Effects Of Isospin Asymmetric Nuclear Matter EoS On The Detection Of Dark Matter

The possible existence of dark matter?DM?is one of the most intriguing aspects of mod-ern particle physics,astrophysics and cosmology.In order to survey the nature of DM,a num-ber of observations and experiments have been conducted or are underway around the world.The most recent cosmological results based on Planck measurements of the cosmic microwave background?CMB?temperature and lensing-potential power spectra indicate that DM com-prises about 27%of the energy density of the Universe.The particle dark matter hypothesis can be tested via four processes:the production at particle accelerators,indirectly by searching for signals from annihilation products,directly via scattering on target nuclei,or detected from some other processes.In terrestrial laboratory,a number of underground DM direct detection experiments have been performed,and among them an excess of events over the expected back-ground has been observed by DAMA-Libra as well as some other experiments.However,these results are in strong tension with the constraints set by some other experimental groups,leaving a confusing situation for the community.This has led to a number of attempts trying to explain the discrepancy,among them the precise determination of the equation of state?EOS?of isospin asymmetric nuclear matter is ex-tremely useful for the detection of DM.Especially for the isospin-violating dark matter?IVDM?which provides a possible mechanism to ameliorate the tension among recent direct detection experiments,we demonstrate that the results of direct detection experiments based on neutron-rich target nuclei may depend strongly on the density dependence of the symmetry energy in the equation of state of isospin asymmetric nuclear matter which is presently largely unknown and controls the neutron skin thickness that reflects the relative difference of neutron and proton form factors in the neutron-rich nuclei.In particular,using the neutron and proton form factors obtained from Skyrme-Hartree-Fock calculations by varying the symmetry energy within the uncertainty region set by the latest model-independent measurement of the neutron skin thick-ness of²⁰⁸Pb from PREX experiment at JLab,we find that,for IVDM with neutron-to-proton coupling ratio fixed to f_n/f_p=-0.7,the form factor effect may enhance the sensitivity of Xe-based detectors?e.g.,XENON100 and LUX?to the DM-proton cross section by a factor of 3 in the DM mass region constrained by CMDS-II?Si?and even by more than an order of magnitude for heavy DM with mass larger than 80 GeV,compared with the results using the empirical Helm form factor.On the other hand,by assuming DM is non-interacting bosonic asymmetric IVDM,we investigate how the existence of old neutron stars limits the DM-proton scattering cross-section?_p,especially the effects of the isospin violating DM-nucleon interactions and the symmetry energy.We find that,the?_pbounds from old neutron stars can be varied by more than an or-der of magnitude depending on the specific values of the DM neutron-to-proton coupling ratio f_n/f_p,and they can be further varied by more than a factor of two depending on the density dependence of the symmetry energy.In particular,we demonstrate that the observed nearby isolated old neutron star PSR B1257+12 can set a very strong limit on?_pfor low-mass DM par-ticles??20 GeV?that reaches a sensitivity beyond the current best limits from direct detection experiments and disfavors the DM interpretation of previously-reported positive experimental results,including the IVDM.Finally,if the observed compact stars are old strange quark stars?SQSs?rather than neu-tron stars,important limits on the scattering cross sections between the light quarks and the non-interacting scalar dark matter can be set.After converting these limits into the DM-proton scattering cross sections based on the effective operator analyses,we find the resulting?_plimit from the old SQSs could be comparable with that of the current direct detection experiments but much weaker?by several orders of magnitude?than that obtained from the old neutron stars?NSs?,which requires an extremely small?_pfar beyond the limits of direct detection experi-ments.Our findings imply that the old pulsars are favored to be SQSs rather than NSs if that scalar DM was observed by future terrestrial experiments.