IPM Institute for Studies in Theoretical Physics and Mathematics

Tehrān, Iran

IPM Institute for Studies in Theoretical Physics and Mathematics

Tehrān, Iran

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Rahvar S.,Sharif University of Technology | Rahvar S.,IPM Institute for Studies in Theoretical Physics and Mathematics | Mehrabi A.,Sharif University of Technology | Dominik M.,University of St. Andrews
Monthly Notices of the Royal Astronomical Society | Year: 2011

Detecting compact objects such as black holes, white dwarfs, strange (quark) stars and neutron stars by means of their gravitational lensing effect on an observed companion in a binary system has already been suggested almost four decades ago. However, these predictions were made even before the first observations of gravitational lensing, whereas nowadays gravitational microlensing surveys towards the Galactic bulge yield almost 1000 events per year where one star magnifies the light of a more distant one. With a specific view to those experiments, we therefore carry out simulations to assess the prospects for detection of the transient periodic magnification of the companion star, which lasts typically only a few hours in binaries involving a main-sequence star. We find that the effect is practically independent of the distance of the binary system from the observer, but a limit to its detectability is given by the achievability of dense monitoring with the required photometric accuracy. In sharp contrast to earlier expectations by other authors, we find that main-sequence stars are not substantially less favourable targets to observe this effect than white dwarfs, not only because of a better achievable photometry on the much brighter targets, but even more due to the fact that there are≳104≳times as many objects that can be monitored. The requirement of an almost edge-on orbit leads to a probability of the order of≳3 × 10-4≳for spotting the signature of an existing compact object in a binary system with this technique. Assuming an abundance of such systems of about 0.4 per cent, a high-cadence monitoring every 15 min with 5 per cent photometric accuracy would deliver a signal rate per target star of≳γ~ 4 × 10-7 yr-1≳at a recurrence period of about 6 months. With microlensing surveys having demonstrated the capability to monitor about≳2 × 108≳stars, one is therefore provided with the chance to detect roughly semi-annually recurring self-lensing signals from several compact objects in a binary system. These must not be mistaken for similar signatures that arise from isolated planetary mass objects that act as gravitational lens on a background star. If the photometric accuracy was pushed down to 0.3 per cent, 10 times as many signals would become detectable. © 2010 The Authors. Journal compilation © 2010 RAS.


Haghi H.,Institute for Advanced Studies in Basic Sciences | Rahvar S.,IPM Institute for Studies in Theoretical Physics and Mathematics
International Journal of Theoretical Physics | Year: 2010

A simple model for the dynamics of the Magellanic Stream (MS), in the framework of modified gravity models is investigated. We assume that the galaxy is made up of baryonic matter out of context of dark matter scenario. The model we used here is named Modified Gravity (MOG) proposed by Moffat (J. Cosmol. Astropart. Phys. 003, 2005). In order to examine the compatibility of the overall properties of the MS under the MOG theory, the observational radial velocity profile of the MS is compared with the numerical results using the χ2 fit method. In order to obtain the best model parameters, a maximum likelihood analysis is performed. We also compare the results of this model with the Cold Dark Matter (CDM) halo model and the other alternative gravity model that proposed by Bekenstein (Phys. Rev. D 70:083509, 2004), so called TeVeS. We show that by selecting the appropriate values for the free parameters, the MOG theory seems to be plausible to explain the dynamics of the MS as well as the CDM and the TeVeS models. © Springer Science+Business Media, LLC 2010.


Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Atashbar Tehrani S.,IPM Institute for Studies in Theoretical Physics and Mathematics | Olness F.,Southern Methodist University | And 3 more authors.
Nuclear Physics B - Proceedings Supplements | Year: 2010

We investigate the nonsinglet spin-dependent structure function for polarized deep inelastic scattering (DIS) of leptons on nucleons in the next-to-leading-order (NLO) approximation. We perform a fit to extract the polarized parton distribution functions (PPDFs) and the nonsinglet spin structure function using the most recent proton and neutron DIS data. We demonstrate that our results yield good agreement with available observables. © 2010 Elsevier B.V.


Khanpour H.,Semnan University | Khanpour H.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Tehrani S.A.,IPM Institute for Studies in Theoretical Physics and Mathematics
International Journal of Modern Physics A | Year: 2011

In this article we present a determination of the strong coupling constant and parton distribution functions (PDFs) based on a next-to-leading order (NLO) perturbative QCD analysis of proton structure function. More precisely, we extract αs (MZ 2) and PDFs by fitting perturbative QCD predictions to the data from the measurements of the proton structure function F2 p in deep inelastic scattering, which are based on perturbative QCD calculations up to NLO. We obtain at NLO αs(MZ 2) = 0.1154 ± 0.0026 in the variable-flavor number scheme. © 2011 World Scientific Publishing Company.


Arbabifar F.,Semnan University | Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Monfared S.T.,Semnan University | And 2 more authors.
International Journal of Modern Physics A | Year: 2011

We present the results of our QCD analysis for quark distributions and structure functions for polarized deep inelastic scattering of leptons on nucleons and nuclei using the Jacobi polynomials up to NLO approximation. Finally by having proton and also neutron structure functions, we have enough motivation to extract 3He and 3H polarized structure functions. © 2011 World Scientific Publishing Company.


Khanpour H.,Semnan University | Khanpour H.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics
Acta Physica Polonica B | Year: 2010

Utilizing recent deep inelastic scattering data and our recent NLO analysis, we present a QCD analysis of the proton in order to determine the parton distributions at next-to-next-to-leading order (NNLO) of QCD. We also study the heavy quark contributions to the proton structure function F 2 i(x, Q2), with i = c, b. Our NNLO analysis will be performed within the modified minimal subtraction factorization and renormalization scheme. This analysis is undertake within the framework of the so-called "zero-mass variable flavor number scheme" (ZM-VFNS) parton model predictions at high energy colliders where the heavy quarks (c, b, t) considered as massless partons within the nucleon.


Tehrani S.A.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,Semnan University | Monfared S.T.,IPM Institute for Studies in Theoretical Physics and Mathematics | And 2 more authors.
AIP Conference Proceedings | Year: 2011

We present a comprehensive analysis of the structure functions for the polarized nuclei 3He, and focus on the polarized distribution functions and light-cone momentum distributions of protons and neutrons. We demonstrate that the first moment of the 3He structure function can provide an incisive test of the Bjorken sum rule. © 2011 American Institute of Physics.


Khanpour H.,Semnan University | Khanpour H.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Atashbar Tehrani S.,IPM Institute for Studies in Theoretical Physics and Mathematics
Few-Body Systems | Year: 2012

Utilizing very recent deep inelastic scattering measurements, a QCD analysis of proton structure function F p 2(x, Q 2) is presented. A wide range of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data used in order to extract an updated set of parton distribution functions (PDFs). The HERA 'combined' data set on σ ± r,NC(x, Q 2) together with all available published data for heavy quarks F c,b 2(x, Q 2), longitudinal F L (x, Q 2) and also very recent reduced DIS cross section σ ± r,NC(x, Q 2) data from HERA experiments are the input in the present next-to-leading order (NLO) QCD analysis which determines a new set of parton distributions, called KKT11C. The extracted PDFs in the 'fixed flavour number scheme' (FFNS) are in very good agreement with the available theoretical models. © 2011 Springer-Verlag.


Arbabifar F.,Semnan University | Arbabifar F.,IPM Institute for Studies in Theoretical Physics and Mathematics | Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | And 3 more authors.
Nuclear Physics B - Proceedings Supplements | Year: 2013

We perform a new extraction for unpolarized and polarized parton distribution functions considering a flavor decompositions for sea quarks and applying very recent deep inelastic scattering (DIS) and semi inclusive deep inelastic scattering (SIDIS) data in the fixed flavor number scheme (FFNS) framework. In the new symmetry breaking scenario the light quark and antiquark densities are extracted separately and new parametrization forms are determined for them. The heavy flavors contribution, including charm and bottom quarks, are also taken to be account for unpolarized distributions. © 2012 Elsevier B.V.


Khorramian A.N.,Semnan University | Khorramian A.N.,IPM Institute for Studies in Theoretical Physics and Mathematics | Atashbar Tehrani S.,Semnan University | Atashbar Tehrani S.,IPM Institute for Studies in Theoretical Physics and Mathematics
Applied Mathematics and Information Sciences | Year: 2010

We study the heavy-quark contribution to the longitudinal proton structure function FL(x;Q2). In our QCD calculations we extract light and asymptotic heavy flavor contributions for the non-singlet, singlet and gluon parts due to charm to FL. Our calculations for longitudinal proton structure function based on the Jacobi polynomials method are in good agreement with very recent H1 experimental data. © 2009 Dixie W Publishing Corporation, U.S.A.

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