Kavli Affiliate: Ulrich Sperhake

| First 5 Authors: Roxana Rosca-Mead, Christopher J. Moore, Ulrich Sperhake, Michalis Agathos, Davide Gerosa

| Summary:

We compute families of spherically symmetric neutron-star models in

two-derivative scalar-tensor theories of gravity with a massive scalar field.

The numerical approach we present allows us to compute the resulting spacetimes

out to infinite radius using a relaxation algorithm on a compactified grid. We

discuss the structure of the weakly and strongly scalarized branches of

neutron-star models thus obtained and their dependence on the linear and

quadratic coupling parameters $alpha_0$, $beta_0$ between the scalar and

tensor sectors of the theory, as well as the scalar mass $mu$. For highly

negative values of $beta_0$, we encounter configurations resembling a

"gravitational atom", consisting of a highly compact baryon star surrounded by

a scalar cloud. A stability analysis based on binding-energ calculations

suggests that these configurations are unstable and we expect them to migrate

to models with radially decreasing baryon density {it and} scalar field

strength.

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