Sukanta Panda

Extra dimensions and strong neutrino-nucleon interactions above 1019 eV: breaking the GZK barrier

Abstract Cosmic ray events above 1020 eV are on the verge of confronting fundamental particle physics. The neutrino is the only candidate primary among established particles capable of crossing 100 Mpc intergalactic distances unimpeded. The magnitude of νN cross sections indicated by events, plus consistency with the Standard Model at low-energy, point to new physics of massive spin-2 exchange. In models based on extra dimensions, we find that the νN cross section rises to typical hadronic values of between 1 and 100 mb at energies above 1020 eV. Our calculations take into account constraints of unitarity. We conclude that air-showers observed with energies above 1019 eV are consistent with neutrino primaries and extra-dimension models. An upper bound of 1–10 TeV on the mass scale at which graviton exchange becomes strong in current Kaluza–Klein models follows.

Brane production and the neutrino nucleon cross-section at ultrahigh-energies in low scale gravity models

The observed ultrahigh energy cosmic rays (UHECR) might require a modification of the basic laws of physics. In low scale gravity models, where the neutrino–nucleon cross section rises to typical hadronic values at energies above 1020 eV, the neutrino becomes a candidate for the primary that initiates these showers. We calculate the neutrino–nucleon cross section at ultrahigh energies by assuming that it is dominated by the production of p-branes. We show, using a generalized Randall–Sundrum model, that the neutrino–nucleon cross-section at neutrino energies of 1020 eV is of the order of 100 mb, which is required for explaining the UHECR events. Similar results also follow in other models such as the Lykken–Randall model.

Electromagnetic polarization effects due to axion-photon mixing

We investigate the effect of axions on the polarization of electromagnetic waves as they propagate through astronomical distances. We analyze the change in the dispersion of the electromagnetic wave due to its mixing with axions. We find that this leads to a shift in polarization and turns out to be the dominant effect for a wide range of frequencies. We analyze whether this effect or the decay of photons into axions can explain the large scale anisotropies which have been observed in the polarizations of quasars and radio galaxies. We also comment on the possibility that the axion-photon mixing can explain the dimming of distant supernovae.

ROTATING BRANE WORLD BLACK HOLES

A five-dimensional rotating black string in a Randall–Sundrum brane world is considered. The black string intercepts the three-brane in a four-dimensional rotating black hole. The geodesic equations and the asymptotics in this background are discussed.

Two graviton production at e+e− and hadron hadron colliders in the Randall-Sundrum model

We compute the pair production cross section of two Kaluza Klein modes in the Randall-Sundrum model at e+e− and hadron hadron colliders. These processes are interesting because they get dominant contribution from the graviton interaction at next to leading order. Hence they provide a nontrivial test of the low scale gravity models. All the Feynman rules at next to leading order are also presented. These rules may be useful for many phenomenological applications including the computation of higher order loop corrections.

Curvature Singularity in f(R) Theories of Gravity

Although

Quantum treatment of the Weyl vector meson

f(R)

GÖDEL TYPE METRICS IN RANDALL SUNDRUM MODEL

modification of late time cosmology is successful in explaining present cosmic acceleration, it is difficult to satisfy the fifth-force constraint simultaneously. Even when the fifth-force constraint is satisfied, the effective scalar degree of freedom may move to a point (close to its potential minima) in the field space where the Ricci scalar diverges. We elucidate this point further with a specific example of

Black holes in brane worlds

f(R)

A new f(R) model in the light of local gravity test and late-time cosmology

gravity that incorporates several viable