Phenomenological aspects of scalar fields in astrophysics, cosmology and particle physics

Specific phenomenological consequences of scalar fields in the standard model of elementary particle physics and in the Brans-Dicke scalar-tensor theory of gravity are investigated. Calculation of the effective potential of the Higgs scalar in the standard model shows that for a top quark mass above 86 GeV, a stringent lower bound on the mass of the Higgs boson arises from the requirement of vacuum stability. With the help of a simplified model of cosmic ray collisions, it is argued that even very long-lived false vacuum states would have decayed through quantum tunneling induced by those collisions. The rate of change of the orbital period of very close binary systems such as the Binary Pulsar or the 11-minute binary 4U1820-30 due to the emission of gravitational radiation is analyzed. Observations of orbital period changes in such systems may give constraints on the strength of the coupling of the scalar field to the metric in Brans-Dicke theory that could be comparable to or even exceed results from solar-system based experiments. These bounds can be extended to massive Brans-Dicke type scalar fields, as long as their range is larger than the wave-zone of the binary system.