PERTURBATIONS FROM D-TERM INFLATION

2007 ◽  
Vol 22 (25n28) ◽  
pp. 2035-2038
Author(s):  
OSAMU SETO ◽  
JUN'ICHI YOKOYAMA
Keyword(s):  
Spectral Index ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Unit Length ◽  
Higher Order ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
String Problem ◽  
Kähler Potential ◽  
Higher Order Corrections

We investigated a simple D-term inflation with taking account of higher order corrections in the Kähler potential. These terms may solve the cosmic string problem in D-term inflation model. The mass per unit length of cosmic strings formed after inflation can be suppressed enough. In addition, the change of the potential slope leads simultaneously a more tilted scalar spectral index ns ≃ 0.96 – 0.97 than that in the model without these corrections.

Smooth hybrid inflation on brane constrained by Planck data

2014 ◽  
Vol 29 (26) ◽  
pp. 1450146 ◽  
Author(s):  
M. Ferricha-Alami ◽  
H. Chakir ◽  
J. Inchaouh ◽  
M. Bennai
Keyword(s):  
Spectral Index ◽  
Index Formula ◽  
Type Ii ◽  
Planck Data ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
Central Value ◽  
Hybrid Inflation ◽  
Kähler Potential ◽  
Braneworld Model

It is shown that, in the supersymmetric smooth hybrid inflation model with the minimal Kähler potential, the spectral index ns is larger than 0.97 in the standard inflation. In this context, we study the smooth hybrid inflationary model in the framework of the Randall–Sundrum type-II braneworld model. We derive all known inflationary spectrum parameters which are widely consistent with Planck data for a particular choice of brane tension values λ especially for number of e-folds N = 50. We reproduce the central value of the scalar spectral index ns = 0.96 whereas the ratio r~(10-4-10-3). However, the running of the scalar spectral index [Formula: see text] is not excluded from the range given by the latest observational measurements.

New constraint of an attractor GL model in braneworld context

2017 ◽  
Vol 32 (19n20) ◽  
pp. 1750119
Author(s):  
Z. Mounzi ◽  
A. Safsafi ◽  
M. Ferricha-Alami ◽  
M. Bennai
Keyword(s):  
Power Spectrum ◽  
Spectral Index ◽  
Index Formula ◽  
Brane Tension ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
Central Value ◽  
Braneworld Model ◽  
Inflationary Parameters

We are interested in studying the generalization of the first chaotic inflation model in supergravity, which was proposed by Goncharov and Linde (GL model) and was recently revisited, in the framework of the Randall–Sundrum type 2 braneworld model. This model predicts a tiny ratio [Formula: see text] and [Formula: see text]. Our scenario predicts a great tensor-to-scalar ratio [Formula: see text] of the order [Formula: see text] and the central value of the scalar spectral index [Formula: see text] for a particular choice of values of brane tension [Formula: see text] and the parameter [Formula: see text]. We have shown that this scenario reproduces successfully an attractor behavior. We have also derived all known spectrum inflationary parameters, in particular the running [Formula: see text] and the power spectrum of the curvature perturbations [Formula: see text] which are widely consistent with Planck observations.

EXACT COSMIC STRING SOLUTIONS BASED ON THE CONTINUUM THEORY OF DISLOCATIONS

1994 ◽  
Vol 09 (23) ◽  
pp. 4101-4127 ◽  
Author(s):  
TAKEHIKO T. FUJISHIRO ◽  
MITSUO J. HAYASHI ◽  
SHOJI TAKESHITA
Keyword(s):  
Exact Solution ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Unit Length ◽  
Three Dimensional ◽  
Continuum Theory ◽  
Fine Tuning ◽  
Dimensional Model ◽  
Einstein Theory ◽  
Deficit Angle

The effective action from the string compactification is studied on the manifolds with absolute parallelism. The cosmic strings can be described naturally by torsion formalism which has a direct analogy with dislocations in three-dimensional crystalline solids. We have found a stringy solution in a six-dimensional model on M4 × T2 which is compatible with that of Greene et al. and a cylindrically symmetric exact solution is obtained, which are different from the exact cosmic string solutions of the Einstein theory ever proposed. We have also obtained an exact solution in a four-dimensional model on M2 × T2 which can be considered as an example of the compactification on the noncompact manifold and may be expected to describe a space–time structure of our universe. The relation between the mass per unit length and the deficit angle is different from but can be consistent with that of the Einstein theory, since our solution could reproduce its prediction with a condition. We could also obtain the maximum value of the mass per unit length μ ~ 10−6 (~ 1022 g/cm ) by fine-tuning a parameter, which is consistent with recent observations. We have discussed the cosmic strings with the deficit angle larger than 2π.

scholarly journals SPACE-TIME VARIABLE SUPERSTRING VACUA (CALABI-YAU COSMIC YARN)

1994 ◽  
Vol 09 (18) ◽  
pp. 3203-3227 ◽  
Author(s):  
PAUL S. GREEN ◽  
TRISTAN HÜBSCH
Keyword(s):  
Superstring Vacua ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Unit Length ◽  
Finite Energy ◽  
Space Time ◽  
Topological Invariant ◽  
Time Variable ◽  
Internal Space ◽  
Lorentzian Case

In a general superstring vacuum configuration, the “internal” space (sector) varies in space-time. When this variation is nontrivial only in two spacelike dimensions, the vacuum contains static cosmic strings with finite energy per unit length and which is, up to interactions with matter, an easily computed topological invariant. The total space-time is smooth although the “internal” space is singular at the center of each cosmic string. In a similar analysis of the Wick-rotated Euclidean model, these cosmic strings acquire expected self-interactions. Also, a possibility emerges to define a global time in order to rotate back to the Lorentzian case.

Reheating constraints on an inflation model with nonminimal derivative coupling in the light of Planck 2018 data

2020 ◽  
pp. 2150012
Author(s):  
F. S. Mirtalebian ◽  
Kourosh Nozari ◽  
Tahereh Azizi
Keyword(s):  
Equation Of State ◽  
Spectral Index ◽  
Parameter Space ◽  
State Parameter ◽  
Effective Equation ◽  
Derivative Coupling ◽  
Inflation Model ◽  
Scalar Spectral Index ◽  
Equation Of State Parameter ◽  
Inflationary Models

Reheating is a process by which the inflaton’s energy density transfers to conventional matter after cosmic inflation. Currently, there is no cosmic observational evidence to directly detect the reheating era, but it may impose additional constraints on inflationary models. Depending upon the model, e-folding number during reheating [Formula: see text] and the final reheating temperature [Formula: see text], as well as its effective equation of state parameter [Formula: see text], may be directly linked to the inflation observables such as the scalar spectral index [Formula: see text] and the tensor-to-scalar ratio [Formula: see text]. By restricting the values of the effective equation of state parameter observationally, one can derive more stringent limits on inflationary models than those obtained from other routes. In this paper, we are interested to consider the reheating era in an inflation model with a nonminimal derivative coupling of the scalar field to impose some severe constraints on the parameter space of the model in the light of Planck 2018 data. We study the reheating final temperature and e-folds number in terms of the scalar spectral index and [Formula: see text] within a numerical analysis on the model’s parameter space. To realize a viable range of the reheating equation of state parameter in this nonminimal derivative inflation model, we obtain some observationally acceptable subspaces in the [Formula: see text] phase plane. To this end, we consider some sort of polynomial potentials to obtain some constraints on the model’s parameter space which corresponds to viable values of the scalar spectral index and tensor-to-scalar ratio released by Planck 2018 TT+TE+EE+LowE observational data. Finally, we compare the obtained constraints in this nonminimal set-up with those derived from a single, minimally coupled scalar field inflation model to reveal the physics of the reheating in the context of nonminimal derivative inflation model.

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 Searching for gravitational-wave bursts from cosmic string cusps with the Parkes Pulsar Timing Array

2020 ◽  
Vol 501 (1) ◽  
pp. 701-712
Author(s):  
N Yonemaru ◽  
S Kuroyanagi ◽  
G Hobbs ◽  
K Takahashi ◽  
X-J Zhu ◽  
...  
Keyword(s):  
False Alarm ◽  
Gravitational Wave ◽  
Cosmic String ◽  
Cosmic Strings ◽  
False Alarm Probability ◽  
String Tension ◽  
Detection Algorithm ◽  
Pulsar Timing ◽  
Upper Limits ◽  
Pulsar Timing Array

ABSTRACT Cosmic strings are potential gravitational-wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for a GW burst from a cusp on a cosmic string, and apply it to Parkes PTA data. We find four events with a false alarm probability less than 1 per cent. However further investigation shows that all of these are likely to be spurious. As there are no convincing detections we place upper limits on the GW amplitude for different event durations. From these bounds we place limits on the cosmic string tension of Gμ ∼ 10−5, and highlight that this bound is independent from those obtained using other techniques. We discuss the physical implications of our results and the prospect of probing cosmic strings in the era of Square Kilometre Array.

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