Papers by Jared Greenwald
While magnetic fields are ubiquitous features of stellar systems, it is only relatively recently ... more While magnetic fields are ubiquitous features of stellar systems, it is only relatively recently that the evolution of compact objects such as neutron stars have been simulated using both general relativity and ideal magnetohydrodynamics. An important aspect of these simulations is beginning with physically reasonable initial data. To this end, we consider the problem of constructing equilibrium configurations of axisymmetric,
Physical Review D, 2013
We study gravitational collapse of a spherical fluid in nonrelativistic general covariant theory ... more We study gravitational collapse of a spherical fluid in nonrelativistic general covariant theory of the Hořava-Lifshitz gravity with the projectability condition and an arbitrary coupling constant λ, where |λ − 1| characterizes the deviation of the theory from general relativity in the infrared limit. The junction conditions across the surface of a collapsing star are derived under the (minimal) assumption that the junctions be mathematically meaningful in terms of distribution theory. When the collapsing star is made of a homogeneous and isotropic perfect fluid, and the external region is described by a stationary spacetime, the problem reduces to the matching of six independent conditions. If the perfect fluid is pressureless (a dust fluid), it is found that the matching is also possible. In particular, in the case λ = 1, the external spacetime is described by the Schwarzschild (anti-) de Sitter solution written in Painlevé-Gullstrand coordinates. In the case λ = 1, the external spacetime is static but not asymptotically flat. Our treatment can be easily generalized to other versions of Hořava-Lifshitz gravity or, more generally, to any theory of higher-order derivative gravity. PACS numbers: 04.60.-m; 98.80.Cq; 98.80.-k; 98.80.Bp 1 Although Israel's method was initially developed only for nonnull hypersurfaces, it was later generalized to the null hypersurface case [41]. For a recent review of this method, we refer to [42] and references therein.
Physical Review D, 2011
We systematically study black holes in the Horava-Lifshitz (HL) theory by following the kinematic... more We systematically study black holes in the Horava-Lifshitz (HL) theory by following the kinematic approach, in which a horizon is defined as the surface at which massless test particles are infinitely redshifted. Because of the nonrelativistic dispersion relations, the speed of light is unlimited, and test particles do not follow geodesics. As a result, there are significant differences in causal structures and black holes between general relativity (GR) and the HL theory. In particular, the horizon radii generically depend on the energies of test particles. Applying them to the spherical static vacuum solutions found recently in the nonrelativistic general covariant theory of gravity, we find that, for test particles with sufficiently high energy, the radius of the horizon can be made as small as desired, although the singularities can be seen in principle only by observers with infinitely high energy. In these studies, we pay particular attention to the global structures of the solutions, and find that, because of the foliation-preserving-diffeomorphism symmetry, Diff(M, F), they are quite different from the corresponding ones given in GR, even though the solutions are the same. In particular, the Diff(M, F) does not allow Penrose diagrams. Among those vacuum solutions, some give rise to the structures of the Einstein-Rosen bridge, in which two asymptotically flat regions are connected by a throat with a finite non-zero radius. We also study slowly rotating solutions in such a setup, and obtain all the solutions characterized by an arbitrary function A0(r). The case A0 = 0 reduces to the slowly rotating Kerr solution obtained in GR.
Physical Review D, 2010
We systematically study spherically symmetric static spacetimes filled with a fluid in the Horava... more We systematically study spherically symmetric static spacetimes filled with a fluid in the Horava-Lifshitz theory of gravity with the projectability condition, but without the detailed balance. We establish that when the spacetime is spatially Ricci flat the unique vacuum solution is the de Sitter Schwarzshcild solution, while when the spacetime has a nonzero constant curvature, there exist two different vacuum solutions; one is an (Einstein) static universe, and the other is a new spacetime. This latter spacetime is maximally symmetric and not flat. We find all the perfect fluid solutions for such spacetimes, in addition to a class of anisotropic fluid solutions of the spatially Ricci flat spacetimes. To construct spacetimes that represent stars, we investigate junction conditions across the surfaces of stars and obtain the general matching conditions with or without the presence of infinitely thin shells. It is remarkable that, in contrast to general relativity, the radial pressure of a star does not necessarily vanish on its surface even without the presence of a thin shell, due to the presence of high order derivative terms. Applying the junction conditions to our explicit solutions, we show that it is possible to match smoothly these solutions (all with nonzero radial pressures) to vacuum spacetimes without the presence of thin matter shells on the surfaces of stars.
Bulletin of the American Physical Society, 2007
We are conducting a systematic study of the phenomenological properties of models on the region o... more We are conducting a systematic study of the phenomenological properties of models on the region of the string landscape occupied by weak coupled heterotic strings in the free fermionic formalism. Specifically, we are examining the statistics of phenomenological ...
Modern Physics Letters A, 2013
Utilizing the Gauge Framework, software under development at Baylor University, we explicitly con... more Utilizing the Gauge Framework, software under development at Baylor University, we explicitly construct all layer 1 weakly coupled free fermionic heterotic string (WCFFHS) gauge models up to order 32 in four to ten large spacetime dimensions. These gauge models are well suited to large scale systematic surveys and, while they offer little phenomenologically, are useful for understanding the structure of the WCFFHS region of the string landscape. Herein we present the gauge groups statistics for this swath of the landscape for both supersymmetric and non-supersymmetric models.
Journal of Cosmology and Astroparticle Physics, 2010
We study spherically symmetric static spacetimes generally filled with an anisotropic fluid in th... more We study spherically symmetric static spacetimes generally filled with an anisotropic fluid in the nonrelativistic general covariant theory of gravity. In particular, we find that the vacuum solutions are not unique, and can be expressed in terms of the U (1) gauge field A. When solar system tests are considered, severe constraints on A are obtained, which seemingly pick up the Schwarzschild solution uniquely. In contrast to other versions of the Horava-Lifshitz theory, non-singular static stars made of a perfect fluid without heat flow can be constructed, due to the coupling of the fluid with the gauge field. These include the solutions with a constant pressure. We also study the general junction conditions across the surface of a star. In general, the conditions allow the existence of a thin matter shell on the surface. When applying these conditions to the perfect fluid solutions with the vacuum ones as describing their external spacetimes, we find explicitly the matching conditions in terms of the parameters appearing in the solutions. Such matching is possible even without the presence of a thin matter shell. PACS numbers: 04.60.-m; 98.80.Cq; 98.80.-k; 98.80.Bp
The European Physical Journal C, 2012
The discovery that the number of physically consistent string vacua is on the order of 10 500 has... more The discovery that the number of physically consistent string vacua is on the order of 10 500 has prompted several statistical studies of string phenomenology. Contained here is one such study that focuses on the Weakly Coupled Free Fermionic Heterotic String (WCFFHS) formalism. Presented are systematic extensions of the well-known NAHE (Nanopoulos, Antoniadis, Hagelin, Ellis) set of basis vectors, which have been shown to produce phenomenologically realistic models. Statistics related to the number of U (1)'s, the specific gauge groups and their factors, non-Abelian singlets, and spacetime supersymmetries (ST SUSYs) are discussed for the full range of models produced.
Uploads
Papers by Jared Greenwald