arXiv subjects
Publications and source records attributed to Namit Mahajan.
We study polarized cross-sections and forward-backward asymmetry for the process $e^+e-\to τ^+τ^-$ in the stabilized Randall-Sundrum scenario. It is shown that there is substantial deviation from the Standard Model predictions, both in terms of the actual numerical values and angular distributions.
A new mechanism is proposed for generating neutrino masses radiatively through a non-minimal coupling to gravity of fermionic bilinears involving massive neutral fermions. Such coupling terms can arise in theories where the gravity sector is augmented by a scalar field. They necessarily violate the principle of equivalence, but such violations are not ruled out by present experiments. It is shown that the proposed mechanism is realised most convincingly in theories of the Randall- Sundrum type, where gravity couples strongly in the TeV range. The mechanism has the potential for solving both the solar and atmospheric neutrino problems. The smallness of neutrino masses in this scenario is due to the fact that the interaction of the massive neutral fermions arises entirely from higher-dimensional operators in the effective Lagrangian.
Recently proposed stabilization mechanism of the Randall-Sundrum metric gives rise to a scalar radion, which couples universally to matter with a weak interaction ($\simeq 1$ TeV) scale. Demanding that gauge boson scattering as described by the effective low enerrgy theory be unitary upto a given scale leads to significant constraints on the mass of such a radion.
In the stabilised Randall-Sundrum brane world scenario, the radion can have phenomenologically testable effects, which can be measured against precisely measured electroweak physics data. We investigate the effect of two loop radion corrections to $K_L$ - $K_S$ mass difference to set a bound on the radion mass and vacuum expectation value. It is found that the leading two loop corrections are of the order $[Log(\frac{Λ^2}{m_ϕ^2}) ]^2$ where $Λ$ is the cut-off scale ${\cal O}(\sim$TeV) and $m_ϕ$ is the radion mass.
We study $γγ$ scattering in noncommutative QED (NCQED) where the gauge field has Yang-Mills type coupling, giving new contributions to the scattering process and making it possible for it to occur at tree level. The process takes place at one loop level in the Standard Model (SM) and could be an important signal for physics beyond SM. But it is found that the Standard Model contribution far exceeds the tree level contribution of the noncommutative case.
If the neutrinos are to be identified with the primary source of ultra-high energy cosmic rays(UHECR), their interaction on relic neutrinos is of great importance in understanding their long intergalactic journey. In theories with large compact dimensions, the exchange of a tower of massive spin-2 gravitons (Kaluza-Klein excitations) gives extra contribution to $ν\barν \longrightarrow f\bar{f}$ and $γγ$ processes along with the opening of a new channel for the neutrinos to annihilate with the relic cosmic neutrino background $ν\barν \longrightarrow G_{kk}$ to produce bulk gravitons in the extra dimensions. This will affect their attenuation. We compute the contribution of these Kaluza-Klein excitations to the above processes and find that for parameters of the theory constrained by supernova cooling, the contribution does indeed become the dominant contribution above $\sqrt{s} \simeq 300$ GeV.