arXiv subjects

Mahmud Bahmanabadi

Publications and source records attributed to Mahmud Bahmanabadi.

4 recordsLinked to original sources

arXiv2018

Revisiting nonrelativistic limits of field theory: Antiparticles

Different subtleties and problems associated with a nonrelativistic limit of the field theory to the Schroedinger theory are discussed. In this paper, we revisit different cases of the nonrelativistic limit of a real and complex scalar field in the level of the Lagrangian and the equation of motion. We develop the nonrelativistic limit of the Dirac equation and action in the way that the nonrelativistic limit of spin-$\frac{1}{2}$ wave functions of particles and antiparticles appear simultaneously. We study the effect of a potential like $U(ϕ)\propto ϕ^4$ which can be attributed to axion dark matter field in this limit. We develop a formalism for studying the nonrelativistic limit of antiparticles in the quantum mechanics. We discussed the non-local approach for the nonrelativistic limit and its problems.

hep-th↗

arXiv2017

Distinguishing Thermal Fluctuations from Instrumental Error for High Pressure Charged Gas

Thermodynamic parameters such as temperature and pressure can be defined from the statistical behavior of a system. Therefore, thermal fluctuation is an inseparable characteristic of these parameters which eventually finds its way into experimental data. Analyzing these fluctuations is very useful in studying the phase transitions of a physical system or its behavior around critical points. However, this approach is not straightforward as most of the times it is impossible to distinguish meaningful thermal fluctuations from those due to the instrumental errors. In this article, we have offered a method by which an experimenter can separate this multi-sourced fluctuation into its constitutive parts according to their sources. Although the article is only focused on a specific system, which is a high pressure charged gas, we have used a computational method which could be used for various other systems. Our proposed idea is very efficient and reduces the required computation time by a remarkable fraction. We have used Euler algorithm, which generally does not hold the internal energy conserved; But we have used this fact as a tool which allows us to surf in the phase space of the system and reach different energy levels in significantly less time. Although system does not spend enough time in a single energy level to equilibrate, but we have been able to extract the details of the equilibrium state out of our data. Using numerical computations combined with theoretical modelings we have given a final expression for the amount of the overall fluctuations existing in the measured pressure values. This expression is given in terms of the characteristics of both the gas and the barometer so that it can be experimentally verified.

physics.comp-ph↗

arXiv2014

Alborz-I array: a simulation on performance and properties of the array around the knee of the cosmic ray spectrum

The first phase of the Alborz Observatory Array (Alborz-I) consists of 20 plastic scintillation detectors each one with surface area of 0.25 $m^{2}$ spread over an area of 40$\times$40 $m^{2}$ realized to the study of Extensive Air Showers around the $\it knee$ at the Sharif University of Technology campus. The first stage of the project including construction and operation of a prototype system has now been completed and the electronics that will be used in the array instrument has been tested under field conditions. In order to achieve a realistic estimate of the array performance, a large number of simulated CORSIKA~\cite{a} showers have been used. In the present work, theoretical results obtained in the study of different array layouts and trigger conditions are described. Using Monte Carlo simulations of showers the rate of detected events per day and the trigger probability functions, i.e., the probability for an extensive air shower to trigger a ground based array as a function of the shower core distance to the center of array are presented for energies above 1 TeV and zenith angles up to 60$^{\circ}$. Moreover, the angular resolution of the Alborz-I array is obtained.

astro-ph.IM↗

arXiv2014

Scintillation detectors of Alborz-I experiment

A new air shower experiment of the Alborz Observatory, Alborz-I, located at the Sharif University of Technology, Iran, will be constructed in near future. An area of about 30$\times$40 m$^{2}$ will be covered by 20 plastic scintillation detectors (each with an area of 50$\times$50 cm$^{2}$). A series of experiments have been performed to optimize the height of light enclosures of the detectors for this array and the results have been compared to an extended code simulation of these detectors. Operational parameters of the detector obtained by this code are cross checked by Geant4 simulation. There is a good agreement between extended-code and Geant4 simulations. We also present further discussions on the detector characteristics, which can be applicable for all scintillation detectors with a similar configuration.

physics.ins-det↗