Extensions in FormCalc 5.3
We present a new tool for editing Feynman diagrams as well as several extensions in version 5.3 of the package FormCalc for the calculation of Feynman diagrams.
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arXiv subjects
J. I. Illana
Publications and source records attributed to J. I. Illana.
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.
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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.
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Excursions into FeynArts and FormCalc
Programming techniques which extend the capabilities of FeynArts and FormCalc are introduced and explained using examples from real applications.
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Interplay between Hbs and bsgamma in the MSSM with Non-Minimal Flavour Violation
We investigate the constraints on flavour-changing neutral heavy Higgs-boson decays H-> b \bar s from b -> s gamma bounds on the flavour-mixing parameters of the MSSM with non-minimal flavour violation (NMFV). In our analysis we include the contributions from the SM and new physics due to general flavour mixing in the squark mass matrices. We study the case of one and two non-zero flavour-mixing parameters and find that in the latter case the interference can raise the Higgs flavour-changing branching ratios by one or two orders of magnitude with respect to previous predictions based on a single non-zero parameter and in agreement with present constraints from $B$ physics. In the course of our work we developed a new "FeynArts" model file for the NMFV MSSM and added the necessary code for the evaluation to "FormCalc". Both extensions are publicly available.
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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.
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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.
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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.
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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.
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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.
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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.
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Top Dipole Form Factors and Loop-induced CP-violation in Supersymmetry
The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of the top quark are presented. Far from the Z peak, they are not sufficient to account for all the new physics effects. In the context of the calculation of the process e^+e^- -> t tbar to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.
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Dipole Form Factors and Loop-induced CP-violation in Supersymmetry
The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of heavy fermions are reviewed. For the $Z$ boson on shell, the weak-magnetic and weak-electric dipole moments of the $τ$ lepton and the $b$ quark can be defined and directly connected to observables. But far from the $Z$ peak, the weak and electromagnetic dipole form factors are not enough to account for all the new physics effects. In the context of the calculation of the process $e^+e^-\to t\bar{t}$ to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The set of tensor integrals employed, the one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.
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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.
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Charged Lepton Flavour Violation from Massive Neutrinos in Z Decays
Present evidences for neutrino masses and lepton flavour mixings allow to predict, in the Standard Model with light neutrinos, branching rates for the decays Z --> e mu, mu tau, e tau of less than 10^{-54}, while present experimental exclusion limits from LEP 1 are of order 10^{-5}. The GigaZ option of the TESLA Linear Collider project will extend the sensitivity down to about 10^{-8}. We study in a systematic way some minimal extensions of the Standard Model and show that GigaZ might well be sensitive to the rates predicted from these scenarios.
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Predictions for Z --> mu tau and Related Reactions
We discuss predictions for the lepton-flavour changing decays Z --> e mu, mu tau, e tau which may be searched for at the Giga-Z option of the Tesla Linear Collider project with Z resonance production rates as high as 10^9. We try to be as model-independent as possible and consider both the Dirac and Majorana mass cases. The Standard Model, if being minimally extended by the inclusion of light neutrino masses with some mixings as observed in neutrino oscillation search experiments, predicts completely negligible rates. With a more general neutrino content quite interesting expectations may be derived.
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Top-Quark Production and Decay in the MSSM
We review the features of top-quark decays and loop-induced effects in the production cross section and CP-violating observables of e+e- -> t t-bar which are specific to the R-parity conserving Minimal Supersymmetric Standard Model (MSSM).
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Dipole Moments in Supersymmetry
The one-loop MSSM contributions to the weak dipole moments of the τlepton and the b quark (at the Z peak) as well as the electromagnetic and weak dipole form factors of the t quark (at arbitrary s>4m^2_t) are reviewed. Emphasis is given to the relevance of the t-quark CP-violating weak and electric dipole form factors as a part of the full one-loop correction to the process e^+e^- --> t \bar{t} in the MSSM.
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