Bloom-Gilman duality of the nucleon structure function and the elastic peak contribution

The occurrence of the Bloom-Gilman duality in the nucleon structure function is investigated by analyzing the Q**2-behavior of low-order moments, both including and excluding the contribution arising from the nucleon elastic peak. The Natchmann definition of the moments has been adopted in order to cancel out target-mass effects. It is shown that the onset of the Bloom-Gilman duality occurs around Q**2 ~ 2 (GeV/c)**2 if only the inelastic part of the nucleon structure function is considered, whereas the inclusion of the nucleon elastic peak contribution leads to remarkable violations of the Bloom-Gilman duality.Comment: in Proc. of the XVI European Conference on Few-body Problems in Physics, Autrans (France), July 199

Nonlinear corrections to the DGLAP equations in view of the HERA data

The effects of the first nonlinear corrections to the DGLAP evolution equations are studied by using the recent HERA data for the structure function $F_2(x,Q^2)$ of the free proton and the parton distributions from CTEQ5L and CTEQ6L as a baseline. By requiring a good fit to the H1 data, we determine initial parton distributions at $Q_0^2=1.4$ GeV$^2$ for the nonlinear scale evolution. We show that the nonlinear corrections improve the agreement with the $F_2(x,Q^2)$ data in the region of $x\sim 3\cdot 10^{-5}$ and $Q^2\sim 1.5$ GeV$^2$ without paying the price of obtaining a worse agreement at larger values of $x$ and $Q^2$. For the gluon distribution the nonlinear effects are found to play an increasingly important role at x\lsim 10^{-3} and Q^2\lsim10 GeV$^2$, but rapidly vanish at larger values of $x$ and $Q^2$. Consequently, contrary to CTEQ6L, the obtained gluon distribution at $Q^2=1.4$ GeV$^2$ shows a power-like growth at small $x$. Relative to the CTEQ6L gluons, an enhancement up to a factor $\sim6$ at $x=10^{-5}$, $Q_0^2=1.4$ GeV$^2$ reduces to a negligible difference at Q^2\gsim 10 GeV$^2$.Comment: 13 pages, 5 eps-figures; revision: references added, Fig. 3 revise

Towards a Precise Parton Luminosity Determination at the CERN LHC

A new approach to determine the LHC luminosity is investigated. Instead of employing the proton-proton luminosity measurement, we suggest to measure directly the parton-parton luminosity. It is shown that the electron and muon pseudorapidity distributions, originating from the decay of W+, W- and Z0 bosons produced at 14 TeV pp collisions (LHC), constrain the x distributions of sea and valence quarks and antiquarks in the range from about 3 x 10**-4 to about 10**-1 at a Q**2 of about 10**4 GeV**2. Furthermore, it is demonstrated that, once the quark and antiquark structure functions are constrained from the W+,W- and Z0 production dynamics, other quark-antiquark related scattering processes at the LHC like q-qbar --> W+W- can be predicted accurately. Thus, the lepton pseudorapidity distributions provide the key to a precise parton luminosity monitor at the LHC, with accuracies of about +-1% compared to the so far considered goal of +-5%.Comment: plain tex, 14 pages, 5 figure

Electroweak instantons as a solution to the ultrahigh energy cosmic ray puzzle

We propose a scenario in which a simple power-like primary spectrum for protons with sources at cosmological distances leads to a quantitative description of all the details of the observed cosmic ray spectrum for energies from 10^{17} eV to 10^{21} eV. As usual, the ultrahigh energy protons with energies above E_{GZK} ~ 4 x 10^{19} eV loose a large fraction of their energies by the photoproduction of pions on the cosmic microwave background, which finally decay mainly into neutrinos. In our scenario, these so-called cosmogenic neutrinos interact with nucleons in the atmosphere through Standard Model electroweak instanton-induced processes and produce air showers which are hardly distinguishable from ordinary hadron-initiated air showers. In this way, they give rise to a second contribution to the observed cosmic ray spectrum -- in addition to the one from above mentioned protons -- which reaches beyond E_{GZK}. Since the whole observed spectrum is uniquely determined by a single primary injection spectrum, no fine tuning is needed to fix the ratio of the spectra below and above E_{GZK}. The statistical analysis shows an excellent goodness of this scenario. Possible tests of it range from observations at cosmic ray facilities and neutrino telescopes to searches for QCD instanton-induced processes at HERA.Comment: 14 pages, 7 figure

Black Holes at Neutrino Telescopes

In scenarios with extra dimensions and TeV-scale quantum gravity, black holes are expected to be produced in the collision of light particles at center-of-mass energies above the fundamental Planck scale with small impact parameters. Black hole production and evaporation may thus be studied in detail at the Large Hadron Collider (LHC). But even before the LHC starts operating, neutrino telescopes such as AMANDA/IceCube, ANTARES, Baikal, and RICE have an opportunity to search for black hole signatures. Black hole production in the scattering of ultrahigh energy cosmic neutrinos on nucleons in the ice or water may initiate cascades and through-going muons with distinct characteristics above the Standard Model rate. In this Letter, we investigate the sensitivity of neutrino telescopes to black hole production and compare it to the one expected at the Pierre Auger Observatory, an air shower array currently under construction, and at the LHC. We find that, already with the currently available data, AMANDA and RICE should be able to place sensible constraints in black hole production parameter space, which are competitive with the present ones from the air shower facilities Fly's Eye and AGASA. In the optimistic case that a ultrahigh energy cosmic neutrino flux significantly higher than the one expected from cosmic ray interactions with the cosmic microwave background radiation is realized in nature, one even has discovery potential for black holes at neutrino telescopes beyond the reach of LHC.Comment: 14 pages, 6 figure

Collider versus Cosmic Ray Sensitivity to Black Hole Production

In scenarios with extra dimensions and TeV-scale quantum gravity, black holes are expected to be produced copiously at center-of-mass energies above the fundamental Planck scale. The Large Hadron Collider (LHC) may thus turn into a factory of black holes, at which their production and evaporation may be studied in detail. But even before the LHC starts operating, the Pierre Auger Observatory for cosmic rays, presently under construction, has an opportunity to search for black hole signatures. Black hole production in the scattering of ultrahigh energy cosmic neutrinos on nucleons in the atmosphere may initiate quasi-horizontal air showers far above the Standard Model rate. In this letter, we compare the sensitivity of LHC and Auger to black hole production by studying their respective reach in black hole production parameter space. Moreover, we present constraints in this parameter space from the non-observation of horizontal showers by the Fly's Eye collaboration. We find that if the ultrahigh energy neutrino flux is at the level expected from cosmic ray interactions with the cosmic microwave background radiation, Auger has only a small window of opportunity to detect black holes before the start of the LHC. If, on the other hand, larger ultrahigh energy neutrino fluxes on the level of the upper limit from ``hidden'' hadronic astrophysical sources are realized in nature, then the first signs of black hole production may be observed at Auger. Moreover, in this case, the Fly's Eye constraints, although more model dependent, turn out to be competitive with other currently available constraints on TeV-scale gravity which are mainly based on interactions associated with Kaluza-Klein gravitons.Comment: 13 pages, 6 figures; references added and more emphasis on Fly's Eye constraints; version to appear in Phys. Lett.

Verifiable Model of Neutrino Masses from Large Extra Dimensions

We propose a new scenario of neutrino masses with a Higgs triplet $(\xi^{++},\xi^+,\xi^0)$ in a theory of large extra dimensions. Lepton number violation in a distant brane acts as the source of a very small trilinear coupling of $\xi$ to the standard Higgs doublet in our brane. Small realistic Majorana neutrino masses are \underline{naturally} obtained with the fundamental scale $M_* \sim {\cal O}(1)$ TeV, foretelling the possible discovery of $\xi$ (m_\xi\lsim M_*) at future colliders. Decays of $\xi^{++}$ into same-sign dileptons are fixed by the neutrino mass matrix. Observation of $\mu-e$ conversion in nuclei is predicted.Comment: A comment on Tevatron reach and two references added. Discussion and conclusions unchange

R-Parity Violation at HERA

We summarize the signals at HERA in supersymmetric models with explicitly broken R-parity. As the most promising case, we consider in detail the resonant production of single squarks through an operator $L_1Q_i{ \bar D}_j$, a production process analogous to that for leptoquarks. However, the dominant decay of the squark to a quark and a photino leads to a very different experimental signature. We examine in particular the case where the photino decays to a positron and two quarks. Using a detailed Monte-Carlo procedure we obtain a discovery limit in the squark mass---Yukawa coupling plane. HERA can discover a squark for a mass as large as 270 \gev and for an R-parity violating Yukawa coupling as small as $5.8 \times 10^{-3}$.Comment: 23 pages, 11 figures upon request, Oxford Preprint, OUNP-92-1

Orthogonal U(1)'s, Proton Stability and Extra Dimensions

In models with a low quantum gravity scale, one might expect that all operators consistent with gauge symmetries are present in the low-energy effective theory. If this is the case, some mechanism must be present to adequately suppress operators that violate baryon number. Here we explore the possibility that the desired suppression is a consequence of an additional, spontaneously-broken, non-anomalous U(1) symmetry that is orthogonal to hypercharge. We show that successful models can be constructed in which the additional particle content necessary to cancel anomalies is minimal, and compatible with the constraints from precision electroweak measurements and gauge unification. If unification is sacrificed, and only the new U(1) and its associated Higgs fields live in the bulk, it is possible that the gauge field zero mode and first few Kaluza-Klein excitations lie within the kinematic reach of the Tevatron. For gauge couplings not much smaller than that of hypercharge, we show that these highly leptophobic states could evade detection at Run I, but be discovered at Run II. Our scenario presents an alternative to the `cartographic' solution to baryon number violation in which leptons and quarks are separated in an extra dimension.Comment: 16 pages LaTeX, 4 figure