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.Comment: 8 pages, to appear in Phys. Rev.

Production and propagation of heavy hadrons in air-shower simulators

Very energetic charm and bottom hadrons may be produced in the upper atmosphere when a primary cosmic ray or the leading hadron in an extensive air shower collide with a nucleon. At $E\approx 10^8$ GeV their decay length becomes of the order of 10 km, implying that they tend to interact in the air instead of decaying. Since the inelasticity in these collisions is much smaller than the one in proton and pion collisions, there could be rare events where a heavy-hadron component transports a significant amount of energy deep into the atmosphere. We have developed a module for the detailed simulation of these processes and have included it in a new version of the air shower simulator AIRES. We study the frequency, the energy distribution and the depth of charm and bottom production, as well as the depth and the energy distribution of these quarks when they decay. As an illustration, we consider the production and decay of tau leptons (from $D_s$ decays) and the lepton flux at PeV energies from a 30 EeV proton primary. The proper inclusion of charm and bottom hadrons in AIRES opens the possibility to search for air-shower observables that are sensitive to heavy quark effects.Comment: Accepted for publication in Astroparticle Physic

Leptophobic Z' from superstring derived models

It was recently suggested that the reported anomalies in R_b and R_c can be interpreted as the effect of a heavy vector boson that couples to quarks and is universally decoupled from leptons. We examine how an extra gauge boson with this property can arise from superstring derived models. In a specific three generation model we show that the U(1)_{B-L} symmetry combines with the horizontal flavor symmetries to form a universal leptophobic U(1) symmetry. In our model there is an enhancement of the color gauge group from twisted sectors. The enhancement occurs after the breaking of the unifying gauge symmetry by ``Wilson lines''. The leptophobic U(1) symmetry then becomes a generator of the color SU(4) gauge group. We examine how similar symmetries may appear in other string models without the enhancement. We propose that if the current LEP anomalies persist it may be evidence for a certain class of un--unified superstring models

Corte compensado del Pirineo oriental: Geometría de las cuencas de antepaís y edades de emplazamiento de los mantos de corrimiento

El manto del Pedraforca se ha dividido en dos unidades: el manto superior del Pedraforca predominantemente constituido por materiales del Cretácico inferior y el manto inferior del Pedraforca formado principalmente por una serie de Cretácico superior discordante por encima del Jurásico. La parte aflorante del manto superior del Pedraforca se ha interpretado como una rampa de bloque superior. Su edad de emplazamiento es Maastrichtiense terminal. La dirección de transporte N-S de los mantos, en especial del manto inferior del Pedraiorca puede deducirse de la disposición de sus rampas oblicuas con direcciones NNE-SSW y NW-SE. Estructuras frontales de dirección E-W pueden observarse en todo el manto. En el manto del Cadi, las estructuras tienen dirección E-W normal a la direccibn de transporte. El corte geológico se ha construido paralelamente a la dirección de transporte, a través de una zona en la cual no se presentan rampas oblicuas. El acortamiento minimo del Pirineo oriental es de 50 km para el conjunto de mantos. Esto representa el 68%. La velocidad media de desplazamiento del conjunto de mantos de corrimiento para esta zona del Pirineo fue de 1 mm/a., siendo 3.3. mm/a. la velocidad media establecida para el manto inferior del Pedraforca. La velocidad de migración de los depocentros aumenta hacia el antepaís, siendo 4.9 mm/a. la velocidad deducida para las secuencias deposicionales superiores (Milany-Solsona) de edad Bartoniense-0- ligoceso inferior

The lightest Higgs mass in supersymmetric models with extra dimensions

In the four-dimensional supersymmetric standard model extended with gauge singlets the lightest Higgs boson mass, $M_H$, has an important contribution proportional to the squared of the superpotential coupling $\lambda$ of singlets to Higgs fields, $\lambda SH_1\cdot H_2$. The requirement of perturbativity up to the unification scale yields an upper bound on $M_H\sim 140$ GeV. In extensions to theories with (longitudinal) extra dimensions at the TeV where such coupling exists and massive Kaluza-Klein states fall into N=2 representations, if either of the Higgs or singlet fields live in the bulk of the extra dimensions, the $\beta$-function of $\lambda$ is suppressed due to the absence of anomalous dimension of hypermultiplets to leading order. This implies a slower running of $\lambda$ and an enhancement of its low energy value. The $M_H$ upper bound increases to values $M_H\lesssim 165$ GeV.Comment: Latex2e, 11 pages, 1 figur

High-speed tunable photonic crystal fiber-based femtosecond soliton source without dispersion pre-compensation

We present a high-speed wavelength tunable photonic crystal fiber-based source capable of generating tunable femtosecond solitons in the infrared region. Through measurements and numerical simulation, we show that both the pulsewidth and the spectral width of the output pulses remain nearly constant over the entire tuning range from 860 to 1160 nm. This remarkable behavior is observed even when pump pulses are heavily chirped (7400 fs^2), which allows to avoid bulky compensation optics, or the use of another fiber, for dispersion compensation usually required by the tuning device.Comment: 8 pages, 11 figure