CP and T violation in neutrino oscillations

The conditions to induce appreciable CP-and T-odd effects in neutrino oscillations are discussed. The propagation in matter leads to fake CP-and CPT-odd asymmetries, besides a Bohm-Aharonov type modification of the interference pattern. We study the separation of fake and genuine CP violation by means of energy and distance dependence.

Constraints from lepton universality at the z-peak on unified theories

We suggest the use of a universality-breaking observable based on lepton asymmetries as derived from the left-right asymmetry and the $\tau$ polarization at the $Z$ peak, which can efficiently constrain the parameter space of unified theories. The new observable is complementary to the leptonic partial width differences and it depends critically on the chirality of a possible non-universal $Z$-boson coupling to like-flavour leptons. The LEP/SLC potential of probing universality violation is discussed in representative low-energy extensions of the Standard Model (SM) that could be derived by supersymmetric grand unified theories, such as the SM with left-handed and/or right-handed neutral is…

$\eta -\eta^\prime$ Photoproduction and the Axial Isoscalar Neutral Current Coupling

We show that coherent $\eta$ and $\etap$ photoproduction by means of the Primakoff Effect on the proton depends on the strange component of the neutral axial current coupling. We construct polarization asymmetries that are sensitive to this coupling through the $\gamma - Z$ interference. The $\eta^\prime$ is not a Goldstone boson of a spontaneously broken chiral symmetry, but a phenomenological analysis of the $\eta$ and $\eta^\prime$ production through chiral perturbation theory allows to calculate the observables of interest. The polarized proton or polarized photon asymmetries are predicted to be close to $10^{-4}$ for $-q^2 \sim 0.1-0.5\;\mbox{\rm GeV}^2$.

Neutrino Magnetic Moment and the Process $\nu e \rightarrow \nu e \gamma$

The contribution of a neutrino magnetic moment $\mu_{\nu}$ to the cross section of the process $\nu e^{-}\rightarrow \nu e^{-} \gamma $ has been calculated and compared with the Standard Electroweak one. The radiative process allows to reach low enough values of $Q^2$ without the need to operate at very small energies of recoil electrons. Regions in the phase space which are more favourable to set bounds on $\mu_{\nu}$ are suggested.

Universality-Breaking Effects in Leptonic Z Decays

We analyze the possibility of universality violation in diagonal leptonic decays of the $Z$ boson, in the context of interfamily "see-saw" models. In a minimal extension of the Standard Model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the running $LEP$ experiments.

Weak Interactions at Low Energy

In this series of lectures, I would like to discuss the basic aspects of the standard electroweak theory, as well as some alternatives. The phenomenology associated with charged and neutral currents weak interaction will show the success of the standard theory in giving a quantitative account of the existing data. The framework of most of our considerations will be that of an effective theory at low momentum transfer, low with respect to the masses of the intermediate vector bosons, 80–90 GeV. As an extension of the standard theory for the leptonic sector, I will contemplate the possibility of massive neutrinos being described by Majorana fields, leading to exotic phenomena induced by lepto…

NEUTRINO OSCILLATION AND STELLAR COLLAPSE.

Colloquium: Time-reversal violation with quantum-entangled B mesons

Symmetry transformations have been proven a bedrock tool for understanding the nature of particle interactions, formulating and testing fundamental theories. Based on the up to now unbroken CPT symmetry, the violation of the CP symmetry between matter and antimatter by weak interactions, discovered in the decay of kaons in 1964 and observed more recently in 2001 in B mesons, strongly suggests that the behavior of these particles under weak interactions must also be asymmetric under time reversal T. However, until the recent years there has not been a direct detection of the expected time-reversal violation in the time evolution of any system. This Colloquium examines the field of time-rever…

Dynamical zero in ν¯e–e− scattering and the neutrino magnetic moment

AbstractThe Standard Model differential cross section for ν¯e–e− elastic scattering vanishes exactly, at lowest order, for forward electrons and incident ν¯e energy close to the rest energy of the electron. This dynamical zero is not induced by a fundamental symmetry of the Lagrangian but by a destructive interference between the left- and right-handed chiral couplings of the electron in the charged and neutral current amplitudes. We show that lowest-order analyses based on this favorable kinematic configuration are only mildly affected by the inclusion of the O(α) radiative corrections in the ν¯e–e− differential cross section, thus providing an excellent opportunity for the search of “new …

The tau weak-magnetic dipole moment

We calculate the prediction for the anomalous weak-magnetic form factor of the tau lepton at $q^2=M_Z^2$ within the Standard Model. With all particles on-shell, this is a electroweak gauge invariant quantity. Its value is $a_\tau^w (M_Z^2)= - \;(2.10 + 0.61\, i) \times 10^{-6}$. We show that the transverse and normal components of the single-tau polarization of tau pairs produced at $e^+e^-$ unpolarized collisions are sensitive to the real and absorptive parts of the anomalous weak-magnetic dipole moment of the tau. The sensitivity one can achieve at LEP in the measurement of this dipole moment is discussed.

Tau spin correlations and the anomalous magnetic moment

We show that the precise determination of the Tau magnetic properties is possible in the next generation accelerators, specially at B/Flavour factories. We define spin correlation observables suitable to extract the real part of the magnetic form factor that, for the first time, will allow to test the standard model-QED predictions. In particular, the predicted QED-dependence with both the momentum transfer and the lepton mass can be precisely measured. Until now, the most stringent bounds on the $\tau$ magnetic moment $a_\tau$ come from LEP data with strong assumptions on the physics involved on the observed process. In this paper, we find three different combinations of spin correlations …

New approach for numerical solution of configuration-space Faddeev equations

A new computational scheme for solving the bound state configuration-space Faddeev equations is applied. The scheme is based on the spline-approximation and the adiabatic limit of Faddeev equations. An ordering of variables being in agreement with the limit was chosen. As a result the matrix of the eigenvalue problem has a sparse block structure. Calculations of the bound states of µpp, µdd, µtt mesic molecules and ¯pdd, ¯ptt antiprotonic ones, were performed. To check the method, calculations of the binding energies for such systems as the positronium ion Ps−,3H and3He were carried out. The results are compared with the best results of other authors.

Search for magnetic monopoles with the MoEDAL prototype trapping detector in 8 TeV proton-proton collisions at the LHC

The MoEDAL experiment is designed to search for magnetic monopoles and other highly-ionising particles produced in high-energy collisions at the LHC. The largely passive MoEDAL detector, deployed at Interaction Point 8 on the LHC ring, relies on two dedicated direct detection techniques. The first technique is based on stacks of nuclear-track detectors with surface area $\sim$18 m$^2$, sensitive to particle ionisation exceeding a high threshold. These detectors are analysed offline by optical scanning microscopes. The second technique is based on the trapping of charged particles in an array of roughly 800 kg of aluminium samples. These samples are monitored offline for the presence of trap…

CPT violation in entangled B0–B¯0 states and the demise of flavour tagging

AbstractWe discuss the demise of flavour tagging due to the loss of the particle–antiparticle identity of neutral B-mesons in the Einstein–Podolsky–Rosen correlated states. Such a situation occurs in cases where the CPT operator is ill-defined, as happens, for example, in quantum gravity models with induced decoherence in the matter sector. The time evolution of the perturbed B0–B¯0 initial state, as produced in B-factories, is sufficient to generate new two-body states. For flavour specific decays at equal times, we discuss two definite tests of the two body entanglement: (i) search for the would-be forbidden B0B0 and B¯0B¯0 states; (ii) deviations from the indistinguishable probability be…