Bracketing the direct detection exclusion plot for a WIMP of spin one half in non-relativistic effective theory

초록

Assuming a standard Maxwellian velocity distribution for the WIMPs in the halo of our Galaxy we use the null results of an exhaustive set of 9 direct detection experiments to calculate the maximal variation of the exclusion plot for each Wilson coefficient of the most general Galilean-invariant effective Hamiltonian for a WIMP of spin one half due to interferences. We consider 56 Wilson coefficients C-t(pn) and alpha(pn)(t) , for WIMP-proton and WIMP-neutron contact interactions O, and the corresponding long range interaction O, /2, parameterized by a massless propagator 1/2. For each coupling we provide a different exclusion plot when the following set of operators is allowed to interfere: proton-neutron, i.e. - or -; contact-contact or long range-long range, i.e. ,-, or ,-, ; contact- long range, i.e. , -, . For each of the 56 Wilson coefficients , and , and for the largest number of interfering operators the exclusion plot variation can reach 3 orders of magnitude and reduces to a factor as small as a few for the Wilson coefficients of the effective interactions where the WIMP couples to the nuclear spin, thanks to the combination of experiments using proton-odd and neutron-odd targets. Some of the conservative bounds require an extremely high level of cancellation, putting into question the reliability of the result. We analyze this issue in a systematic way, showing that it affects some of the couplings driven by the operators O-1, O-3, O-11, O-12 and O-15, especially when interferences among contact and long range interactions are considered.

키워드