen significantly the precision on ($θ_{13}$,$δ$) at future LBL experiments. Only if a precision on the atmospheric parameters at least similar to what expected at T2K-I is reached, then the sensitivities to $θ_{13}$ and $δ$ that have been presented in the literature for many facilities (where $θ_{23}$ and $Δm^2_{23}$ are generally considered as fixed external inputs) can indeed be almost recovered.On the other hand, the impact on this measurement of the uncertainties on the solar parameters, $θ_{12}$ and $Δm^2_{12}$ is already negligible. Our analysis has been performed using three reference setups: the SPL Super-Beam and the standard low-$γ$ $β$-Beam, both aiming toward a Mton Water Čerenkov detector located at L=130 km; the 50 GeV Neutrino Factory with a 40 kton Magnetized Iron Detector to look for the ``golden channel'' $ν_e \to ν_μ$ with baseline L=3000 km and a 4 kton Emulsion Cloud Chamber to look for the ``silver channel'' $ν_e \to ν_τ$ with baseline L=732 km.

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arXiv2005

Physics reach of $β$-beams and $ν$-factories: the problem of degeneracies

We discuss the physics reach of $β$-Beams and $ν$-Factories from a theoretical perspective, having as a guideline the problem of degeneracies. The presence of degenerate solutions in the measure of the neutrino oscillation parameters $θ_{13}$ and $δ$ is, in fact, the main problem that have to be addressed in planning future neutrino oscillation experiments. If degeneracies are not (at least partially) solved, it will be almost impossible to perform, at any future facility, precise measurements of $θ_{13}$ and/or $δ$. After a pedagogical introduction on why degenerate solutions arise and how we can get rid of them, we analyze the physics reach of current $β$-beam and $ν$-factory configurations. The physics reach of the "standard" \BB is severely affected by degeneracies while a better result can be obtained by higher-$γ$ setups. At the \NF the combination of Golden and Silver channels can solve the eightfold degeneracy down to $\sin^2θ_{13} \le 10^{-3}$

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arXiv2005

$ν_μ$ disappearance at the SPL, T2K-I and the Neutrino Factory

We study the $ν_μ$ disappearance channel at T2K-phase I and the SPL and analyse the achievable reduction of present uncertainties in $θ_{23}$ and $Δm^2_{23}$. We analyse the impact of discrete ambiguities in sign($Δm^2{23}$) and sign($2 \tan θ_{23}$). We show how the disappearance channel at the Neutrino Factory is complementary to the ``golden'' and ``silver'' appearance channels and can be used to reduce the eightfold-ambiguity problem in ($θ_{13}-δ$).

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arXiv2005

Appearance and disappearance signals at a beta-Beam and a Super-Beam facility

In this letter we present the study of the eightfold degeneracy in the $(θ_{13},δ)$ measurement including both appearance and disappearance channels. We analyse, for definiteness, the case of a standard low-$γ$ $β$-Beam and a 4 MWatt SPL Super-Beam facility, both aiming at a UNO-like Mton water Cerenkov detector located at the Frejus laboratory, $L = 130$ km. In the $β$-Beam case, the \nue disappearance channel does not improve the $(θ_{13},δ)$ measurement when a realistic (i.e. $\ge$ 2%) systematic error is included. In the Super-Beam case, the \numu disappearance channel could, instead, be quite useful in reducing the impact of the eightfold degeneracy in the $(θ_{13},δ)$ measurement, especially once the error on the atmospheric mass difference is fully taken into account in the fit.

hep-ph↗

arXiv2004

Degeneracies at a beta-Beam and a Super-Beam Facility

The presence of degeneracies can considerably worsen the measure of the neutrino oscillation parameters $θ_{13}$ and $δ$. We study the physics reach of a specific ``CERN'' setup, using a standard $β$-Beam and Super-Beam facility. These facilities have a similar sensitivity in both parameters. Their combination does not provide any dramatic improvement as expected due to their almost identical L/E ratio. We analyse if adding the correspondent disappearance channels can help in reducing the effect of degeneracies in the $(θ_{13},δ)$ measure.

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arXiv2004

Why care about $(θ_{13},δ)$ degeneracy at future neutrino experiments

The presence of several clone solutions in the simultaneous measurement of ($θ_{13},δ$) has been widely discussed in literature. Here, after a pedagogical introduction on why these clones arise, we discuss how the clones location in the ($θ_{13},δ$) plane change as a function of the physical input pair ($\barθ_{13},\barδ$). We compare the clone flow of a set of possible future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory proposals. We show that the combination of these specific BetaBeam and SuperBeam could not help in solving the degeneracies. The combination of one of them with the Neutrino Factory Golden and Silver channel can, instead, be used to solve completely the eightfold degeneracy.

hep-ph↗

arXiv2004

Study of the eightfold degeneracy with a standard $β$-Beam and a Super-Beam facility

The study of the eightfold degeneracy at a neutrino complex that includes a standard $β$-Beam and a Super-Beam facility is presented for the first time in this paper. The scenario where the neutrinos are sent toward a Megaton water Cerenkov detector located at the Fréjus laboratory (baseline 130 Km) is exploited. The performance in terms of sensitivity for measuring the continuous ($θ_{13}$ and $δ$) and discrete (${sign} [ Δm^2_{23} ]$ and ${sign} [\tan (2θ_{23}) ]$) oscillation parameters for the $β$-Beam and Super-Beam alone, and for their combination has been studied. A brief review of the present uncertainties on the neutrino and antineutrino cross-sections is also reported and their impact on the discovery potential discussed.

hep-ph↗

arXiv2003

Clone flow analysis for a theory inspired Neutrino Experiment planning

The presence of several clone solutions in the simultaneous measurement of ($θ_{13},δ$) has been widely discussed in literature. In this letter we write the analytical formulae of the clones location in the ($θ_{13},δ$) plane as a function of the physical input pair ($\barθ_{13},\barδ$). We show how the clones move with changing $\barθ_{13}$. The "clone flow" can be significantly different if computed (naively) from the oscillation probabilities or (exactly) from the probabilities integrated over the neutrino flux and cross-section. Using our complete computation we compare the clone flow of a set of possible future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory proposals. We show that the combination of these specific BetaBeam and SuperBeam does not help in solving the degeneracies. On the contrary, the combination of one of them with the Neutrino Factory Golden and Silver channel can be used, from a theoretical point of view, to solve completely the eightfold degeneracy.

hep-ph↗

arXiv2002

Supersymmetric Pati-Salam Models from Intersecting D-Branes

We explore supersymmetric Type I string-motivated three-family scenarios in which the Standard Model is embedded within two sets of intersecting D branes with U(1)-extended Pati-Salam gauge groups. We study a model inspired by the Shiu-Tye Type IIB orientifold, in which a three-family scenario is obtained by assuming that the gauge symmetry breaking takes place in two stages; the Pati-Salam group arises from diagonal breaking of the U(N) gauge groups, which is then broken to the SM gauge group. We investigate the diagonal breaking scenario in detail and find that generically there are difficulties involved in decoupling the exotic Higgs remnants. On the phenomenological side, proper low energy gauge coupling predictions effectively lead to a ``single brane'' scenario for M_string of order 10^16 GeV. The soft parameters in this limit are constrained by a well-known sum rule, leading to a distinctive phenomenological pattern for the low energy mass spectrum.

hep-ph↗

arXiv2001

Alternative approach to $b->s γ$ in the uMSSM

The gluino contributions to the $C'_{7,8}$ Wilson coefficients for $b->s γ$ are calculated within the unconstrained MSSM. New stringent bounds on the $δ^{RL}_{23}$ and $δ^{RR}_{23}$ mass insertion parameters are obtained in the limit in which the SM and SUSY contributions to $C_{7,8}$ approximately cancel. Such a cancellation can plausibly appear within several classes of SUSY breaking models in which the trilinear couplings exhibit a factorized structure proportional to the Yukawa matrices. Assuming this cancellation takes place, we perform an analysis of the $b->s γ$ decay. We show that in a supersymmetric world such an alternative is reasonable and it is possible to saturate the $b->s γ$ branching ratio and produce a CP asymmetry of up to 20%, from only the gluino contribution to $C'_{7,8}$ coefficients. Using photon polarization a LR asymmetry can be defined that in principle allows for the $C_{7,8}$ and $C'_{7,8}$ contributions to the $b->s γ$ decay to be disentangled. In this scenario no constraints on the ``sign of $μ$'' can be derived.

hep-ph↗

arXiv2001

Top Dipole Form Factors and Loop-induced CP-violation in Supersymmetry

The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of the top quark are presented. Far from the Z peak, they are not sufficient to account for all the new physics effects. In the context of the calculation of the process e^+e^- -> t tbar to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.

hep-ph↗

arXiv2001

Dipole Form Factors and Loop-induced CP-violation in Supersymmetry

The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of heavy fermions are reviewed. For the $Z$ boson on shell, the weak-magnetic and weak-electric dipole moments of the $τ$ lepton and the $b$ quark can be defined and directly connected to observables. But far from the $Z$ peak, the weak and electromagnetic dipole form factors are not enough to account for all the new physics effects. In the context of the calculation of the process $e^+e^-\to t\bar{t}$ to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The set of tensor integrals employed, the one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.

hep-ph↗

arXiv2001

Decoupling Properties of MSSM particles in Higgs and Top Decays

We study the supersymmetric (SUSY) QCD radiative corrections, at the one-loop level, to $h^0$, $H^{\pm}$ and t quark decays, in the context of the Minimal Supersymmetric Standard Model (MSSM) and in the decoupling limit. The decoupling behaviour of the various MSSM sectors is analyzed in some special cases, where some or all of the SUSY mass parameters become large as compared to the electroweak scale. We show that in the decoupling limit of both large SUSY mass parameters and large CP-odd Higgs mass, the $Γ(h^0\to b \bar b)$ decay width approaches its Standard Model value at one loop, with the onset of decoupling being delayed for large $\tanβ$ values. However, this decoupling does not occur if just the SUSY mass parameters are taken large. A similar interesting non-decoupling behaviour, also enhanced by $\tanβ$, is found in the SUSY-QCD corrections to the $Γ(H^+\to t \bar b)$ decay width at one loop. In contrast, the SUSY-QCD corrections in the $Γ(t\to W^+ b)$ decay width do decouple and this decoupling is fast.

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