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.
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.
117798634
Non-oscillation probes of the neutrino mass hierarchy and vanishing |U(e3)|
One of the outstanding issues in neutrino physics is the experimental determination of the neutrino mass hierarchy: Is the order of the neutrino masses ``normal'' - m_1^2<m_2^2<m_3^2 - or is it inverted - m_3^2<m_1^2<m_2^2, with m_2^2-m_1^2 << m_2^2,m_1^2? While this issue can be resolved in next-generation long-baseline nu_{mu} to nu_e neutrino oscillation studies if |U_{e3}|^2 is large enough, a clear strategy on how to resolve it if |U_{e3}|^2 is sufficiently small is still lacking. We study the capability of non-oscillation probes of neutrino masses to determine the neutrino mass ordering. We concentrate on studies of m_{nu_e}, the kinematical neutrino mass to which precise studies of tritium beta-decay are sensitive, m_{ee}, the effective mass to which the rate for neutrinoless double-beta decay is sensitive if the neutrinos are Majorana fermions, and Sigma, the sum of the neutrino masses, to which cosmological probes of the energy budget of the Universe are sensitive. We find that combined measurements of m_{ee}, Sigma, and m_{nu_e} are capable of establishing the neutrino mass hierarchy if these measurements are precise enough and if one ``gets lucky.'' We quantify the previous sentence in detail by performing a numerical analysis of a large number of theoretical data sets, for different measured values of m_{nu_e}, m_{ee}, and Sigma, keeping in mind the ultimate sensitivity that can be reached by next (and next-to-next) generation experiments.
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.
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.
122901453
Some remarks on an equivalence theorem for an interacting massive spin one particle in quantum field theory
The quantization of a massive spin one particle field, satisfying the first order system of equations due to Proca, is summarized. The interaction of such a field with an arbitrary field is then considered. Equivalent theories in terms of vector and antisymmetric second rank tensor spin one fields are then constructed in a simple manner, providing a generalization of an equivalence theorem due to the author. In addition, this approach, involving the use of first order systems of equations, allows a simple extension to the case of equivalence theorems for arbitrary integral spin. The nature of this extension is indicated.
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.
120287965
Some remarks on causality, Lorentz invariance and the generalized Matthews' rule for a massive spin one vector field in an external potential
A massive spin one vector field is quantized in the presence of an external potential, with source linear in the vector field, to provide an illustration of the aspects of a quantum theory in an external potential, which are reflections of the causal nature of the corresponding classical theory. In the examples considered, the S operator of the quantum theory is found to be Lorentz invariant or not, according as the corresponding classical theory is causal or not. The normal dependence of the interaction hamiltonian, and the applicability of the generalized Matthews' rule are also discussed.
118501099
Daughters and Weinberg field theory
SummaryA recurrence relation is obtained for the Feynman amplitude for the scattering of four spinless particles due to the exchange of a particle with spinJ, described by a (J, 0) field of Weinberg. It is shown that lower-spin contributions still occur in the amplitude, even though there are no redundant components in the spinor field.RiassuntoSi ottiene una relazione di ricorrenza per l'ampiezza di Feynmann dello scattering di quattro particelle prive di spin dovuto allo scambio di una particella di spinJ, descritto da un campo (J, 0) di Weinberg. Si dimostra che nell'ampiezza si ha ancora il contributo dello spin minore, anche se nel campo spinoriale non si hanno componenti ridondanti.РезюмеПолучается рекурентное соотношение для фейнмановской амплитуды рассеяния четырех бесспиновых частиц, обусловленное обменом частицы со спиномJ, которая описывается (J, 0) полем Вейнберга. Показывается, что в амплитуде все же имеется вклад от более низкого спина, даже если не существуют ишбыточные компоненты в спинорном поле.
121923701
Constraints, causality and Lorentz invariance
Simple theories of interacting classical relativistic massive spin-1 and spin-3/2 fields are studied. In these examples, it is found that if a theory is acausal in the sense of Velo and Zwanziger, it is also not Lorentz covariant. The breakdown of Lorentz covariance is seen to manifest itself in the constraints, which must be satisfied by the interacting fields, not determining all the dependent fields components simultaneously in all inertial frames of reference. Some remarks on the present state of massive spin-3/2 theories are made.