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Universe, Volume 5, Issue 7

July 2019 - 19 articles

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Cover Story: The Highly Eccentric Relativity Orbiter (HERO) is a space-based mission concept which aims to perform several tests of post-Newtonian (pN) gravity with a preferably drag-free spacecraft in a highly elliptical orbit. HERO may detect, for the first time, the pN linear trend of the semimajor axis a induced by the Earth's quadrupole, amounting to ≃4–12 cm yr−1 for certain orbital configurations. The secular decay of a of a geodetic satellite was recently measured with an error of 0.7 cm yr−1. Also, the pN Lense-Thirring and Schwarzschild effects could be accurately tested, depending on the drag-free apparatus. Moreover, the large orbital eccentricity would allow one to constrain several modified models of gravity and to measure the gravitational redshift with improved accuracy as well. View this paper.

Articles (19)

  • Review
  • Open Access
22 Citations
4,520 Views
38 Pages

When light from a distant source object, like a galaxy or a supernova, travels towards us, it is deflected by massive objects that lie in its path. When the mass density of the deflecting object exceeds a certain threshold, multiple, highly distorted...

  • Article
  • Open Access
11 Citations
3,444 Views
30 Pages

Do mass extinctions affect the development of intelligence? If so, we may expect to be in a universe that is exceptionally placid. We consider the effects of impacts, supervolcanoes, global glaciations, and nearby gamma ray bursts, and how their rate...

  • Communication
  • Open Access
4 Citations
3,010 Views
11 Pages

Compact Star Properties from an Extended Linear Sigma Model

  • János Takátsy,
  • Péter Kovács,
  • Zsolt Szép and
  • György Wolf

The equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations of compact stars. Using the equation of state given by the (axial-)vector meson extend...

  • Article
  • Open Access
469 Citations
10,590 Views
17 Pages

The Geometrical Trinity of Gravity

  • Jose Beltrán Jiménez,
  • Lavinia Heisenberg and
  • Tomi S. Koivisto

The geometrical nature of gravity emerges from the universality dictated by the equivalence principle. In the usual formulation of General Relativity, the geometrisation of the gravitational interaction is performed in terms of the spacetime curvatur...

  • Article
  • Open Access
12 Citations
4,355 Views
29 Pages

In a multiverse context, determining the probability of being in our particular universe depends on estimating its overall habitability compared to other universes with different values of the fundamental constants. One of the most important factors...

  • Review
  • Open Access
4 Citations
6,790 Views
21 Pages

This paper evaluates some important aspects of the multiverse concept. Firstly, the most realistic opportunity for it which is the spacetime variability of the physical constants and may deliver worlds with different physics, hopefully fulfilling the...

  • Article
  • Open Access
10 Citations
4,665 Views
40 Pages

We use the method of the Lewis-Riesenfeld invariant to analyze the dynamical properties of the Mukhanov-Sasaki Hamiltonian and, following this approach, investigate whether we can obtain possible candidates for initial states in the context of inflat...

  • Article
  • Open Access
17 Citations
3,868 Views
17 Pages

Phases of Hadron-Quark Matter in (Proto) Neutron Stars

  • Fridolin Weber,
  • Delaney Farrell,
  • William M. Spinella,
  • Germán Malfatti,
  • Milva G. Orsaria,
  • Gustavo A. Contrera and
  • Ian Maloney

In the first part of this paper, we investigate the possible existence of a structured hadron-quark mixed phase in the cores of neutron stars. This phase, referred to as the hadron-quark pasta phase, consists of spherical blob, rod, and slab rare pha...

  • Communication
  • Open Access
25 Citations
2,678 Views
6 Pages

The General Linear Cartan Khronon

  • Tomi Koivisto,
  • Manuel Hohmann and
  • Tom Złośnik

A Cartan geometry of the General Linear symmetry is formulated by dividing out the displacements from the group. The resulting action is quadratic in curvature, polynomial in all the (minimal) variables, and describes an observer space that—in...

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