arXiv subjects

M. Masip

Publications and source records attributed to M. Masip.

At least 37 records · Page 2Linked to original sources

arXiv2009

Atmospheric lepton fluxes at ultrahigh energies

In order to estimate the possibility to observe exotic physics in a neutrino telescope, it is essential to first understand the flux of atmospheric neutrinos, muons and dimuons. We study the production of these leptons by high-energy cosmic rays. We identify three main sources of muons of energy E > 10^6 GeV: the weak decay of charm and bottom mesons and the electromagnetic decay of unflavored mesons. Contrary to the standard assumption, we find that eta mesons, not the prompt decay of charm hadrons, are the dominant source of atmospheric muons at these energies. We show that, as a consequence, the ratio between the neutrino and muon fluxes is significantly reduced. For dimuons, which may be a background for long-lived staus produced near a neutrino telescope, we find that pairs of E ~ 10^7 GeV forming an angle above 10^-6 rad are produced through D (80%) or B (10%) meson decay and through Drell-Yan proceses (10%). The frequency of all these processes has been evaluated using the jet code PYTHIA.

hep-ph↗

arXiv2009

Galactic magnetic fields and the large-scale anisotropy at MILAGRO

The air-shower observatory Milagro has detected a large-scale anisotropy of unknown origin in the flux of TeV cosmic rays. We propose that this anisotropy is caused by galactic magnetic fields, in particular, that it results from the combined effects of the regular and the turbulent (fluctuating) magnetic fields in our vicinity. Instead of a diffusion equation, we integrate Boltzmann's equation to show that the turbulence may define a preferred direction in the cosmic-ray propagation that is orthogonal to the local regular magnetic field. The approximate dipole anisotropy that we obtain explains well Milagro's data.

astro-ph.HE↗

arXiv2009

Heavy neutrino decay at SHALON

The SHALON Cherenkov telescope has recorded over 2x10^6 extensive air showers during the past 17 years. The analysis of the signal at different zenith angles (θ) has included observations from the sub-horizontal direction θ=97^o. This inclination defines an Earth skimming trajectory with 7 km of air and around 1000 km of rock in front of the telescope. During a period of 324 hours of observation, after a cut of shower-like events that may be caused by chaotic sky flashes or reflections on the snow of vertical showers, we have detected 5 air showers of TeV energies. We argue that these events may be caused by the decay of a long-lived penetrating particle entering the atmosphere from the ground and decaying in front of the telescope. We show that this particle can not be a muon or a tau lepton. As a possible explanation, we discuss two scenarios with an unstable neutrino of mass m\approx 0.5 GeV and cτ\approx 30 m. Remarkably, one of these models has been recently proposed to explain an excess of electron-like neutrino events at MiniBooNE.

hep-ph↗

arXiv2007

Exotic physics with ultrahigh energy cosmic rays

Ultrahigh energy cosmic rays provide a unique ground for probing new physics. In this talk we review the possibility of testing TeV gravity in interactions of cosmogenic neutrinos and the potential to discover long-lived exotic particles in nucleon-produced air showers, such as gluinos of split-SUSY models or staus of supersymmetric models with a gravitino LSP.

hep-ph↗

arXiv2007

Little Higgs models with a light T quark

We study Little Higgs models based on a SU(3)_1 x SU(3)_2 global symmetry and with two scales (the two vacuum expectation values f_{1,2}) substantially different. We show that all the extra vector boson fields present in these models may be much heavier than the vectorlike T quark necessary to cancel top-quark quadratic corrections. In this case the models become an extension of the standard model with a light (500 GeV) T quark and a scalar Higgs field with a large singlet component. We obtain that the Yukawa and the gauge couplings of the Higgs are smaller than in the standard model, a fact that reduces significantly the Higgs production rate through glu-glu and WW fusion. The T-quark decay into Higgs boson becomes then a dominant Higgs production channel in hadron colliders.

hep-ph↗

arXiv2007

New physics from ultrahigh energy cosmic rays

Cosmic rays from outer space enter the atmosphere with energies of up to 10^{11} GeV. The initial particle or a secondary hadron inside the shower may then interact with an air nucleon to produce nonstandard particles. In this article we study the production of new physics by high energy cosmic rays, focusing on the long-lived gluino of split-SUSY models and a WIMP working as dark matter. We first deduce the total flux of hadron events at any depth in the atmosphere, showing that secondary hadrons can not be neglected. Then we use these results to find the flux of gluinos and WIMPs that reach the ground after being produced inside air showers. We also evaluate the probability of producing these exotic particles in a single proton shower of ultrahigh energy. Finally we discuss the possible signal in current and projected experiments. While the tiny flux of WIMPs does not seem to have any phenomenological consequences, we show that the gluinos could modify substantially the profile of a small fraction of extensive air showers. In particular, they could produce a distinct signal observable at AUGER in showers of large zenith angle.

hep-ph↗

arXiv2006

Probing TeV gravity at neutrino telescopes

Models with extra dimensions and the fundamental scale at the TeV could imply sign als in large neutrino telescopes due to gravitational scattering of cosmogenic neu trinos in the detection volume. Apart from the production of microscopic black hol es, extensively studied in the literature, we present gravity-mediated interactions at larger distances, that can be calculated in the e ikonal approximation. In these elastic processes the neutrino loses a small fracti on of energy to a hadronic shower and keeps going. The event rate of these events is higher than that of black hole formation and the signal is distinct: no charged leptons and possibly multiple-bang events.

hep-ph↗

arXiv2005

TeV gravity at neutrino telescopes

Cosmogenic neutrinos reach the Earth with energies around 10^9 GeV, and their interactions with matter will be measured in upcoming experiments (Auger, IceCube). Models with extra dimensions and the fundamental scale at the TeV could imply signals in these experiments. In particular, the production of microscopic black holes by cosmogenic neutrinos has been extensively studied in the literature. Here we make a complete analysis of gravity-mediated interactions at larger distances, where they can be calculated in the eikonal approximation. In these processes a neutrino of energy E_νinteracts elastically with a parton inside a nucleon, loses a small fraction y of its energy, and starts a hadronic shower of energy y E_ν<< E_ν. We analyze the ultraviolet dependence and the relevance of graviton emission in these processes, and show that they are negligible. We also study the energy distribution of cosmogenic events in AMANDA and IceCube and the possibility of multiple-bang events. For any neutrino flux, the observation of an enhanced rate of neutral current events above 100 TeV in neutrino telescopes could be explained by TeV-gravity interactions. The values of the fundamental scale of gravity that IceCube could reach are comparable to those to be explored at the LHC.

hep-ph↗

arXiv2005

A Little Higgs model of neutrino masses

Little Higgs models are formulated as effective theories with a cut-off of up to 100 times the electroweak scale. Neutrino masses are then a puzzle, since the usual see-saw mechanism involves a much higher scale that would introduce quadratic corrections to the Higgs mass parameter. We propose a model that can naturally accommodate the observed neutrino masses and mixings in Little Higgs scenarios. Our framework does not involve any large scale or suppressed Yukawa couplings, and it implies the presence of three extra (Dirac) neutrinos at the TeV scale. The masses of the light neutrinos are induced radiatively, they are proportional to small (\approx keV) mass parameters that break lepton number and are suppressed by the Little Higgs cut-off.

hep-ph↗

arXiv2004

Cosmogenic neutrinos and signals of TeV gravity in air showers and neutrino telescopes

The existence of extra dimensions allows the possibility that the fundamental scale of gravity is at the TeV. If that is the case, gravity could dominate the interactions of ultra-high energy cosmic rays. In particular, the production of microscopic black holes by cosmogenic neutrinos has been estimated in a number of papers. We consider here gravity-mediated interactions at larger distances, where they can be calculated in the eikonal approximation. We show that for the expected flux of cosmogenic neutrinos these elastic processes give a stronger signal than black hole production in neutrino telescopes. Taking the bounds on the higher dimensional Planck mass M_D (D=4+n) from current air shower experiments, for n=2 (6) elastic collisions could produce up to 118 (34) events per year at IceCube. On the other hand, the absence of any signal would imply a bound of M_D>~5 TeV.

hep-ph↗

arXiv2004

Mini-review on Lepton Flavor and CP Violation in SUSY

Lepton flavor and CP violation in supersymmetric models are briefly reviewed. After a short motivation and an introduction to the phenomenology, model independent constraints on mass insertions, predictions of SUSY GUT models and rates for several LFV and CPV processes are presented.

hep-ph↗

arXiv2004

Strongest gravitational waves from neutrino oscillations at supernova core bounce

Resonant active-to-active ($ν_a \to ν_a$), as well as active-to-sterile ($ν_a \to ν_s$) neutrino ($ν$) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases antineutrino ($\barν$) mean free paths, and thus its luminosity. Because the oscillation feeds mass-energy into the target $ν$ species, the large mass-squared difference between species ($ν_a \to ν_s$) implies a huge amount of energy to be given off as gravitational waves ($L_{\textrm{GWs}} \sim 10^{49}$ erg s$^{-1}$), due to anisotropic but coherent $ν$ flow over the oscillation length. This asymmetric $ν$-flux is driven by both the spin-magnetic and the {\it universal spin-rotation} coupling. The novel contribution of this paper stems from 1) the new computation of the anisotropy parameter $α\sim 0.1-0.01$, and 2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino $ν_s$ that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et {\it al.} (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from $ν$ difussion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts the more promissing supernova gravitational-wave signal that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.

astro-ph↗

arXiv2003

Neutrino Mixing and Lepton Flavor Violation in SUSY-GUT Models

In supersymmetric (SUSY) models the misalignment between fermion and sfermion families introduces unsuppressed flavor-changing processes. Even if the mass parameters are chosen to give no flavor violation, family dependent radiative corrections make this adjustment not stable. In particular, due to the observed large neutrino mixings and potentially large neutrino Yukawa couplings, sizable lepton flavor violation (LFV) is expected. After introducing the basic concepts, the framework and the main assumptions, we report on a recent study of rare leptonic decays in a class of SUSY-GUT models with three quasi-degenerate neutrinos. We show that LFV effects are likely visible in forthcoming experiments.

hep-ph↗

arXiv2003

Flavour Changing Neutral Currents in Intersecting Brane Models

Intersecting D-brane models provide an attractive explanation of family replication in the context of string theory. We show, however, that the localization of fermion families at different brane intersections in the extra dimensions introduces flavour changing neutral currents mediated by the Kaluza-Klein excitations of the gauge fields. This is a generic feature in these models, and it implies stringent bounds on the mass of the lightest Kaluza-Klein modes (becoming severe when the compactification radii are larger than the string length). We present the full string calculation of four-fermion interactions in models with intersecting D-branes, recovering the field theory result. This reveals other stringy sources of flavour violation, which give bounds that are complementary to the KK bounds (i.e. they become severe when the compactification radii are comparable to the string length). Taken together these bounds imply that the string scale is larger than $M_s\gtrsim 10^2$ TeV, implying that non-supersymmetric cases are phenomenologically disfavoured.

hep-ph↗

arXiv2002

Lepton Flavor Violation in Z and Lepton Decays in Supersymmetric Models

The observation of charged lepton flavor non-conservation would be a clear signature of physics beyond the Standard Model. In particular, supersymmetric (SUSY) models introduce mixings in the sneutrino and the charged slepton sectors which could imply flavor-changing processes at rates accessible to upcoming experiments. In this paper we analyze the possibility to observe Z --> lep_I lep_J in the GigaZ option of TESLA at DESY. We show that although models with SUSY masses above the current limits could predict a branching ratio BR(Z --> mu e) accessible to the experiment, they would imply an unobserved rate of mu --> e gamma and thus are excluded. In models with a small mixing angle between the first and the third (or the second and the third) slepton families GigaZ could observe Z --> tau mu (or Z --> tau e) consistently with present bounds on lep_J --> lep_I gamma. In contrast, if the mixing angles between the three slepton families are large the bounds from mu --> e gamma push these processes below the reach of GigaZ. We show that in this case the masses of the three slepton families must be strongly degenerated (with mass differences of order 10^{-3}). We update the limits on the slepton mass insertions delta_{LL,RR,LR} and discuss the correlation between flavor changing and g_mu-2 in SUSY models.

hep-ph↗

arXiv2002

Cosmic Rays and New Physics at the TeV: the Neutrino-Nucleon Cross Section

Ultrahigh energy neutrinos can be used to explore the physics at the TeV scale. We study the neutrino-nucleon cross section in models with extra dimensions and the fundamental scale at the TeV. In particular, we discuss the production of string resonances and the gravitational interactions (multigraviton exchange and production of microscopic black holes) in these models. We show that the new TeV physics could give observable signals in horizontal air showers and neutrino telescopes.

hep-ph↗

arXiv2001

TeV Strings and the Neutrino-Nucleon Cross Section at Ultra-high Energies

In scenarios with the fundamental unification scale at the TeV one expects string excitations of the standard model fields at accessible energies. We study the neutrino-nucleon cross section in these models. We show that duality of the scattering amplitude forces the existence of a tower of massive leptoquarks that mediate the process in the s-channel. Using the narrow-width approximation we find a sum rule for the production rate of resonances with different spin at each mass level. We show that these contributions can increase substantially the standard model neutrino-nucleon cross section, although seem insufficient in order to explain the cosmic ray events above the GZK cutoff energy.

hep-ph↗

arXiv2000

Ultraviolet dependence of Kaluza-Klein effects on electroweak observables

In extensions of the standard model (SM) with d extra dimensions at the TeV scale the virtual exchange of Kaluza-Klein (KK) excitations of the gauge bosons gives contributions that change the SM relations between electroweak observables. These corrections are finite only for d=1; for d\ge 2 the infinite tower of KK modes gives a divergent contribution that has to be regularized introducing a cutoff (the string scale). However, the ultraviolet dependence of the KK effects is completely different if the running of the couplings with the scale is taken into account. We find that for larger d the number of excitations at each KK level increases, but their larger number is compensated by the smaller value of the gauge coupling at that scale. As a result, for any number of extra dimensions the exchange of the complete KK tower always gives a finite contribution. We show that (i) for d=1 the running of the gauge coupling decreases an 14% the effect of the KK modes on electroweak observables; (ii) in all cases more than 90% of the total effect comes from the excitations in the seven lowest KK levels and is then independent of ultraviolet physics.

hep-ph↗