148 research outputs found
Past-directed scalar field gradients and scalar-tensor thermodynamics
We refine and slightly enlarge the recently proposed first-order
thermodynamics of scalar-tensor gravity to include gravitational scalar fields
with timelike and past-directed gradients. The implications and subtleties
arising in this situation are discussed and an exact cosmological solution of
scalar-tensor theory in first-order thermodynamics is revisited in light of
these results.Comment: 7 pages, no figure
Spherical inhomogeneous solutions of Einstein and scalar-tensor gravity: a map of the land
We review spherical and inhomogeneous analytic solutions of the field
equations of Einstein and of scalar-tensor gravity, including Brans-Dicke
theory, non-minimally (possibly conformally) coupled scalar fields, Horndeski,
and beyond Horndeski/DHOST gravity. The zoo includes both static and dynamic
solutions, asymptotically flat, and asymptotically
Friedmann-Lema\^itre-Robertson-Walker ones. We minimize overlap with existing
books and reviews and we place emphasis on scalar field spacetimes and on
geometries that are "general" within certain classes. Relations between various
solutions, which have largely emerged during the last decade, are pointed out.Comment: 140 pages, one figure. Explanation text and bibliography expanded,
typographical errors corrected. Matches version to appear in Physics Report
New time-dependent solutions of viable Horndeski gravity
We generate new spherical and time-dependent solutions of viable Horndeski
gravity by disforming a solution of the Einstein equations with scalar field
source and positive cosmological constant. They describe dynamical objects
embedded in asymptotically FLRW spacetimes and contain apparent horizons and a
finite radius singularity that evolve in time in peculiar ways apparently not
encountered before in Einstein and "old" scalar-tensor gravity.Comment: 17 pages, 2 figure
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