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S. Rouhani

Publications and source records attributed to S. Rouhani.

At least 55 records · Page 3Linked to original sources
arXiv2005

A Computational Fluid Model for Investigation of Plasma Waves and Instabilities

A computational fluid model is developed to study waves and instabilities. A new technique involving initial perturbations in configuration space have been implemented to excite the plasma waves; i.e. the perturbations acting similar to a random velocity distribution in particle in cell (PIC) codes. This forms a new powerful tool for investigation of many waves arising in both thermal and cold plasmas and as such will allow investigation of problems demanding scales and resolution not yet possible by PIC codes. The model predicts Langmuir waves, two stream instabilities, nonlinear wave-wave interaction, and the Debye screening effects. The agreement between theory and simulation where analytic results are available are excellent.

physics.plasm-ph↗
arXiv2004

On the Probability of Occurrence of Clusters in Abelian Sandpile Model

We have performed extensive simulations on the Abelian Sandpile Model (ASM) on square lattice. We have estimated the probability of observation of many clusters. Some are in good agreement with previous analytical results, while some show discrepancies between simulation and analytical results.

cond-mat.stat-mech↗
arXiv2004

Tree-level Scattering Amplitude in de Sitter Space

In previous papers [1,2], it was proved that a covariant quantization of the minimally coupled scalar field in de Sitter space is achieved through addition of the negative norm states. This causal approach which eliminates the infrared divergence, was generalized further to the calculation of the graviton propagator in de Sitter space [3] and one-loop effective action for scalar field in a general curved space-time [4]. This method gives a natural renormalization of the above problems. Pursuing this approach, in the present paper the tree-level scattering amplitudes of the scalar field, with one graviton exchange, has been calculated in de Sitter space. It is shown that the infrared divergence disappears and the theory automatically reaches a renormalized solution of the problem.

gr-qc↗
arXiv2004

Logarithmic Conformal Null Vectors and SLE

Formal Loewner evolution is connected to conformal field theory. In this letter we introduce an extension of Loewner evolution, which consists of two coupled equations and connect the martingales of these equations to the null vectors of logarithmic conformal field theory.

hep-th↗
arXiv2004

Correlation Functions and AdS/LCFT Correspondence

Correlation functions of Logarithmic conformal field theory is investigated using the ADS/CFT correspondence and a novel method based on nilpotent weights and 'super fields'. Adding an specific form of interaction, we introduce a perturbative method to calculate the correlation functions.

hep-th↗
arXiv2004

Exact analytical expression for magnetoresistance using quantum groups

We obtain an exact analytical expression for magnetoresistance using noncommutative geometry and quantum groups.Then we will show that there is a deep relationship between magnetoresistance and the quantum group $su_{q}(2)$, from which we understand the quantum interpretation of the quantum corrections to the conductivity.

cond-mat.dis-nn↗
arXiv2002

Use of Nilpotent weights in Logarithmic Conformal Field Theories

We show that logarithmic conformal field theories may be derived using nilpotent scale transformation. Using such nilpotent weights we derive properties of LCFT's, such as two and three point correlation functions solely from symmetry arguments. Singular vectors and the Kac determinant may also be obtained using these nilpotent variables, hence the structure of the four point functions can also be derived. This leads to non homogeneous hypergeometric functions. Also we consider LCFT's near a boundary. Constructing "superfields" using a nilpotent variable, we show that the superfield of conformal weight zero, composed of the identity and the pseudo identity is related to a superfield of conformal dimension two, which comprises of energy momentum tensor and its logarithmic partner. This device also allows us to derive the operator product expansion for logarithmic operators. Finally we discuss the AdS/LCFT correspondence and derive some correlation functions and a BRST symmetry.

hep-th↗
arXiv2001

On the AdS/CFT Correspondence and Logarithmic Operator

Logarithmic conformal field theory is investigated using the AdS/CFT correspondence and a novel method based on nilpotent weights. Using this device we add ghost fermions and point to a BRST invariance of the theory.

hep-th↗
arXiv2001

Fractal Behavior of Flow of an Inhomogeneous Fluid Over a Smooth Inclined Surface

Patterns formed by the flow of an inhomogeneous fluid (suspension) over a smooth inclined surface were studied. It was observed that for inclination angle larger than a threshold, global fractal patterns are formed. The fractal dimensions of these patterns were measured df=1.35-1.45 which corresponds to that observed for the flow of water over an inhomogeneous surface, implying that this system is within the same universality class. Except that here the disorder is present in the fluid and is transferred to the surface. This observation is in agreement with the result of the theories of nonlinear flow of fluid in disordered media.

cond-mat.dis-nn↗
arXiv2001

Exact Enumeration of Two-Dimensional Closed Random Paths Using a DSP Processor

The aim of this paper is to show that Digital Signal Processors (DSPs) can be used to efficiently implement complex algorithms. As an example we have chosen the problem of enumerating closed two-dimensional random paths. An Evaluation Module Board (EVM) for TMS320C6201 fixed-point processor is used. The algorithm is implemented in hand-written parallel assembly language. Some techniques are used to fit the algorithm to the parallel structure of the processor and also to avoid Branch and Condition-Checking tasks. Common optimization methods are also employed to improve the execution speed of the code. These methods are shown to yield a good efficiency in using the maximum computation power of the processor. We use these results to obtain the area distribution of the paths.

physics.comp-ph↗
arXiv2000

Logarithmic Conformal Field Theory Through Nilpotent Conformal Dimensions

We study logarithmic conformal field theories (LCFTs) through the introduction of nilpotent conformal weights. Using this device, we derive the properties of LCFT's such as the transformation laws, singular vectors and the structure of correlation functions. We discuss the emergence of an extra energy momentum tensor, which is the logarithmic partner of the energy momentum tensor.

hep-th↗
arXiv2000

Current Algebra Associated with Logarithmic Conformal Field Theories

We propose a general frame work for deriving the OPEs within a logarithmic conformal field theory (LCFT). This naturally leads to the emergence of a logarithmic partner of the energy momentum tensor within an LCFT, and implies that the current algebra associated with an LCFT is expanded. We derive this algebra for a generic LCFT and discuss some of its implications. We observe that two constants arise in the OPE of the energy-momentum tensor with itself. One of these is the usual central charge.

hep-th↗
arXiv2000

Logarithmic Conformal Field Theories Near a Boundary

We consider logarithmic conformal field theories near a boundary and derive the general form of one and two point functions. We obtain results for arbitrary and two dimensions. Application to two dimensional magnetohydrodynamics is discussed.

hep-th↗
arXiv1998

Zamalodchikov's C-Theorem and The Logarithmic Conformal Field Theory

We consider perturbation of a conformal field theory by a pair of relevant logarithmic operators and calculate the beta function up to two loops. We observe that the beta function can not be derived from a potential. Thus the renormalization group trajectories are not always along decreasing values of the central charge. However there exists a domain of structure constants in which the c-theorem still holds.

hep-th↗