Search results for "massless"
showing 10 items of 191 documents
Building the full Pontecorvo-Maki-Nakagawa-Sakata matrix from six independent Majorana-type phases
2009
In the framework of three light Majorana neutrinos, we show how to reconstruct, through the use of 3 x 3 unitarity, the full PMNS matrix from six independent Majorana-type phases. In particular, we express the strength of Dirac-type CP violation in terms of these Majorana-type phases by writing the area of the unitarity triangles in terms of these phases. We also study how these six Majorana phases appear in CP-odd weak-basis invariants as well as in leptonic asymmetries relevant for flavored leptogenesis.
Double pion photoproduction off nuclei - Are there effects beyond final-state interaction?
2013
Photoproduction of $\pi^{0}\pi^{0}$ and $\pi^{0}\pi^{\pm}$ pairs from nuclei has been measured over a wide mass range ($^2$H, $^{7}$Li, $^{12}$C, $^{40}$Ca, and $^{\rm nat}$Pb) for photon energies from threshold to 600 MeV. The experiments were performed at the MAMI accelerator in Mainz, using the Glasgow photon tagging spectrometer and a 4$\pi$ electromagnetic calorimeter consisting of the Crystal Ball and TAPS detectors. A shift of the pion-pion invariant mass spectra for heavy nuclei to small invariant masses has been observed for $\pi^0$ pairs but also for the mixed-charge pairs. The precise results allow for the first time a model-independent analysis of the influence of pion final-sta…
Photon Scattering with the Lorentz Integral Transform Method
2011
The application of the Lorentz integral transform (LIT) method to photon scattering off nuclei is presented in general. As an example, elastic photon scattering off the deuteron in the unretarded dipole approximation is considered using the LIT method. The inversion of the integral transform is discussed in detail paying particular attention to the high-energy contributions in the resonance term. The obtained E1-polarizabilities are compared to results from the literature. The corresponding theoretical cross section is confronted with experimental results confirming, as already known from previous studies, that the E1-contribution is the most important one at lower energies.
Enhancement of thermal photon production in event-by-event hydrodynamics
2011
Thermal photon emission is widely believed to reflect properties of the earliest, hottest evolution stage of the medium created in ultra-relativistic heavy-ion collisions. Previous computations of photon emission have been carried out using a hydrodynamical medium description with smooth, averaged initial conditions. Recently, more sophisticated hydrodynamical models which calculate observables by averaging over many evolutions with event-by-event fluctuating initial conditions (IC) have been developed. Given their direct connection to the early time dynamics, thermal photon emission appears an ideal observable to probe fluctuations in the medium initial state. In this work, we demonstrate …
Results from the AMANDA telescope
2003
We present results from the AMANDA high energy neutrino telescope located at the South Pole. They include measurements of the atmospheric neutrino flux, search for UHE point sources, and diffuse sources producing electromagnetic/hadronic showers at the detector or close to it.
Two-neutrino double-beta decay of76Ge in an anharmonic vibrator approach
2009
We have calculated the nuclear matrix element of two-neutrino double-beta (2???) decay of 76Ge by using the proton?neutron microscopic anharmonic vibrator approach (pnMAVA). In the pnMAVA the wavefunctions of the intermediate 1+ states in 76As have a one-phonon part containing the proton?neutron QRPA (pnQRPA) phonons and a two-phonon part built by coupling the pnQRPA and charge-conserving QRPA phonons. We compare the measured GT? and GT+ Gamow?Teller strength functions with the measured ones. The two-phonon components of the pnMAVA wavefunctions cause the pnQRPA strength to redistribute over a finite energy range. This has only a small effect on the value 2??? nuclear matrix element. This s…
Massive neutrinos and right-handed weak currents in double beta decay.
1993
The contributions of right-handed weak currents in neutrinoless double beta decay are studied taking explicitly into account the mass corrections to the intermediate neutrino propagator. Due to these corrections the right-handed currents become effective even if all neutrinos are light ([ital m][sub [nu]][gt]10 MeV). Explicit expressions for the neutrino-momentum integrals and the decay half-life are derived. As an example two neutrino-mass scenarios containing the hypothetical 17-keV neutrino are discussed. The experimental half-life of the [sup 76]Ge[r arrow][sup 76]Se decay is used to obtain an upper limit for a new kind of effective right-handed coupling within the two scenarios.
Resonant enhancement of neutrinoless double-electron capture in 152Gd.
2010
In the search for the nuclide with the largest probability for neutrinoless double-electron capture, we have determined the ${Q}_{ϵϵ}$ value between the ground states of $^{152}\mathrm{Gd}$ and $^{152}\mathrm{Sm}$ by Penning-trap mass-ratio measurements. The new ${Q}_{ϵϵ}$ value of 55.70(18) keV results in a half-life of ${10}^{26}\text{ }\text{ }\mathrm{yr}$ for a 1 eV neutrino mass. With this smallest half-life among known $0\ensuremath{\nu}ϵϵ$ transitions, $^{152}\mathrm{Gd}$ is a promising candidate for the search for neutrinoless double-electron capture.
Virtual photons and electrodisintegration of the deuteron
1982
The validity of the virtual photon concept in the analysis of deuteron electrodisintegration for equivalent photon energies up to 300 MeV is investigated. The deuteron and the final state interaction are described by the consistent nonrelativistic calculation of Fabian and Arenhoevel neglecting the effects of meson exchange currents and isobar configurations. We find that in well defined kinematic domains the use of the virtual photon concept is justified in extracting photodisintegration cross sections.
Invisible neutrino decay in precision cosmology
2021
We revisit the topic of invisible neutrino decay in the precision cosmological context, via a first-principles approach to understanding the cosmic microwave background and large-scale structure phenomenology of such a non-standard physics scenario. Assuming an effective Lagrangian in which a heavier standard-model neutrino $\nu_H$ couples to a lighter one $\nu_l$ and a massless scalar particle $\phi$ via a Yukawa interaction, we derive from first principles the complete set of Boltzmann equations, at both the spatially homogeneous and the first-order inhomogeneous levels, for the phase space densities of $\nu_H$, $\nu_l$, and $\phi$ in the presence of the relevant decay and inverse decay p…