Superalgebra and Harmonic Oscillator with Constant Positive Curvature
This paper has been withdrawn by the author due to a error in attachment of source file.
math-ph↗
arXiv subjects
J. Sadeghi
Publications and source records attributed to J. Sadeghi.
Stability analysis of agegraphic dark energy in Brans-Dicke cosmology
Stability analysis of agegraphic dark energy in Brans-Dicke theory is presented in this paper. We constrain the model parameters with the observational data and thus the results become broadly consistent with those expected from experiment. Stability analysis of the model without best fitting shows that universe may begin from an unstable state passing a saddle point and finally become stable in future. However, with the best fitted model, There is no saddle intermediate state. The agegraphic dark energy in the model by itself exhibits a phantom behavior. However, contribution of cold dark matter on the effective energy density modifies the state of teh universe from phantom phase to quintessence one. The statefinder diagnosis also indicates that the universe leaves an unstable state in the past, passes the LCDM state and finally approaches the sable state in future.
physics.gen-ph↗
Logarithmic entropy--corrected holographic dark energy with non--minimal kinetic coupling
In this paper, we have considered a cosmological model with the non--minimal kinetic coupling terms and investigated its cosmological implications with respect to the logarithmic entropy-- corrected holographic dark energy (LECHDE). The correspondence between LECHDE in flat FRW cosmology and the phantom dark energy model with the aim to interpret the current universe acceleration is also examined.
hep-th↗
The effect of higher derivative correction on $η/s$ and conductivities in STU model
In this paper we study the ratio of shear viscosity to entropy, electrical and thermal conductivities for the R-charged black hole in STU model. We generalize previous works to the case of a black hole with three different charges. Actually we use diffusion constant to obtain ratio of shear viscosity to entropy. By applying the thermodynamical stability we recover previous results. Also we investigate the effect of higher derivative corrections.
hep-th↗
Particle acceleration in Horava-Lifshitz black holes
In this paper we calculate the center-of-mass energy of two colliding test particles near the rotating and non-rotating Horava-Lifshitz black hole. For the case of slowly rotating KS solution of Horava-Lifshitz black hole we compare our results with the case of Kerr black holes. We confirm the limited value of the center-of-mass energy for the static black holes and unlimited value of the center-of-mass energy for the rotating black holes. Numerically, we discuss temperature dependence of the center-of-mass energy on the black hole horizon. We obtain the critical angular momentum of particles. In this limit the center-of-mass energy of two colliding particles in the neighborhood of the rotating Horava-Lifshitz black hole could be arbitrarily high. We found appropriate conditions where the critical angular momentum could have an orbit outside the horizon. Finally, we obtain center-of-mass energy corresponding to this circle orbit.
hep-th↗
Cosmic String in the BTZ Black Hole Background with Time-Dependant Tension
In this paper, we study the equation of circular loops with time-dependant tension in the BTZ black hole background. We obtain various cases where cosmic string loops finally collapse to form black holes. Also, we study effect of the BTZ black hole mass and angular momentum on the evolution of cosmic string loops. We find the critical values of initial radii as a limit for the cosmic string loops collapsing to form black holes.
hep-th↗
Thermodynamical Stability of Hagedorn and Radiation Regimes in Closed String Gas Cosmology
In this paper, we investigate thermal equilibrium in string gas cosmology which is dominated by closed string.We consider two interesting regimes, Hagedorn and radiation regimes.We find that for short strings in small radius of Hagedorn regime very large amount of energy requested to have thermal equilibrium but for long strings in such system a few energy is sufficient to have thermal equilibrium. On the other hand in the large radius of Hagedorn regime, which pressure is not negligible, we obtain a relation between the energy and pressure in terms of cosmic time which is satisfied by thermal equilibrium. Then we discuss about radiation regime and find that in all cases there is thermal equilibrium.
hep-th↗
The Holographic Description of Baryon in Non- Critical String Theory
We consider a holographic model constructed from an intersecting brane configuration $D4/D4/\bar{D4}$ in noncritical string theory. We study the baryon in the confined phase of this supergravity by considering the source term for the baryon. Also, the thermodynamics functions are studied. Moreover, we obtain the binding energy of the baryon in this holographic QCD-like model.
hep-th↗
Decay widths of large-spin mesons from the non-critical string/gauge duality
In this paper, we use the non-critical string/gauge duality to calculate the decay widths of large-spin mesons. Since it is believed that the string theory of QCD is not a ten dimensional theory, we expect that the non-critical versions of ten dimensional black hole backgrounds lead to better results than the critical ones. For this purpose we concentrate on the confining theories and consider two different six dimensional black hole backgrounds. We choose the near extremal AdS6 model and the near extremal KM model to compute the decay widths of large-spin mesons. Then, we present our results from these two non-critical backgrounds and compare them together with those from the critical models and experimental data.
hep-th↗
Calculating the jet-quenching parameter in STU background
In this paper we use the AdS/CFT correspondence to compute the jet-quenching parameter in a N=2 thermal plasma. We consider the general three-charge black hole and discuss some special cases. We add a constant electric field to the background and find the effect of the electric field on the jet-quenching parameter. Also we include higher derivative terms and obtain the first-order correction for the jet-quenching parameter.
hep-th↗
Bouncing Universe and Reconstructing Vector Field
Motivated by the recent works of Refs. \cite{R1, R2} where a model of inflation has been suggested with non-minimally coupled massive vector fields, we generalize their work to the study of the bouncing solution. So we consider a massive vector field, which is non-minimally coupled to gravity. Also we consider non-minimal coupling of vector field to the scalar curvature. Then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy. Finally we simply plot reconstructed physical quantities in flat universe.
hep-th↗
Jet-quenching of the rotating heavy meson in a ${\mathcal{N}}$=4 SYM plasma in presence of a constant electric field
In this paper, we consider a rotating heavy quark-antiquark ($q\bar{q}$) pair in a ${\mathcal{N}}$=4 SYM thermal plasma. We assume that $q\bar{q}$ center of mass moves at the speed $v$ and furthermore they rotate around the center of mass. We use the AdS/CFT correspondence and consider the effect of external electromagnetic field on the motion of the rotating meson. Then we calculate the jet-quenching parameter corresponding to the rotating meson in the constant electric field.
hep-th↗
Screening Length of Rotating Heavy Meson from AdS/CFT
In this paper we consider a quark-antiquark ($q\bar{q}$) pair which can be interpreted as a meson in ${\mathcal{N}}$=4 SYM thermal plasma. We assume that the string moves at speed $v$ and rotates around its center of mass simultaneously. By using the AdS/CFT correspondence, we obtain the momentum densities of the rotating string and determine its motion for small angular velocities. Then in general case, we calculate the screening length of $q\bar{q}$ pair numerically and show that its velocity dependance is in consistent with the well known formula $L_s T\sim (1-v^{2})^{1/4}$ in the literature.
hep-th↗
Baryon Binding Energy in Sakai-Sugimoto Model
The binding energy of baryon has been studied in the dual $AdS_5\times S^5$ string theory with a black hole interior. In this picture baryon is constructed of a $D_5$ brane vertex wrapping on $S^5$ and $N_c$ fundamental strings connected to it. Here, we calculate the baryon binding energy in Sakai-Sugimoto model with a $D_4/D_8/\bar{D_8}$ in which the supersymmetry is completely broken. Also we check the $T$ dependence of the baryon binding energy. We believe that this model represents an accurate description of baryons due to the existence of Chern-Simones coupling with the gauge field on the brane. We obtain an analytical expression for the baryon binding energy . In that case we plot the baryon binding energy in terms of radial coordinate. Then by using the binding energy diagram, we determine the stability range for baryon configuration. And also the position and energy of the stable equilibrium point is obtained by the corresponding diagram. Also we plot the baryon binding energy in terms of temperature and estimate a critical temperature in which the baryon would be dissociated.
hep-th↗
Drag force with different charges in STU background and $AdS$/CFT
In this paper we consider the drag force problem in the STU model. Already this problem and related topics were studied in ${\mathcal N}=4$ SYM theory. Here we study the same problem in ${\mathcal N}=2$ supergravity theory with an R-charge black hole (the STU model). This paper extends our previous work [1,2] by studying more general charge configurations and by taking into account the effect of a constant electromagnetic field and higher derivative corrections. We consider a single quark and a $q \bar q$ pair in a three charge non-extremal black hole background. First by using the AdS/CFT correspondence, we obtain the drag force, the diffusion coefficient, the total energy and momentum, quasinormal modes, and the effect of higher derivative corrections for the single quark. Next we calculate the drag force for a $q \bar q$ pair which rotates around its center of mass. For the first time we study the motion of a rotating $q \bar q$ pair in ${\mathcal N}=2$ supergravity theory. We show that our results in the near-extremal limit agree with the energy loss of the moving quark which was calculated in the ${\mathcal N}=4$ SYM plasma.
hep-th↗
Bouncing universe with the non-minimally coupled scaler field and its reconstructing
In this paper we consider a non-minimally coupled scaler field, and show its equation of state parameter can crossing over -1, $ω\to -1$, and bouncing condition. Also we obtain the stability conditions and consider reconstructing for our model.
gr-qc↗
The orbit method solution for the deformed three coupled scalar fields
In this work, we present a deformed solutions starting from systems of three coupled scalar fields with super-potential $W(ϕ_1, ϕ_2, ϕ_3)$ by orbit method. First, we deform the corresponding super-potential and obtain defect solutions. It is shown that how to construct new models altogether with its defect solutions in terms of the non-deformed model. Therefore, we draw the graph of super-potential and different fields in terms of $x.$ So we observe that the graphs for deformed and non - deformed cases are changed by the scale.
math-ph↗
Time-dependent backgrounds of two dimensional string theory from the $c=1$ matrix model
The aim of this paper is to use correspondence between solutions in the $c=1$ matrix model collective field theory and coupled dilaton-gravity to a massless scalar field. First, we obtain the incoming and outgoing fluctuations for the time-dependent backgrounds with the lightlike and spacelike boundaries. In the case of spacelike boundaries, we have done here for the first time. Then by using the leg-pole transformations we find corresponding tachyon field in two dimensional string theory for lightlikes and spacelikes boundary.
hep-th↗