arXiv subjects

G. Barenboim

Publications and source records attributed to G. Barenboim.

At least 91 records · Page 5Linked to original sources

arXiv2001

Medium effects for terrestrial and atmospheric neutrino oscillations

Matter effects in neutrino propagation translate into effective parameters for the oscillation and fake CP- and CPT-odd quantities, even in a scenario, such as $Δ_{12}=0$, where no genuine CP violation is present. This fact seems to impose severe restrictions on the determination of intrinsic parameters of the system from long-baseline experiments. We show, however, that the resonance in the effective mixing $\tildeθ_{13}$ can be observed for a certain range of baselines. This provides a way to measure the vacuum mixing angle $θ_{13}$ and the sign of $Δm_{23}^2$ from atmospheric neutrinos, using a detector with energy resolution and charge discrimination.

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arXiv2000

Testing LSND at long-baseline neutrino experiments

Recently it was suggested that two very different mass-squared differences play a role in atmospheric neutrino oscillations. The larger of these also accounts for the LSND result and the smaller of these also drives the solar neutrino oscillations. We consider the predictions of this scheme for long-baseline experiments. We find that high statistics experiments, such as MINOS, can observe a clean signal for this scheme, which is clearly distinguishable from the usual scheme of atmospheric neutrino oscillations driven by a single mass-squared difference.

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arXiv2000

Flavour Violation in SUSY SU(5) GUT at Large tan beta

We study flavour violation in the minimal SUSY SU(5) GUT assuming all the third generation Yukawa couplings to be due to the renormalizable physics above GUT scale. At large $\tanβ,$ as suggested by Yukawa unification in SU(5), sizable flavour violation in the left (right) slepton (down squark) sector is induced due to renormalization effects of down type Yukawa couplings between GUT and Planck scales in addition to the flavour violation in the right slepton sector. The new flavour physics contribution to $K-\bar K,$ $B-\bar B$ mixing is small but might be of phenomenological interest in the case of $b\to sγ.$ The sign of the latter contribution is the same as the sign of the dominant chargino contribution, thus making the constraints on SUSY scale coming from $b\to sγ$ somewhat more restrictive. The most important feature of the considered scenario is the large rate of lepton flavour violation. Given the present experimental constraints, the $μ\to eγ$ and $μ-e$ conversion branching ratios are above the sensitivity of the planned experiments unless the SUSY scale is pushed above one TeV.

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arXiv2000

Tau neutrinos from muon storage rings

Charged tau leptons emerging in a long baseline experiment with a muon storage ring and a far-away detector will positively establish neutrino oscillations. We study the conversion of $ν_μ$ ($\barν_μ$) and of $\barν_e$ ($ν_e$) to $ν_τ$ or $\barν_τ$ for neutrinos from a 20 GeV muon storage ring, within the strong mixing scheme and on the basis of the squared mass differences which are compatible with all reported neutrino anomalies, including the LSND data. In contrast to other solutions which ignore the Los Alamos anomaly, we find charged tau production rates which should be measurable in a realistic set up. As a consequence, determining the complete mass spectrum of neutrinos as well as all three mixing angles seems within reach. Matter effects are discussed thoroughly but are found to be small in this situation.

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arXiv2000

CP Violation with Three Oscillating Neutrino Flavours

We explore the prospects of observing leptonic CP violation in a neutrino factory in the context of a scenario with three strongly oscillating neutrinos able to account for the solar, the atmospheric and the LSND results. We address also the problems related with the fake asymmetries induced by the experimental device and by the presence of matter.

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arXiv1999

CP Asymmetries in B_s Decays and Spontaneous CP violation

We study possible effects of new physics in CP asymmetries in two-body $B_s$ decays in left-right models with spontaneous CP violation. Considering the contributions of new CP phases to the $B_s$ mixing as well as to the penguin dominated decay amplitudes we show that, with the present constraints, large deviations from the standard model predictions in CP asymmetries are allowed in both cases. Detection of the new physics can be done by measuring non-zero asymmetries which are predicted to vanish in the standard model or by comparing two measurements which are predicted to be equal in the standard model. In particular, we show that the measurement of the CKM angle $γ$ in electroweak penguin dominated processes $B_s^0\toρ^0η^{(')}, ρ^0ϕ$ can largely be affected by the new physics.

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arXiv1999

Supersymmetry and CP Violating Asymmetries in $B_{d,s}$ Decays

We study possible effects of supersymmetry (SUSY) in CP asymmetries in non-leptonic $B_{d,s}$ decays in a variety of SUSY flavour models considered in literature. We use both mass insertion and vertex mixing methods to calculate squark-gluino box diagrams contribution to $B_{d,s} - \bar{B}_{d,s}$ mixings. With the squark mixing parameter $η=0.22$, and with large new CP phases, it turns out that the CP asymmetries to be measured in upcoming B-factories, HERA-B and LHC-B, can be completely dominated by the SUSY contribution in almost every considered model. Discrimination between the different models can be done by comparing experimental results in different decay modes. In some models squark masses up to $\sim 5$ TeV can be probed through these experiments provided the SUSY contribution to $B - \bar{B}$ mixing is at 10% level, $|M^{SUSY}_{12}/M_{12}^{SM}|\sim 0.1.$ This implies that models with heavy squarks have a fair chance to be tested in the future CP experiments before LHC.

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arXiv1999

Oscillations, Neutrino Masses and Scales of New Physics

We show that all the available experimental information involving neutrinos can be accounted for within the framework of already existing models where neutrinos have zero mass at tree level, but obtain a small Dirac mass by radiative corrections.

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arXiv1998

CP asymmetries in B0 decays in the left-right model

We study time dependent CP asymmetries in B^0_{d,s} decays in the left-right model with spontaneous breakdown of CP. Due to the new contributions to B^0-\bar B^0 mixing the CP asymmetries can be substantially modified. Moreover, there can be significant new contributions to the $B$-meson decay amplitudes from the magnetic penguins. Most promising for detection of the new physics in the planned $B$ factories is that the CP asymmetries in the decays B--> J/ψK_S and B--> ϕK_S which are supposed to be equal in the standard model can differ significantly in this class of models independently of the results in the measurements of B--> X_s γ.

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arXiv1997

How sensitive to FCNC can $B^0$ CP asymmetries be?

We show that the study of CP asymmetries in neutral B-meson decays provides a very sensitive probe of flavour-changing neutral currents (FCNC). We introduce two new angles, $α_{SM}$ and $β_{SM}$, whose main feature is that they can be readily obtained from the measurement of the CP asymmetries $a_{J/ψK_s}$, $a_{π^+ π^-}$ and the ratio $R_u \equiv|V_{ud}V_{ub}^*|/|V_{cd}V_{cb}^*|$, providing a quantitative test of the presence of new physics in a model-independent way. Assuming that new physics is due to the presence of an isosinglet down-type quark, we indicate how to reconstruct the unitarity quadrangles and point out that the measurements of the above asymmetries, within the expected experimental errors, may detect FCNC effects, even for values of $|\sum_{i=1}^3 V_{id} V_{ib}^* / (V_{td} V_{tb}^*)| $ at the level of a few times $10^{-2}$.

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arXiv1997

$ΔF = 2$ Effective Lagrangian in theories with vector like fermions

In this work we analyze a new piece present in the $ΔF = 2$ effective Lagrangian in models with extra vector-like quarks. This piece, which was not taken into account previously, is required in order to preserve gauge invariance once the unitarity of the CKM matrix is lost. We illustrate the effects of this new piece in both, CP conserving and CP violating processes.

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arXiv1997

Mass of tau neutrino in SO(10) GUT-s

We investigate the allowed ranges of masses for an unstable tau neutrino in the context of SO(10) GUT-s. In light of the new nucleosynthesis results we obtain that there is a narrow window for m_{ν_τ} where the LEP, neutrino oscillation and nucleosynthesis data are compatible. This window, which depends on the effective number of neutrinos contributing to nucleosynthesis, has important cosmological consequences and will be tested by ongoing neutrino oscillation and LEP II experiments.

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arXiv1997

Spontaneous CP violation and the B system

We investigate effects of spontaneous breakdown of CP in $B^0_{d,s}-\overline{B^0}_{d,s}$ systems in left-right symmetric models. Assuming that the left-right contribution to the $B^0-\overline{B^0}$ matrix element $M_{12}$ can be at most equal to the standard model one we obtain a new lower bound, $M_H\gsim 12$ TeV, on the flavour changing Higgs boson mass. Most importantly, the convention independent parameter $Re(\overlineε_B),$ which measures the amount of $ΔB=2$ CP violation, can be enhanced by a factor of four or more for $B^0_d$ and almost by two orders of magnitude for $B^0_s$ systems when compared with the Standard Model predictions. Therefore, interesting possibilities to observe indirect CP violation in the $B$ system are open in the planned facilities.

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arXiv1996

Constraints on doubly charged Higgs interactions at linear collider

Production of a single doubly charged Higgs boson $Delta^{--}$ in polarized $e^+e^-$ and $e^+γ$ collision modes of the linear collider have been investigated. The mass range of $Delta^{--}$ to be probed extends up to the collision energy. The diagonal lepton number violating Yukawa coupling $h_{ee}$ will be tested at least three orders of magnitude more strictly than in present experiments.

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arXiv1996

Constraints on the Wr mass and CP-violation in left-right models

We update the constraints on the right-handed $W_R$ gauge boson mass, mixing angle $ζ$ with the left-handed $W_L$ gauge boson, and other parameters in general left-right symmetric models with different mechanisms of CP violation. Constraints mostly independent of any assumption on the quark sector are obtained from a re-analysis of muon decay data. Estimates of the left-right hadronic matrix elements in the neutral kaon system and their uncertainties are revised using large $N_c$ and Chiral Perturbation Theory arguments. With explicitly given assumptions on the long-distance $(ΔS=1)^2$ contributions to the $K_L-K_S$ mass difference, lower bounds on $M_{W_R}$ are obtained. With the same assumptions, one also gets strong upper bounds from the CP-violating parameter $ε_K$, for most of the parameter space of left-right models where the right-handed third family does not contribute in CP-violating quantities.

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arXiv1996

Left-handed neutrino disappearance probe of neutrino mass and character

We explore the sensitivity to a non vanishing neutrino mass offered by dynamical observables, i.e., branching ratios and polarizations. The longitudinal polarization in the C.M. frame decreases by a 4% for $D^+ \rightarrow τ^+ ν_τ$ and $m_{ν_τ}=24$ MeV. Taking advantage of the fact that the polarization is a Lorentz variant quantity, we study the polarization effects in a boosted frame. By means of a neutrino beam, produced by a high velocity boosted parent able to flip the neutrino helicity, we find that an enhanced left-handed neutrino deficit, induced by a Wigner rotation, appears.

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arXiv1996

Non-decoupling and lepton number violation in left-right models

We argue that large non-decoupling effects of heavy neutrinos can appear naturally in manifestly left-right symmetric models due to the minimization conditions of the scalar potential and the structure of vev's imposed by phenomenology. We derive constraints on off-diagonal light-heavy and heavy-heavy neutrino mixings from the searches for lepton violating decays $μ\rightarrow eγ,$ $μ\rightarrow e e^-e^+$ and $μ-e$ conversion in nuclei. The most stringent limits come from the latter process because its amplitude shows a quadratic non-decoupling dependence on the heavy neutrino mass. Due to the suppression of right-handed currents by large $W_R$ mass the present experiments are not sensitive to the intergenerational mixings between heavy neutrinos if $M_{W_R}>200$ TeV.

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arXiv1996

Spontaneous CP violation in the left-right model and the kaon system

A left-right model with spontaneous $CP$ breakdown, consistent with the particle physics phenomenology, is presented. Constraints on free parameters of the model: mass of the new right handed gauge boson $M_2$ and ratio $r$ of the two vacuum expectation values of the bidoublet, are found from the measurement of $ε$ in the kaon system. For most of the parameter space, $M_2$ is restricted to be below 10 TeV. Higher masses can be achieved only by fine tuning of Kobayashi-Maskawa matrix elements, quark masses, $r$ and the phase $α$ which is the unique source of $CP$-violation in the model. Large number of combinations of signs of quark masses, which are observables of the model, are found to be not allowed since they contradict with data. The range of $ε'/ε$ the model predicts is around $10^{-4}$ in magnitude.

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