scholarly journals Cosmological evolution of cosmic strings with time-dependent tension

2005 ◽  
Vol 72 (4) ◽  
Author(s):  
Masahide Yamaguchi
Keyword(s):  
Cosmic Strings ◽  
Cosmological Evolution ◽  
Time Dependent

scholarly journals Cosmological evolution of semilocal string networks

2019 ◽  
Vol 377 (2161) ◽  
pp. 20190004
Author(s):  
A. Achúcarro ◽  
A. Avgoustidis ◽  
A. López-Eiguren ◽  
C. J. A. P. Martins ◽  
J. Urrestilla
Keyword(s):  
Time Evolution ◽  
Topological Defect ◽  
Cosmic Strings ◽  
Thermodynamic Description ◽  
New Physics ◽  
Cosmological Evolution ◽  
Length Scale ◽  
Closed Loops ◽  
Global Monopoles ◽  
String Networks

Semilocal strings—a particular limit of electroweak strings—are an interesting example of a stable non-topological defect whose properties resemble those of their topological cousins, the Abrikosov–Nielsen–Olesen vortices. There is, however, one important difference: a network of semilocal strings will contain segments. These are ‘dumbbells’ whose ends behave almost like global monopoles that are strongly attracted to one another. While closed loops of string will eventually shrink and disappear, the segments can either shrink or grow, and a cosmological network of semilocal strings will reach a scaling regime. We discuss attempts to find a ‘thermodynamic’ description of the cosmological evolution and scaling of a network of semilocal strings, by analogy with well-known descriptions for cosmic strings and for monopoles. We propose a model for the time evolution of an overall length scale and typical velocity for the network as well as for its segments, and some supporting (preliminary) numerical evidence. This article is part of a discussion meeting issue ‘Topological avatars of new physics’.

scholarly journals Doubleverse entanglement in third quantized non-minimally coupled varying constants cosmologies

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Adam Balcerzak ◽  
Konrad Marosek
Keyword(s):  
Perfect Fluid ◽  
Gravitational Constant ◽  
Cosmic Strings ◽  
Scalar Fields ◽  
Time Dependent ◽  
Speed Of Light ◽  
The Third ◽  
Varying Constants ◽  
Two Parameters ◽  
Varying Gravitational Constant

Abstract In this paper we consider a third quantized cosmological model with varying speed of light c and varying gravitational constant G both represented by non-minimally coupled scalar fields. The third quantization of such a model leads to a scenario of the doubleverse with the two components being quantum mechanically entangled. We calculate the two parameters describing the entanglement, namely: the energy and the entropy of entanglement where the latter appears to be a proper measure of the entanglement. We consider a possibility that the entanglement can manifests itself as an effective perfect fluid characterized by the time dependent barotropic index $$w_{eff}$$weff, which for some specific case corresponds to the fluid of cosmic strings. It seems that such an entanglement induced effective perfect fluid may generate significant backreaction effect at early times.

FRW viscous cosmology with inhomogeneous equation of state and future singularity

2015 ◽  
Vol 30 (29) ◽  
pp. 1550144 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut ◽  
V. G. Miskin
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Dynamical Equation ◽  
Cosmological Evolution ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Future Singularity ◽  
Big Rip ◽  
Dependent Parameter ◽  
The Universe

A universe media is considered as a bulk viscosity described by inhomogeneous equation of state (EOS) of the form [Formula: see text], where [Formula: see text] is a time-dependent parameter. A generalized dynamical equation for the scale factor of the universe is proposed to describe the cosmological evolution, in which we assume the bulk viscosity and time-dependent parameter [Formula: see text] are linear combination of two terms of the form: [Formula: see text] and [Formula: see text], i.e.[Formula: see text]one is constant and other is proportional to Hubble parameter [Formula: see text]. In this framework, we demonstrate that this model can be used to explain the dark energy dominated universe, and the inhomogeneous term of specific form introduced in EOS, may lead to three kinds of fates of cosmological evolution: no future singularity, big rip or Type[Formula: see text]III singularity as presented by [S. Nojiri and S. D. Odintsov, Phys. Rev. D 72, 023003 (2005)].

MILLIMETER AND RADIOASTRONOMICAL CONSTRAINTS ON THE COSMOLOGICAL EVOLUTION OF STRINGS

1991 ◽  
Vol 06 (09) ◽  
pp. 1591-1616 ◽  
Author(s):  
M. SIGNORE ◽  
N. SÁNCHEZ
Keyword(s):  
Chemical Potential ◽  
Background Radiation ◽  
Cosmic Strings ◽  
Cosmological Evolution ◽  
Millisecond Pulsar ◽  
Microwave Background ◽  
Compatibility Conditions ◽  
Upper Limits ◽  
Spatial Fluctuations ◽  
Microwave Background Radiation

We study and place constraints on cosmic strings and on their cosmological evolution with emphasis on the results of five measurements: (i) millisecond pulsar timings, (ii) binary pulsar timings, (iii) spatial fluctuations in the intensity of the cosmic microwave background radiation (MBR). For superconducting strings (hereafter SCS), we add two other results: the spectrum of the MBR in (iv) the Rayleigh-Jean side and in (v) the Wien side. We find compatibility conditions between these five results which constrain the string evolution parameters independently of any numerical simulation result. We compare and comment about the gravitational decay rate of fundamental quantum strings in D=4, which appears closely related to that of classical cosmic strings. The absence of distortion recently reported by COBE’s FIRAS experiment leads to the following upper limits on: (a) the comptonization parameter, y≤10−3; (b) the chemical potential due to SCS, μoscs≤0.5 10−3; (c) the electromagnetic radiation to gravitational radiation ratio, f≤2.3 10−2; (d) the string parameter: Gμ<10−6 for generic values of string evolution parameters, Gμ<10−7 for values derived from numerical simulations. The small value of f shows that the decay of SCS must be governed by gravitation. The latest PSR 1937+21 timing measurements and the preliminary COBE data converge to the same upper limits on Gμ. These limits continue to descend but the breaking point is not yet reached.

Time evolution of a warped cosmic string

2014 ◽  
Vol 23 (08) ◽  
pp. 1450066 ◽  
Author(s):  
Reinoud Jan Slagter
Keyword(s):  
Time Evolution ◽  
Cosmic String ◽  
Background Radiation ◽  
Cosmic Strings ◽  
Unit Length ◽  
High Energy ◽  
Time Dependent ◽  
Warp Factor ◽  
Dark Matter Candidate ◽  
Axially Symmetric

The time evolution of a self-gravitating U(1) cosmic string on a warped five-dimensional (5D) axially symmetric spacetime is numerically investigated. Although cosmic strings are theoretically predicted in four-dimensional (4D) general relativistic models, there is still no observational evidence of their existence. From recent observations of the cosmic microwave background (CMB), it is concluded that these cosmic strings cannot provide a satisfactory explanation for the bulk of density perturbations. They even could not survive inflation. It is conjectured that only in a 5D warped braneworld model there will be observable imprint of these so-called cosmic superstrings on the induced effective 4D brane metric for values of the symmetry breaking scale larger than the grand unified theory (GUT) values. The warp factor makes these strings consistent with the predicted mass per unit length on the brane. However, in a time-dependent setting, it seems that there is a wavelike energy–momentum transfer to infinity on the brane, a high-energy braneworld behavior. This in contrast to earlier results in approximation models. Evidence of this information from the bulk geometry could be found in the gravitational cosmic background radiation via gravitational wave energy–momentum affecting the brane evolution. Fluctuations of the brane when there is a U(1) gauge field present, are comparable with the proposed brane tension fluctuations, or branons, whose relic abundance can be a dark matter candidate. We briefly made a connection with the critical behavior at the threshold of black hole formation found by Choptuik several decades ago in self-gravitating time-dependent scalar field models. The critical distinction between dispersion of the scalar waves and singular behavior fade away when a time-dependent warp factor is present.

scholarly journals COSMOLOGICAL EVOLUTION IN A TYPE-0 STRING THEORY

2002 ◽  
Vol 17 (17) ◽  
pp. 2241-2265 ◽  
Author(s):  
G. A. DIAMANDIS ◽  
B. C. GEORGALAS ◽  
N. E. MAVROMATOS ◽  
E. PAPANTONOPOULOS ◽  
I. PAPPA
Keyword(s):  
String Theory ◽  
Big Bang ◽  
Cosmological Evolution ◽  
Time Dependent ◽  
String Solution ◽  
Brane Worlds ◽  
Fifth Dimension ◽  
Inflationary Phase ◽  
The Universe

We study the cosmological evolution of a type-0 string theory by employing non-criticality, which may be induced by fluctuations of the D3 brane worlds. We check the consistency of the approach to [Formula: see text] in the corresponding σ-model. The ten-dimensional theory is reduced to an effective four-dimensional model, with only time dependent fields. We show that the four-dimensional universe has an inflationary phase and graceful exit from it, while the other extra dimensions are stabilized to a constant value, with the fifth dimension much larger than the others. We pay particular attention to demonstrating the role of tachyonic matter in inducing these features. The universe asymptotes, for large times, to a nonaccelerating linearly-expanding universe with a time-dependent dilaton and a relaxing to zero vacuum energy a lá quintessence. Our perturbative string solution appears to have initial singularities (Big Bang type), which however, we believe, may be lifted in a nonperturbative way, and they do not represent true singularities of the string theory.

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