There is accumulating evidence that (fundamental) scalar fields may exist in nature. The gravitational collapse of such a boson cloud would lead to a boson star (BS) as a new type of a compact object. As with white dwarfs and neutron stars, a limiting mass exists similarly, below which a BS is stable against complete gravitational collapse to a black hole. According to the form of the self-interaction of the basic constituents and spacetime symmetry, we can distinguish mini-, axidilaton, soliton, charged, oscillating and rotating BSs. Their compactness prevents a Newtonian approximation; however, modifications of general relativity, as in the case of Jordan?Brans?Dicke theory as a low-energy limit of strings, would provide them with gravitational memory. In general, a BS is a compact, completely regular configuration with structured layers due to the anisotropy of scalar matter, an exponentially decreasing 'halo', a critical mass inversely proportional to the constituent mass, an effective radius and a large particle number. Due to the Heisenberg principle, a completely stable branch exists, and as a coherent state, it allows for rotating solutions with quantized angular momentum. In this review, we concentrate on the fascinating possibilities of detecting the various subtypes of (excited) BSs: possible signals include gravitational redshift and (micro-)lensing, emission of gravitational waves, or, in the case of a giant BS, its dark matter contribution to the rotation curves of galactic halos.

https://iopscience.iop.org/article/10.1088/0264-9381/20/20/201/pdf

General relativistic boson stars

Reaction dynamics with exotic nuclei

Negative heat capacity in the critical region of nuclear fragmentation: an experimental evidence of the liquid-gas phase transition

Nuclear multifragmentation and phase transition for hot nuclei

Fluctuations and dynamical instabilities in heavy-ion reactions

Experimental data obtained with the 4{pi} multidetector system INDRA are used to study the light charged particle (LCP, Z{le}2) and intermediate mass fragment (IMF, Z{ge}3) production in peripheral and semicentral collisions of Xe and Sn at 50 MeV/nucleon. It is found that a sizable fraction of the detected LCP`s and IMF`s originates from the midvelocity region. These fragments can be seen to come either from a prompt (preequilibrium) mechanism or from a slower but dynamically influenced emission process. The relative magnitude of the dynamically influenced emission relative to the isotropic statistical evaporation is presented as a function of the transverse energy of light particles, used as an impact parameter selector. The results are compared to dynamical models with which a good agreement is obtained. {copyright} {ital 1997} {ital The American Physical Society}

S. Germain

Papers

Dynamical effects and intermediate mass fragment production in peripheral and semicentral collisions of Xe+Sn at 50 MeV/nucleon