Gautam Rupak

Phase separation in asymmetrical fermion superfluids

Motivated by recent developments on cold atom traps and high density QCD we consider fermionic systems composed of two particle species with different densities. We argue that a mixed phase composed of normal and superfluid components is the energetically favored ground state. We suggest how this phase separation can be used as a probe of fermion superfluidity in atomic traps.

Low energy expansion in the three body system to all orders and the triton channel

Abstract We extend and systematise the power counting for the three-body system, in the context of the “pion-less” Effective Field Theory approach, to all orders in the low-energy expansion. We show that a sub-leading part of the three-body force appears at the third order and delineate how the expansion proceeds at higher orders. After discussing the renormalisation issues in a simple bosonic model, we compute the phase shifts for neutron–deuteron scattering in the doublet S wave (triton) channel and compare our results with phase shift analysis and potential model calculations.

Chiral perturbation theory for the Wilson lattice action

The authors extend chiral perturbation theory to include linear dependence on the lattice spacing a for the Wilson action. The perturbation theory is written as a double expansion in the small quark mass m{sub q} and lattice spacing a. They present formulae for the mass and decay constant of a flavor-non-singlet meson in this scheme to order a and m{sub q}{sup 2}. The extension to the partially quenched theory is also described.

Chiral perturbation theory at O(a**2) for lattice QCD

We construct chiral effective Lagrangian for two lattice theories: one with Wilson fermions and the other with Wilson sea fermions and Ginsparg-Wilson valence fermions. For each of these theories we construct the Symanzik action through

Precision calculation of np→dγ cross section for big-bang nucleosynthesis

\mathcal{O}{(a}^{2}).

Improving the convergence of NN effective field theory

The chiral Lagrangian is then derived, including terms of

Ab Initio Calculation of the Spectrum and Structure of

\mathcal{O}{(a}^{2}),

^{16}

which have not been calculated before. We find that there are only few new terms at this order. Corrections to existing coefficients in the continuum chiral Lagrangian are proportional to

O

{a}^{2}

Ab initio alpha–alpha scattering

and appear in the Lagrangian at