LIMITS ON LONG-RANGE FIELDS DERIVED FROM BINARY RADIO PULSARS

Neutron stars, notably binary radio pulsars, are used to set limits on long-range scalar and vector fields. Such fields suggested by various particle physics models give rise to long-range forces in addition to gravity: a scalar attractive force and a vector repulsive force. It h as been argued that if the coupling strengths of the two forces are eq ual, they would cancel each other and would pass undetected in terrest rial and solar system experiments. Furthermore, it has been suggested that a vector with range comparable to a galactic scale combined with a scalar, of an equal strength but a much longer range, could explain flat galactic rotation curves without dark matter. In this paper we sh ow that the cancellation of the scalar and vector forces would not occ ur for gravitationally compact objects. The net force is larger, the l arger the specific binding energy. Thus, the mere existence of stably bound neutron stars provides a significant limit on the coupling stren gth of the fields to baryons. Stronger constraints are obtained from t iming data of binary radio pulsars. The orbital motion of the binary m embers results in an emission of radiation of the scalar and vector fi elds, which leads to a shortening of the orbital period. The dominant radiation terms are dipole, with the dipole moments larger, the larger the difference between the specific binding energies of the binary me mbers. This makes close binary radio pulsars with white dwarf companio ns ideal systems for testing such fields. We derive the rate of change of the orbital period resulting from this radiation and compare it to the timing data of two such pulsars: PSR 0665+64 and PSR 1855+09. We obtain that the coupling to baryon number is at most similar to 0.13 o f the gravitational coupling, and the coupling to lepton number is les s than similar to 0.02 of the gravitational coupling. The derived boun ds rule out the possibility that these fields could provide an alterna tive to dark matter.When the companion is a neutron star, as in PSR 19 13+16, the dipole moments are much smaller and are very sensitive to t he values of the masses of the binary members. In the presence of the additional fields, the mass values inferred from the measurements will depend on the coupling strength to baryon number. Allowing for the po ssibility that such a dependence will slightly decrease the difference between the two masses yields an upper limit on the strength of the c oupling to baryon number of similar to 0.45 of the gravitational coupl ing.