On the Effect of Nuclear Response Functions in Dark Matter Direct Detection

We examine the effect of nuclear response functions, as laid out in [Fitzpatrick et al, arXiv:1203.3542], on dark matter (DM) direct detection in the context of well-motivated UV completions, including electric and magnetic dipoles, anapole, spin-orbit, and pseudoscalar-mediated DM. Together, these encompass five of the six nuclear responses extracted from the non-relativistic effective theory of [Fitzpatrick et al, arXiv:1203.3542] (with the sixth difficult to UV complete), with two of the six combinations corresponding to standard spin-independent and -dependent responses. For constraints from existing direct detection experiments, we find that only the COUPP constraint, due to its heavy iodine target with large angular momentum and an unpaired spin, and its large energy range sensitivity, is substantially modified by the new responses compared to what would be inferred using the standard form factors to model the energy dependence of the response. For heavy targets such as xenon and germanium, the behavior of the new nuclear responses as recoil energy increases can be substantially different than that of the standard responses, but this has almost no impact on the constraints derived from experiments such as LUX, XENON100 and CDMS since the maximum nuclear recoil energy detected in these experiments is relatively low. We simulate mock data for 80 and 250 GeV DM candidates utilizing the new nuclear responses to highlight how they might affect a putative signal, and find the new responses are most important for momentum-suppressed interactions such as the magnetic dipole or pseudoscalar-mediated interaction when the target is relatively heavy (such as xenon and iodine).Comment: 42 pages, 12 figures, 5 table

Asymmetric Dark Stars and Neutron Star Stability

We consider gravitationally bound states of asymmetric dark matter (ADM stars), and the impact of ADM capture on the stability of neutron stars. We derive and interpret the equation of state for ADM with both attractive and repulsive interactions, and solve the Tolman-Oppenheimer-Volkoff equations to find equilibrium sequences and maximum masses of ADM stars. Gravitational wave searches can utilize our solutions to model exotic compact objects (ECOs). Our results for attractive interactions differ substantially from those in the literature, where fermionic ADM with attractive self-interactions was employed to destabilize neutron stars more effectively than non-interacting fermionic ADM. By contrast, we argue that fermionic ADM with an attractive force is no more effective in destabilizing neutron stars than fermionic ADM with no self-interactions.Comment: 9 pages plus 2 appendices (15 pages total), 7 figures, 1 tabl

Light Dark Matter Anomalies After LUX

We examine the consistency of light dark matter (DM) elastic scattering in CoGeNT, DAMA, and CDMS-Silicon in light of constraints from XENON, CDMS, LUX, PICASSO and COUPP. We consider a variety of operators that have been employed to reconcile anomalies with constraints, including anapole, magnetic dipole, momentum-dependent, and isospin-violating DM. We find that elastic scattering through these alternative operators does not substantially reduce the tension between the signals and the null constraints for operators where at least two of the three purported signals map onto a common space in the DM mass--scattering cross-section plane. Taking a choice of the scintillation efficiency that lies at the $-1 \sigma$ region of the Manzur et al measurement relieves tension between signals and the LUX constraint---in particular for a magnetic dipole interaction and a xenophobic interaction (though for the latter the signal regions do not substantially overlap). We also find that modest changes in the halo model does not alter this result. We conclude that, even relaxing the assumption about the type of elastic scattering interaction and taking a conservative choice for the scintillation efficiency, LUX and the results from other null experiments remain in tension with a light DM elastic scattering explanation of direct detection anomalies.Comment: 27 pages, 8 figures; v2: typos corrected, a few references added, and in the appendix: discussion of LUX analysis expanded and clarifications made on XENON100 analysi

On Models of New Physics for the Tevatron Top A_FB

CDF has observed a top forward-backward asymmetry discrepant with the Standard Model prediction at 3.4 \sigma. We analyze models that could generate the asymmetry, including flavor-violating W's, horizontal Z'_Hs, triplet and sextet diquarks, and axigluons. We consider the detailed predictions of these models for the invariant mass and rapidity distributions of the asymmetry at the parton level, comparing against the unfolded parton-level CDF results. While all models can reproduce the asymmetry with the appropriate choice of mass and couplings, it appears at first examination that the extracted parton-level invariant mass distribution for all models are in conflict with Tevatron observations. We show on closer examination, however, that t tbar events in Z'_H and W' models have considerably lower selection efficiencies in high invariant mass bins as compared to the Standard Model, so that W', Z'_H, and axigluon models can generate the observed asymmetry while being consistent with the total cross-section and invariant mass spectrum. Triplet and sextet models have greater difficulty producing the observed asymmetry while remaining consistent with the total cross-section and invariant mass distribution. To more directly match the models and the CDF results, we proceed to decay and reconstruct the tops, comparing our results against the "raw" CDF asymmetry and invariant mass distributions. We find that the models that successfully generate the corrected CDF asymmetry at the parton level reproduce very well the more finely binned uncorrected asymmetry. Finally, we discuss the early LHC reach for discovery of these models, based on our previous analysis [arXiv:1102.0018].Comment: 29 pages, 14 figures, 2 table

Nuclear Structure of Bound States of Asymmetric Dark Matter

Models of Asymmetric Dark Matter (ADM) with a sufficiently attractive and long-range force gives rise to stable bound objects, analogous to nuclei in the Standard Model, called nuggets. We study the properties of these nuggets and compute their profiles and binding energies. Our approach, applicable to both elementary and composite fermionic ADM, utilizes relativistic mean field theory, and allows a more systematic computation of nugget properties, over a wider range of sizes and force mediator masses, compared to previous literature. We identify three separate regimes of nugget property behavior corresponding to (1) non-relativistic and (2) relativistic constituents in a Coulomb-like limit, and (3) saturation in an anti-Coulomb limit when the nuggets are large compared to the force range. We provide analytical descriptions for nuggets in each regime. Through numerical calculations, we are able to confirm our analytic descriptions and also obtain smooth transitions for the nugget profiles between all three regimes. We also find that over a wide range of parameter space, the binding energy in the saturation limit is an ${\cal O}(1)$ fraction of the constituent's mass, significantly larger than expectations in the non-relativistic case. In a companion paper, we apply our results to synthesis of ADM nuggets in the early Universe.Comment: 20 pages, 8 figures, 1 appendi