scholarly journals Barotropic FRW cosmologies with Chiellini damping in comoving time

2015 ◽  
Vol 30 (20) ◽  
pp. 1550100 ◽  
Author(s):  
Haret C. Rosu ◽  
Stefan C. Mancas ◽  
Pisin Chen
Keyword(s):  
Cosmological Constant ◽  
Conformal Time ◽  
Identical Form ◽  
Scale Factors ◽  
Hypergeometric Solutions ◽  
Time Lead ◽  
Dissipative Scale

For nonzero cosmological constant Λ, we show that the barotropic FRW cosmologies as worked out in the comoving time lead in the radiation-dominated case to scale factors of identical form as for the Chiellini dissipative scale factors in conformal time obtained recently by us in Phys. Lett. A 379, 882 (2015). This is due to the Ermakov equation which is obtained in this case. For zero cosmological constant, several textbook solutions are easily obtained as particular cases of our formulas and hypergeometric solutions are also reminded.

scholarly journals DARBOUX CLASS OF COSMOLOGICAL FLUIDS WITH TIME-DEPENDENT ADIABATIC INDICES

2000 ◽  
Vol 15 (15) ◽  
pp. 979-990 ◽  
Author(s):  
H. C. ROSU
Keyword(s):  
Mathematical Method ◽  
Cosmological Constant ◽  
Time Dependence ◽  
Adiabatic Index ◽  
Time Dependent ◽  
Accelerating Universe ◽  
Constant Parameter ◽  
Darboux Transformations ◽  
Scale Factors ◽  
Experimental Findings

A one-parameter family of time-dependent adiabatic indices is introduced for any given type of cosmological fluid of constant adiabatic index by a mathematical method belonging to the class of Darboux transformations. The procedure works for zero cosmological constant at the price of introducing a new constant parameter related to the time dependence of the adiabatic index. These fluids can be the real cosmological fluids that are encountered at cosmological scales and they could be used as a simple and efficient explanation for the recent experimental findings regarding the present day accelerating universe. In addition, new types of cosmological scale factors, corresponding to these fluids, are presented.

scholarly journals COSMOLOGICAL CONSTANT OF THE INFLATING BRANES IN THE RANDALL–SUNDRUM–ODA MODEL

2001 ◽  
Vol 16 (30) ◽  
pp. 1933-1940 ◽  
Author(s):  
LAURA MERSINI
Keyword(s):  
Cosmological Constant ◽  
Source Term ◽  
Einstein Equations ◽  
Expansion Rate ◽  
Fifth Dimension ◽  
Scale Factors ◽  
Slow Roll ◽  
Effective Expansion ◽  
The Many ◽  
Decreasing Functions

We examine the issue of the cosmological constant in the many inflating branes scenario, extending on two recent models by I. Oda and Randall–Sundrum. The exact solution in a closed form is found in the slow-roll approximation for the branes. We show that each positive tension brane has an induced canonical cosmological constant and expansion rate that are decreasing functions of their position in the fifth dimension. The reason is that the square of the effective expansion rate enters as a source term in the Einstein equations for the branes. Thus the brane has two scale factors depending on time and the fifth dimension respectively. A displacement of the brane along the fifth dimension would adjust its effective expansion rate in such a way that it compensates for its internal energy changes due to inflation and possible phase transitions.

Classical and quantum cosmological solutions in Bianchi type-I metric with fermionic field and relativistic fluid in Schutz’s formalism

2019 ◽  
Vol 34 (33) ◽  
pp. 1950271 ◽  
Author(s):  
Marlos O. Ribas ◽  
Fernando P. Devecchi ◽  
Gilberto M. Kremer
Keyword(s):  
Degrees Of Freedom ◽  
Bianchi Type ◽  
Hamiltonian Formalism ◽  
Inflationary Universe ◽  
Type I ◽  
Conformal Time ◽  
Fermionic Field ◽  
Bianchi Type I ◽  
Relativistic Fluid ◽  
Scale Factors

A model for an anisotropic pre-inflationary universe described by the Bianchi type-I metric is developed. A relativistic fluid of the Schutz formalism and a self-interacting fermionic field are considered as sources of the gravitational field. The classical analysis is based on the Hamiltonian formalism written in terms of the Misner variables and it is shown that the fluid degrees of freedom can be embodied by a conformal time variable. The three classical scale factors are obtained as functions of the conformal time. The quantum analysis follows from the de Broglie–Bohm formalism applied to the wave function which is a solution of the Wheeler–DeWitt equation and the three scale factors are also determined as functions of the conformal time. While the classical expressions for the scale factors show a singularity when the conformal time vanishes, their quantum expressions exhibit bouncing behavior. It is possible to adjust the behavior of the classical and quantum scale factors as functions of the conformal time so that they have a common isotropic behavior at late times with a dilution of the quantum effects.

PERUBAHAN NILAI BUDAYA MINANGKABAU DALAM NOVEL TENGGELAMNYA KAPAL VAN DER WIJCK KARYA HAMKA DAN NOVEL BULAN SUSUT KARYA ISMET FANANY (KAJIAN PERBANDINGAN)

Jurnal KATA ◽  
2018 ◽  
Vol 2 (2) ◽  
pp. 336
Author(s):  
Yulia Pebriani
Keyword(s):  
Modern Society ◽  
Local Culture ◽  
The Novel ◽  
Next Generation ◽  
The Status ◽  
Symbolic Leadership ◽  
Cultural Shifts ◽  
Time Lead

<em>Local culture is very diverse Indonesia became an honor and challenge to maintain and inherited to the next generation. Local Indonesian culture is very proud because it has a very varied diversity and unique. As time, lead to changes in lifestyle a more modern society. As a result, people will prefer the new culture that may be considered more practical than the local culture. Views on kinship, treasures, and wander in the novel Tenggelamnya Kapal Van Der Wijck Hamka works and novels Bulan Susut works Ismet Fanany changes and cultural shifts. Kinship, treasures, and wander in the novel Sinking Ship Van Der Wijck Hamka's work is described explicitly, whereas kinship, treasures, and wander in the novel Month Losses Ismet work Fanany described implicitly. Changes in people's lives has implications for social Minangkabau culture in Minangkabau society. A leadership that is both functional mamak transformed into symbolic leadership. Mamak originally as straps tribesmen, has changed the status and intrinsic meaning.</em>

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

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