1,001 research outputs found
Vacuum oscillations of quasi degenerate solar neutrinos
The atmospheric neutrino oscillations and the vacuum oscillation solution of
the solar neutrino problem can be consistently described by a doubly or triply
degenerate neutrino spectrum as long as the high level of degeneracy required
is not spoiled by radiative corrections. We show that this is the case for
neutrino mass matrices generated by symmetries. This imposes a strong
constraint on the mixing angles and requires the mixing should be close to
bi-maximal. We briefly discuss the relevance of our results for the
measurability of the neutrino spectrum.Comment: 6 pages. Final version, more clear presentatio
Graviton loops and brane observables
We discuss how to consistently perform effective Lagrangian computations in
quantum gravity with branes in compact extra dimensions. A reparametrization
invariant and infrared finite result is obtained in a non trivial way. It is
crucial to properly account for brane fluctuations and to correctly identify
physical observables. Our results correct some confusing claims in the
literature. We discuss the implications of graviton loops on electroweak
precision observables and on the muon g-2 in models with large extra
dimensions. We model the leading effects, not controlled by effective field
theory, by introducing a hard momentum cut-off.Comment: 9 pages + 4 eps figures, JHEP style latex document. The paper is
composed by a theoretical part, followed (after page 21) by a
phenomenological part. v2: version published in JHEP, few typos corrected.
v3: few additional typos corrected in the Appendi
Epsilon' from supersymmetry with non universal A terms?
In supersymmetric theories with a motivated flavour structure, we investigate
the possibility that an epsilon' parameter as large as the measured value be
generated without conflicting with the bounds from electron and neutron
electric dipoles and mu --> e gamma.Comment: 8 pages. v2: we have cancelled hep-ph/9510303 as a motivation for non
universal A terms, because it is wrong. v3,4: A significant sign error
corrected. Conclusions unchange
Stabilization of the Electroweak Vacuum by a Scalar Threshold Effect
We show how a heavy scalar singlet with a large vacuum expectation value can
evade the potential instability of the Standard Model electroweak vacuum. The
quartic interaction between the heavy scalar singlet and the Higgs doublet
leads to a positive tree-level threshold correction for the Higgs quartic
coupling, which is very effective in stabilizing the potential. We provide
examples, such as the see-saw, invisible axion and unitarized Higgs inflation,
where the proposed mechanism is automatically implemented in well-defined
ranges of Higgs masses.Comment: 18 pages, 5 figure
Oscillations of solar and atmospheric neutrinos
Motivated by recent results from SuperKamiokande, we study both solar and
atmospheric neutrino fluxes in the context of oscillations of the three known
neutrinos. We aim at a global view which identifies the various possibilities,
rather than attempting the most accurate determination of the parameters of
each scenario. For solar neutrinos we emphasise the importance of performing a
general analysis, independent of any particular solar model and we consider the
possibility that any one of the techniques --- chlorine, gallium or water
Cerenkov --- has a large unknown systematic error, so that its results should
be discarded. The atmospheric neutrino anomaly is studied by paying special
attention to the ratios of upward and downward going nu_e and nu_mu fluxes.
Both anomalies can be described in a minimal scheme where the respective
oscillation frequencies are widely separated or in non-minimal schemes with two
comparable oscillation frequencies. We discuss explicit forms of neutrino mass
matrices in which both atmospheric and solar neutrino fluxes are explained. In
the minimal scheme we identify only two `zeroth order' textures that can result
from unbroken symmetries. Finally we discuss experimental strategies for the
determination of the various oscillation parameters.Comment: 20 pages, 7 figures. Final version: one reference added; fit of
atmospheric neutrinos improve
The likelihood for supernova neutrino analyses
We derive the event-by-event likelihood that allows to extract the complete
information contained in the energy, time and direction of supernova neutrinos,
and specify it in the case of SN1987A data. We resolve discrepancies in the
previous literature, numerically relevant already in the concrete case of
SN1987A data.Comment: 7 pages, 2 figures. Accepted for publication in PR
Massive and Massless Neutrinos on Unbalanced Seesaws
The observation of neutrino oscillations requires new physics beyond the
standard model (SM). A SM-like gauge theory with p lepton families can be
extended by introducing q heavy right-handed Majorana neutrinos but preserving
its SU(2)_L x U(1)_Y gauge symmetry. The overall neutrino mass matrix M turns
out to be a symmetric (p+q) x (p+q) matrix. Given p>q, the rank of M is in
general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The
existence of (p-q) massless left-handed Majorana neutrinos is an exact
consequence of the model, independent of the usual approximation made in
deriving the Type-I seesaw relation between the effective p x p light Majorana
neutrino mass matrix M_\nu and the q x q heavy Majorana neutrino mass matrix
M_R. In other words, the numbers of massive left- and right-handed neutrinos
are fairly matched. A good example to illustrate this seesaw fair play rule is
the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits
on the unbalanced seesaw.Comment: RevTex 8 pages, 1 PS figure. Two crucial references adde
Anthropic solution to the magnetic muon anomaly: the charged see-saw
We present models of new physics that can explain the muon g-2 anomaly in
accord with with the assumption that the only scalar existing at the weak scale
is the Higgs, as suggested by anthropic selection. Such models are dubbed
"charged see-saw" because the muon mass term is mediated by heavy leptons. The
electroweak contribution to the g-2 gets modified by order one factors, giving
an anomaly of the same order as the observed hint, which is strongly correlated
with a modification of the Higgs coupling to the muon.Comment: 21 pages, many equations despite the first word in the title. v3:
loop function G_WN corrected, conclusions unchange
Muon and Tau Neutrinos Spectra from Solar Flares
Solar neutrino flares and mixing are considered. Most power-full solar flare
as the ones occurred on 23th February 1956, September 29th 1989, 28th October
and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino
bursts. These flares took place both on front or in the edge and in the hidden
solar disk. The observed and estimated total flare energy should be a source of
a prompt secondary neutrino burst originated, by proton-proton-pion production
on the sun itself; a more delayed and spread neutrino flux signal arise by the
solar charged flare particles reaching the terrestrial atmosphere. Our first
estimates of neutrino signals in largest underground detectors hint for few
events in correlation with, gamma,radio onser. Our approximated spectra for
muons and taus from these rare solar eruption are shown over the most common
background. The muon and tau signature is very peculiar and characteristic over
electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be
detectable above the minimal muon threshold of 113 MeV. The rarest tau
appearence will be possible only for hardest solar neutrino energies above
3.471 GeVComment: 14 pages, 4 figures, Vulcano Conference 200
Fricke and polymer gel 2D dosimetry validation using Monte Carlo simulation
Complexity in modern radiotherapy treatments demands advanced dosimetry systems for quality control. These systems must have several characteristics, such as high spatial resolution, tissue equivalence, three-dimensional resolution, and dose-integrating capabilities. In this scenario, gel dosimetry has proved to be a very promising option for quality assurance. In this study, the feasibility of Fricke and polymer gel dosimeters suitably shaped in form of thin layers and optically analyzed by visible light transmission imaging has been investigated for quality assurance in external radiotherapy. Dosimeter irradiation was carried out with a 6-MV photon beam (CLINAC 600C). The analysis of the irradiated dosimeters was done using two-dimensional optical transmission images. These dosimeters were compared with a treatment plan system using Monte Carlo simulations as a reference by means of a gamma test with parameters of 1 mm and 2%. Results show very good agreement between the different dosimetric systems: in the worst-case scenario, 98% of the analyzed points meet the test quality requirements. Therefore, gel dosimetry may be considered as a potential tool for the validation of other dosimetric systems.Fil: Vedelago, José Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Chacón Obando, D.. Universidad Nacional. Physics Department; Costa Rica. Universidad Nacional de Córdoba; ArgentinaFil: Malano, Francisco Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Conejeros, R.. Servicio de Radioterapia, Icos. Temuco, Chile;Fil: Figueroa, R.. Universidad de la Frontera; ChileFil: Garcia, D.. Servicio de Imagenes por Resonancia Magnética; ChileFil: González, G.. Servicio de Imagenes por Resonancia Magnética; ChileFil: Romero, Marcelo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Santibañez, M.. Servicio de Imagenes por Resonancia Magnética; ChileFil: Strumia, Miriam Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Velásquez, J.. Servicio de Radioterapia; ChileFil: Mattea, Facundo. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Valente, M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad de La Frontera. Departamento de Ciencias Físicas; Chil
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