Switching the sign of photon induced exchange interactions in semiconductor microcavities with finite quality factors

We investigate coupling of localized spins in a semiconductor quantum dot embedded in a microcavity with a finite quality factor. The lowest cavity mode and the quantum dot exciton are coupled forming a polariton, whereas excitons interact with localized spins via exchange. The finite quality of the cavity Q is incorporated in the model Hamiltonian by adding an imaginary part to the photon frequency. The Hamiltonian, which treats photons, spins and excitons quantum mechanically, is solved exactly. Results for a single polariton clearly demonstrate the existence of a resonance, sharper as the temperature decreases, that shows up as an abrupt change between ferromagnetic and antiferromagnetic indirect anisotropic exchange interaction between localized spins. The origin of this spin-switching finite-quality-factor effect is discussed in detail remarking on its dependence on model parameters, i.e., light-matter coupling, exchange interaction between impurities, detuning and quality factor. For parameters corresponding to the case of a (Cd,Mn)Te quantum dot, the resonance shows up for Q around 70 and detuning around 10 meV. In addition, we show that, for such a quantum dot, and the best cavities actually available (quality factors better than 200) the exchange interaction is scarcely affected.Comment: 7 figures, submitted to PR

Neutrino and antineutrino cross sections in 12^{12}C

We extend the formalism of weak interaction processes, obtaining new expressions for the transition rates, which greatly facilitate numerical calculations, both for neutrino-nucleus reactions and muon capture. We have done a thorough study of exclusive (ground state) properties of $^{12}$B and $^{12}$N within the projected quasiparticle random phase approximation (PQRPA). Good agreement with experimental data is achieved in this way. The inclusive neutrino/antineutrino ($\nu/\tilde{\nu}$) reactions $^{12}$C($\nu,e^-)^{12}$N and $^{12}$C($\tilde{\nu},e^+)^{12}$B are calculated within both the PQRPA, and the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting cross-sections: i) are close to the sum-rule limit at low energy, but significantly smaller than this limit at high energies both for $\nu$ and $\tilde{\nu}$, ii) they steadily increase when the size of the configuration space is augmented, and particulary for $\nu/\tilde{\nu}$ energies $> 200$ MeV, and iii) converge for sufficiently large configuration space and final state spin.Comment: Proceedings of the International Nuclear Physics Conference 2010, Vancouver, BC - Canada 4-9 Jul 201

Superscaling in electroweak excitation of nuclei

Superscaling properties of 12C, 16O and 40Ca nuclear responses, induced by electron and neutrino scattering, are studied for momentum transfer values between 300 and 700 MeV/c. We have defined two indexes to have quantitative estimates of the scaling quality. We have analyzed experimental responses to get the empirical values of the two indexes. We have then investigated the effects of finite dimensions, collective excitations, meson exchange currents, short-range correlations and final state interactions. These effects strongly modify the relativistic Fermi gas scaling functions, but they conserve the scaling properties. We used the scaling functions to predict electron and neutrino cross sections and we tested their validity by comparing them with the cross sections obtained with a full calculation. For electron scattering we also made a comparison with data. We have calculated the total charge-exchange neutrino cross sections for neutrino energies up to 300 MeV.Comment: 19 pages, 12 figures, 1 table; to be published in Physical Review

Many-Body Theory of the Electroweak Nuclear Response

After a brief review of the theoretical description of nuclei based on nonrelativistic many-body theory and realistic hamiltonians, these lectures focus on its application to the analysis of the electroweak response. Special emphasis is given to electron-nucleus scattering, whose experimental study has provided a wealth of information on nuclear structure and dynamics, exposing the limitations of the shell model. The extension of the formalism to the case of neutrino-nucleus interactions, whose quantitative understanding is required to reduce the systematic uncertainty of neutrino oscillation experiments, is also discussed.Comment: Lectures delivered at the DAE-BRNS Workshop on Hadron Physics. Aligarh Muslim University, Aligarh (India), February 18-23, 200

Muon capture on deuteron and 3He

The muon capture reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are studied with conventional or chiral realistic potentials and consistent weak currents. The initial and final A=2 and 3 nuclear wave functions are obtained from the Argonne v18 or chiral N3LO two-nucleon potential, in combination with, respectively, the Urbana IX or chiral N2LO three-nucleon potential in the case of A=3. The weak current consists of polar- and axial-vector components. The former are related to the isovector piece of the electromagnetic current via the conserved-vector-current hypothesis. These and the axial currents are derived either in a meson-exchange or in a chiral effective field theory (chiEFT) framework. There is one parameter (either the N-to-\Delta axial coupling constant in the meson-exchange model, or the strength of a contact term in the chiEFT model) which is fixed by reproducing the Gamow-Teller matrix element in tritium beta-decay. The model dependence relative to the adopted interactions and currents (and cutoff sensitivity in the chiEFT currents) is weak, resulting in total rates of 392.0 +/- 2.3 Hz for A=2, and 1484 +/- 13 Hz for A=3, where the spread accounts for this model dependence.Comment: 15 pages, 1 figure, submitted to Phys. Rev.

Nucleon QCD sum rules in nuclear matter including four-quark condensates

We calculate the nucleon parameters in nuclear matter using the QCD sum rules approach in Fermi gas approximation. Terms up to 1/q^2 in the operator product expansion (OPE) are taken into account. The higher moments of the nucleon structure functions are included. The complete set of the nucleon expectation values of the four-quark operators is employed. Earlier the lack of information on these values has been the main obstacle for the further development of the approach. We show that the four-quark condensates provide the corrections of the order 20% to the results obtained in the leading orders of the OPE. This is consistent with the assumption about the convergence of the OPE. The nucleon vector self-energy \Sigma_v and the nucleon effective mass m^* are expressed in terms of the in-medium values of QCD condensates. The numerical results for these parameters at the saturation value of the density agree with those obtained by the methods of nuclear physics.Comment: 38 pages, 5 figure

Vector meson radiation in relativistic heavy-ion collisions

The sigma-omega model in mean-field approximation where the meson fields are treated classically, describes much of observed nuclear structure and has been employed to describe the nuclear equation of state up to the quark-gluon phase transition. The acceleration of the meson sources, for example, in relativistic heavy-ion collisions, should result in bremsstrahlung-like radiation of the meson fields. The many mesons emitted serve to justify the use of classical meson fields. The slowing of the nuclei during the collision is modeled here as a smooth transition from initial to final velocity. Under ultra-relativistic conditions, vector radiation dominates. The angular distribution of energy flux shows a characteristic shape. It appears that if the vector meson field couples to the conserved baryon current, independent of the baryonic degrees of freedom, this mechanism will contribute to the radiation seen in relativistic heavy-ion collisions. The possible influence of the quark-gluon plasma is also considered.Comment: 17 pages, 4 postscript figures. Uses elsart.sty and psfig.sty. Improved motivation and typographical corrections. Accepted for publication by Nuclear Physics

Neutrino reactions via neutral and charged current by Quasi-particle Random Phase Approximation(QRPA)

We developed the quasi-particle random phase approximation (QRPA) for the neutrino scattering off even-even nuclei via neutral current (NC) and charged cur- rent (CC). The QRPA has been successfully applied for the \beta and \beta\beta decay of relevant nuclei. To describe neutrino scattering, general multipole transitions by weak interactions with a finite momentum transfer are calculated for NC and CC reaction with detailed formalism. Since we consider neutron-proton (np) pairing as well as neutron-neutron (nn) and proton-proton (pp) pairing correlations, the nn + pp QRPA and np QRPA are combined in a framework, which enables to describe both NC and CC reactions in a consistent way. Numerical results for \nu-^{12}C, -^{56}Fe and -^{56}Ni reactions are shown to comply with other theoretical calculations and reproduce well available experimental data

Finite Nuclei in a Relativistic Mean-Field Model with Derivative Couplings

We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski model and one of its variations (the ZM3 model). We calculate energy levels and ground-state properties in nuclei where the mean-field approach is reliable. The role played by the spin-orbit potential in sorting out mean-field model descriptions is emphasized.Comment: 17 pages, 9 figures, 30 kbytes. Uses EPSF.TEX. To appear in Zeit. f. Phys. A (Hadrons and Nuclei

Final-state interactions and superscaling in the semi-relativistic approach to quasielastic electron and neutrino scattering

The semi-relativistic approach to electron and neutrino quasielastic scattering from nuclei is extended to include final-state interactions. Starting with the usual non-relativistic continuum shell model, the problem is relativized by using the semi-relativistic expansion of the current in powers of the initial nucleon momentum and relativistic kinematics. Two different approaches are considered for the final-state interactions: the Smith-Wambach 2p-2h damping model and the Dirac-equation-based potential extracted from a relativistic mean-field plus the Darwin factor. Using the latter the scaling properties of $(e,e')$ and $(\nu_\mu,\mu^-)$ cross sections for intermediate momentum transfers are investigated.Comment: 36 pages, 17 figure