119284838
Physical range of majorana neutrino mixing parameters
If neutrinos are Majorana fermions, the lepton mixing parameter space consists of six mixing parameters: three mixing angles and three CP-odd phases. A related issue concerns the physical range of the mixing parameters. What values should these take so that all physically distinguishable mixing scenarios are realized? We present a detailed discussion of the lepton mixing parameter space in the case of two and three active neutrinos and in the case of three active and N sterile neutrinos. We emphasize that this question, which has been a source of confusion even among neutrino physicists, is connected to an unambiguous definition of the neutrino mass eigenstates. We find that all Majorana phases can always be constrained to lie between 0 and {pi}, and that all mixing angles can be chosen positive and at most less than or equal to {pi}/2 provided the Dirac phases are allowed to vary between -{pi} and {pi}. We illustrate our results with several examples. Finally, we point out that, in the case of new flavor-changing neutrino interactions, the lepton mixing parameter space may need to be enlarged. We properly qualify this statement, and offer concrete examples.
121227319
What is the Energy Scale of the Physics Responsible for Neutrino Masses
The observed tiny but non-zero neutrino masses are often interpreted as evidence for new physics at energy scales above 1010 TeV. This statement is based on several assumptions, including (a) neutrinos are Ma-jorana fermions, (b) the physics responsible for neutrino masses is not very weakly coupled, and (c) the new physics sector – responsible for lepton number breaking – couples to the Standard Model in a 'simple' way. We point out that the issue of the energy scale associated to neutrino masses is far from a resolved and that we should turn to data in order to elucidate it. In particular, if one opts out of (c), the new physics responsible for neutrino masses could be associated to energy scales anywhere between 0.1 and 1012 TeV, even if one assumes that the new physics couplings to the standard model are order one. We study the neutrino phenomenology of all possible effective operators that break lepton number by two units and use those as estimates of the effect of 'all' models of high energy lepton-number breaking. We then estimate the effects of these different types of new physics on other lepton-number violating observables, including neutrinoless double-beta decay, collider signatures, and rare meson decays.
119115901
Pseudo-Dirac Neutrinos in the New Standard Model
The addition of gauge-singlet fermions to the standard model Lagrangian renders the neutrinos massive and allows one to explain all that is experimentally known about neutrino masses and lepton mixing by varying the values of the Majorana mass parameters M for the gauge singlets and the neutrino Yukawa couplings {lambda}. Here we explore the region of parameter space where M values are much smaller than the neutrino Dirac masses {lambda}v. In this region, neutrinos are pseudo-Dirac fermions. We find that current solar data constrain M values to be less than at least 10{sup -9} eV, and discuss the sensitivity of future experiments to tiny gauge-singlet fermion masses. We also discuss a useful basis for analyzing pseudo-Dirac neutrino mixing effects. In particular, we identify a simple relationship between elements of M and the induced enlarged mixing matrix and new mass-squared differences. These allow one to directly relate bounds on the new mass-squared differences to bounds on the singlet fermion Majorana masses.
118402093
Minimally Allowed beta beta 0 nu Rates From Approximate Flavor Symmetries
Neutrinoless double beta decay ({beta}{beta}0{nu}) is the only realistic probe of Majorana neutrinos. In the standard scenario, dominated by light neutrino exchange, the process amplitude is proportional to m{sub ee} , the e - e element of the Majorana mass matrix. This is expected to hold true for small {beta}{beta}{nu} rates ({Gamma}{sub {beta}{beta}0{nu}}), even in the presence of new physics. Naively, current data allows for vanishing m{sub ee} , but this should be protected by an appropriate flavor symmetry. All such symmetries lead to mass matrices inconsistent with oscillation phenomenology. Hence, Majorana neutrinos imply nonzero {Gamma}{sub {beta}{beta}0{nu}}. I perform a spurion analysis to break all possible abelian symmetries that guarantee {Gamma}{sub {beta}{beta}0{nu}} = 0 and search for minimally allowed m{sub ee} values. Specifically, I survey 259 broken structures to yield m{sub ee} values and current phenomenological constraints under a variety of scenarios. This analysis also extracts predictions for both neutrino oscillation parameters and kinematic quantities. Assuming reasonable tuning levels, I find that m{sub ee} > 4 x 10{sup -6} eV at 99% confidence. Bounds below this value would indicate the Dirac neutrino nature or the existence of new light (eV-MeV scale) degrees of freedom that can potentially be probed elsewhere.more » This limit can be raised by improvements in neutrino parameter measurements, particularly of the reactor mixing angle, depending on the best fit parameter values. Such improvements will also significantly constrain the available model space and aid in future constructions.« less
15898659
Semileptonic decays of light quarks beyond the Standard Model
We thank the Institute for Nuclear Theory at the University of Washington and the 
Aspen Center for Physics for their hospitality during the completion of this work. We thank 
Antonio Pich and Jorge Portoles for useful comments. M.G.-A. thanks A. Filipuzzi for useful 
comments and discussions and the LANL T-2 Group for its hospitality and partial support. 
This work has been supported in part by the EU RTN network FLAVIAnet [Contract No. 
MRTN-CT-2006-035482], by MICINN, Spain [Grants FPU No. AP20050910, FPA2007- 
60323 and Consolider-Ingenio 2010 Programme CSD2007-00042 -CPAN-] (M. G.-A.). This 
work was performed under the auspices of the National Nuclear Security Administration 
of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. 
DE-AC52-06NA25396, and was supported in part by the LANL LDRD program.
1539910
A phenomenological study of photon production in low energy neutrino nucleon scattering
Low energy photon production is an important background to many current and future precision neutrino experiments. We present a phenomenological study of t-channel radiative corrections to neutral current neutrino nucleus scattering. After introducing the relevant processes and phenomenological coupling constants, we will explore the derived energy and angular distributions as well as total cross-section predictions along their estimated uncertainties. This is supplemented throughout with comments on possible experimental signatures and implications. We conclude with a general discussion of the analysis in the context of complimentary methodologies.
122775679
An equivalence theorem for a massive spin one particle interacting with Dirac particles in quantum field theory
The (1,0)(+)(0,1) massive spin one field phi mu nu (x) is quantized following the method of Takahashi and Umezawa (1953). The interaction Hamiltonian in the interaction picture is then calculated for such a field interacting in a simple way with Dirac fields. In contrast with a remark of Kyriakopoulos (1969) the generalized Matthews' theorem is found to apply to the calculation of S matrix elements. The analogous theory in terms of the Proca field is given in outline, and the two theories are found to be inequivalent. A discussion of how the inequivalence arises is given; then it is demonstrated how equivalent theories may be constructed, and the equivalence is proved.
122863150
Comments on the paper «Equivalence theorems for massive spin-one particles»
119812514
Causality, Lorentz invariance and i) the electromagnetic interaction of a massive spin-one vector field with arbitrary magnetic-dipole moment, ii) the massive Yang-Mills field
In recent years, following the methods first used by VwLo and ZWANZmER (1), several authors have studied the causal na ture of the propagat ion of higher-spin classical fields in external potentials (3). By a consideration of several examples involving a massive spin-one vector field, the author has lent force to the conjecture that , for a field in an external potential , the classical theory is causal (in the sense of VELo and ZWA~ZlGER) if and only if the corresponding quantum theory is Lorentz invar iant (in the sense tha t there exists an operator ordering in terms of which the per turba t ion expansion for the S-operator is normal-independent) (3). I t is of interest to see if the results of ref. (3) can be extended to include interactions between classical fields, and the corresponding fully quantized theories. As a first step in this direction, two theories, whose Lorentz invariance propert ies at the fully quantized level are well known, are here considered at the classical level. The first theory to be discussed is the electromagnetic interact ion of a massive spinone vector field with a rb i t ra ry magnetic-dipole moment. This theory was found b y L ~ and YA~G to be noncovariant a t the fully quantized level (4). Later , NAKAI~UEA (6) and Tzou (e) demonstra ted that , by the inclusion of an appropria te fourth-degree selfinteract ion of the vector field into the Lee-Yang theory, a Lorentzinvar iant theory results. Since i t is the magnetic-dipole interaction, and not the minimal electromagnetic interaction, which gives rise to the covariance difficulties, the la t te r will, for caleulat ional and notat ional simplicity, be omit ted from the following discussion. Thus the
123580085
The relationship between causality, in a classical relativistic field theory, and Lorentz invariance in the corresponding quantum theory, for a massive spin-one field in external potentials
A massive spin-one field, interacting with external potentials, is described in terms of the Stuckelberg formalism (1938). Some points, concerning necessary and sufficient conditions for the classical theory to be causal, in the sense of Velo and Zwanziger (1969 and 1971) are clarified. It is then shown that with a simple restriction on the type of interaction considered, the classical theory is causal, in the above sense, if and only if the corresponding quantum theory is Lorentz invariant, in that the S operator in the interaction picture is normal independent. Incidental in this demonstration is the result that the characteristic and Lee-Yang determinants share the same form. It is indicated how this result generalized to interactions between Stuckelberg, Klein-Gordon and electromagnetic fields and the validity of the result, in the more usual vector formalism is established.
119352130
Chandra multi-wavelength plane (ChaMPlane) survey: design and initial results
The Chandra Multiwavength Plane (ChaMPlane) Survey of the galactic plane incorporates serendipitous sources from selected Chandra pointings in or near the galactic plane (b 10-100), neutron stars and black holes (quiescent low mass X-ray binaries) to constrain their space densities and thus origin and evolution. Secondary objectives are to identify Be stars in high mass X-ray binaries and constrain their space densities, and to survey the H-R diagram for stellar coronal sources. A parallel optical imaging under the NOAO Long Term Survey program provides deep optical images using the Mosaic imager on the CTIO and KPNO 4-m telescopes. The 36′ × 36′ optical images (Hα, R, V and I) cover ∼ 5× the area of each enclosed Chandra ACIS FOV, providing an extended survey of emission line objects for comparison with Chandra. Spectroscopic followup of optical counterparts is then conducted, thus far with WIYN and Magellan. The X-ray preliminary results from both the Chandra and optical surveys will be presented, including logN-logS vs. galactic position (l,b) and optical identifications.