Constraining the Randall-Sundrum Model Using Diphoton Production at Hadron Colliders

Virtual effects of gravitons in the production of diphotons at the upgraded Tevatron and at the LHC are analysed with the idea of probing the parameter space of the Randall-Sundrum (RS) model. It is shown that this process yields stringent constraints on the parameter space of the RS model. We show that data on diphoton production from Tevatron Run II will be sensitive to a masses of the first graviton resonance in the range of 700-1150 GeV, while at LHC the mass range probed will be in the region of 3.5 -- 5.5 TeV.Comment: 8 pages, Latex file + 1 ps figur

Charmonium Production at the LHC

The analyses of large transverse momentum charmonium production at the Tevatron have shown that fragmentation of gluons is an important production mechanism. We study large-$p_T$ charmonium production in $pp$ collisions at the LHC, and find that due to the copious gluon production at this energy, the gluon fragmentation contribution completely overwhelms the fusion contribution and the charm quark fragmentation contribution. Our analysis shows that for $J/\psi$ production at the LHC, there is a significant event rate even for $p_T \sim$~100~GeV. The measurement of the cross-section at such large values of $p_T$ will provide a very important test of the fragmentation mechanism.Comment: 9 pages including 2 postscript figure

Lh_c

The production cross-section of h_c, the 1P_1 charmonium state, can be predicted in Non-Relativistic QCD (NRQCD) using heavy-quark symmetry. We show that at the Large Hadron Collider a large cross-section for this resonance is predicted and it should be possible to look for the h_c through it decay into J/psi +pi even with the statistics that will be achieved within a few months of run-time at the LHC.Comment: 11 pages, LaTeX, 4 figures include

The shear dynamo problem for small magnetic Reynolds numbers

We study large-scale dynamo action due to turbulence in the presence of a linear shear flow, in the low conductivity limit. Our treatment is nonperturbative in the shear strength and makes systematic use of both the shearing coordinate transformation and the Galilean invariance of the linear shear flow. The velocity fluctuations are assumed to have low magnetic Reynolds number (Rm) but could have arbitrary fluid Reynolds number. The magnetic fluctuations are determined to lowest order in Rm by explicit calculation of the resistive Green's function for the linear shear flow. The mean electromotive force is calculated and an integro-differential equation is derived for the time evolution of the mean magnetic field. In this equation, velocity fluctuations contribute to two different kinds of terms, the C and D terms, in which first and second spatial derivatives of the mean magnetic field, respectively, appear inside the spacetime integrals. The contribution of the D terms is such that the time evolution of the cross-shear components of the mean field do not depend on any other components excepting themselves. Therefore, to lowest order in Rm but to all orders in the shear strength, the D terms cannot give rise to a shear-current assisted dynamo effect. Casting the integro-differential equation in Fourier space, we show that the normal modes of the theory are a set of shearing waves, labelled by their sheared wavevectors. The integral kernels are expressed in terms of the velocity spectrum tensor, which is the fundamental quantity that needs to be specified to complete the integro-differential equation description of the time evolution of the mean magnetic field.Comment: Near-final version; Accepted for publication in the Journal of Fluid Mechanics; References added; 22 pages, 2 figure

QCD calculation of J/psi+gamma mass distributions

We compute the J/psi+gamma invariant-mass distributions from the QCD subprocess g + g --> J/psi+gamma. At large masses, this subprocess is the dominant mechanism for J/psi+gamma production, and data could provide a good test of QCD. The mass distribution peaks at relatively small masses (3.4 - 4.0 GeV) and the subprocess could, therefore, represent a significant QCD background to J/psi+gamma decay of heavier charmonia. We also analyze the J/psi angular distribution in the J/psi+gamma rest frame.Comment: 7 pages LaTex, 4 figures available on request. CERN-TH.6974/93, ANL-HEP-PR-93.6

Non-perturbative unification in the light of LEP results

We consider an alternative to conventional GUTs originally proposed by Maiani, Parisi and Petronzio, where owing to the existence of extra fermion generations at some intermediate scale, the gauge couplings become large at high energies. We first comment on how the non- supersymmetric version of this scenario is ruled out; we then consider the two-loop evolution of the couplings in the supersymmetric extension of this scenario, and check whether such a scenario is feasible in the light of the precies values of couplings now available from LEP.Comment: Latex file 7 pages+1 fig. (ps file appended after the latex file), CERN-TH.6913/9