Bose-Einstein condensate strings

Harkó, Tiberiu; Lake, Matthew J.

doi:10.1103/physrevd.91.045012

Cited by 35 publications

(23 citation statements)

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“…This possibility has been intensively investigated in the literature (see [39] for a detailed discussion of the condensation processes in astrophysics), and the existence of stars with majority matter content in the form of a BEC cannot be excluded by present observations [40,41]. The matter inside a BEC star obeys a polytropic equation of state with polytropic index n = 1, and string-like objects composed of polytropic BEC matter, which resemble dark matter filaments, may also have formed in the early Universe [42]. For a class of self-gravitating matter models, with spherically symmetric field configurations, general scaling arguments were developed in [43,44] and applied to both the Einstein-Yang-Mills system and the Einstein sigma model.…”

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confidence: 86%

Mass bounds for compact spherically symmetric objects in generalized gravity theories

2016

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We derive upper and lower bounds on the mass-radius ratio of stable compact objects in extended gravity theories, in which modifications of the gravitational dynamics via-á-vis standard general relativity are described by an effective contribution to the matter energy-momentum tensor. Our results include the possibility of a variable coupling between the matter sector and the gravitational field and are valid for a large class of generalized gravity models. The generalized continuity and Tolman-Oppenheimer-Volkoff equations are expressed in terms of the effective mass, density and pressure, given by the bare values plus additional contributions from the total energy-momentum tensor, and general theoretical limits for the maximum and minimum mass-radius ratios are explicitly obtained. As applications of the formalism developed herein, we consider compact bosonic objects, described by scalar-tensor gravitational theories with self-interacting scalar field potentials, and charged compact objects, respectively. For Higgs type models, we find that these bounds can be expressed in terms of the value of the potential at the surface of the compact object. Minimizing the energy with respect to the radius, we obtain explicit upper and lower bounds on the mass, which admits a Chandrasekhar type representation. For charged compact objects, we consider the effects of the Poincaré stresses on the equilibrium structure and obtain bounds on the radial and tangential stresses. As a possible astrophysical test of our results, we obtain the general bound on the gravitational redshift for compact objects in extended gravity theories, and explicitly compute the redshift restrictions for objects with nonzero effective surface pressure. General implications of minimum mass bounds for the gravitational stability of fundamental particles and for the existence of holographic duality between bulk and boundary degrees of freedom are also considered.

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confidence: 86%

Mass bounds for compact spherically symmetric objects in generalized gravity theories

2016

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“…It also becomes important when some types of the topological effects are needed suddenly by assigning an independent metric. In the context of modified theories of gravity, cosmic strings are investigated in f (R) gravity [58,60], teleparallel theories [61][62][63], brane worlds [64], Kaluza-Klein models [65], Lovelock Lagrangians [66], Gauss-Bonnet [67][68][69], Born-Infeld [70,71], bimetric theories [72], non-relativistic models of gravity [73], scalar-tensor theories [74][75][76][77][78][79], Brans-Dicke theory [80][81][82][83][84][85], dilation gravity [86,87], non-minimally coupled models of gravity [88], Mimetic gravity [89] and, recently, in the Bose-Einstein condensate strings [90]. However, the cosmic string is still unexplored in gravity's rainbow setting.…”

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confidence: 99%

Cosmic string in gravity’s rainbow

Momeni

Upadhyay

Myrzakulov

et al. 2017

Astrophys Space Sci

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In this paper, we study the various cylindrical solutions (cosmic strings) in gravity's rainbow scenario. In particular, we calculate the gravitational field equations corresponding to energy-dependent background. Further, we discuss the possible Kasner, quasi-Kasner and non-Kasner exact solutions of the field equations. In this framework, we find that quasiKasner solutions can not be realized in gravity's rainbow. Assuming only time-dependent metric functions, we also analyse the time-dependent vacuum cosmic strings in gravity's rainbow, which are completely different than the other GR solutions. I. OVERVIEW AND MOTIVATIONA strong notion of an observer independent minimum length scale has been found in all theories of quantum gravity, for instance, in string theory [1], noncommutative geometry [2], loop quantum gravity [3,4] and Lorentzian dynamical triangulations [5][6][7][8]. Here we point out that the nascent GW astronomy [9] could help in discriminating among general relativity or alternative theories [10]. There is no harm to assume this minimum measurable length scale as the Planck scale. The mathematical ground of general theory of relativity is based on a smooth manifold which breaks down when energies of probe reaches the order of Planck energy [11,12].Keeping this point in mind, one may expect a radically new picture of spacetime, which includes departure from the standard relativistic dispersion relation. A departure from the standard dispersion relation indicates that the system incorporates a breaking of Lorentz invariance. * Electronic address:

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“…In [59], it was suggested that BoseEinstein condensates (BECs), consisting of axionic dark matter or cosmological scalar fields [60], may have condensed to form string-like objects on cosmic scales. Such objects are capable of fulfilling the role of dark matter filaments [61].…”

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confidence: 99%

Can Superconducting Cosmic Strings Piercing Seed Black Holes Generate Supermassive Black Holes in the Early Universe?

Lake

Harkó

2017

Fortschritte der Physik

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The discovery of a large number of supermassive black holes (SMBH) at redshifts z > 6, when the Universe was only 900 million years old, raises the question of how such massive compact objects could form in a cosmologically short time interval. Each of the standard scenarios proposed, involving rapid accretion of seed black holes or black hole mergers, faces severe theoretical difficulties in explaining the short-time formation of supermassive objects. In this work we propose an alternative scenario for the formation of SMBH in the early Universe, in which energy transfer from superconducting cosmic strings piercing small seed black holes is the main physical process leading to rapid mass increase. As a toy model, the accretion rate of a seed black hole pierced by two antipodal strings carrying constant current is considered. Using an effective action approach, which phenomenologically incorporates a large class of superconducting string models, we estimate the minimum current required to form SMBH with masses of order M = 2 × 10 9 M⊙ by z = 7.085. This corresponds to the mass of the central black hole powering the quasar ULAS J112001.48+064124.3 and is taken as a test case scenario for early-epoch SMBH formation. For GUT scale strings, the required fractional increase in the string energy density, due to the presence of the current, is of order 10 −7 , so that their existence remains consistent with current observational bounds on the string tension. In addition, we consider an "exotic" scenario, in which an SMBH is generated when a small seed black hole is pierced by a higher-dimensional F −string, predicted by string theory. We find that both topological defect strings and fundamental strings are able to carry currents large enough to generate early-epoch SMBH via our proposed mechanism.

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Bose-Einstein condensate strings

Cited by 35 publications

References 124 publications

Mass bounds for compact spherically symmetric objects in generalized gravity theories

Mass bounds for compact spherically symmetric objects in generalized gravity theories

Cosmic string in gravity’s rainbow

Can Superconducting Cosmic Strings Piercing Seed Black Holes Generate Supermassive Black Holes in the Early Universe?

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