Search

We consider the electromagnetic form factors ratio in the Rosenbluth and polarization methods. We explore the impact of adding new particles as the mediators in the electron-proton scattering on these ratios. Consequently, we find some bound on the scalar coupling as $\alpha_{sc}\sim 10^{-5}$ for $m_{sc}\sim 5 MeV-2 GeV$ and $\alpha_{sc}\sim 10^{-4}-10^{-3}$ for $m_{sc}\sim 2-10 GeV$. Meanwhile, the vector coupling is bounded as $\alpha_v\sim 10^{-5}$ for $m_v\sim 5 MeV-1.1 GeV$ and $\alpha_v\sim 10^{-4}-10^{-3}$ for $m_v\sim 1.2-10 GeV$. These constraints are in complete agreement with those which is found from other independent experiments., Comment: 21 pages, 6 figures

We consider a vector dark matter (VDM) with a direct coupling with photon. We examine the effect of such an interaction on the CMB polarization to put new constrains on the properties of the DM particles. We show that a partially polarized VDM of the order of temperature fluctuation with a quadrupole distribution leads to a valuable CP for the CMB. In different DM-models the DM-masses range from few $eV$ to a few $TeV$. We show that the CP angular power spectrum depends on the mass of VDM as $C^{(S)}_{Vl}\propto 1/m_{_{V}}^6$ such that for $m_{_{V}}=10eV-1keV$, the CP angular power spectrum is $C^{(S)}_{Vl}\simeq 10^3- 10^{-11}{\rm nK^2}$. Therefore, the light VDM with masses less than $10 eV$ leads to an unexpected very large CP which can be excluded from the acceptable range of the VDM masses., Comment: 40 pages, 7 figures, Accepted for publication in Physical Review D

In this paper, we explore the possibility of the polarization conversion of a wide energy range of cosmic photons to the circular polarization through their interactions with right handed Sterile neutrinos as a candidate for dark matter. By considering the Sterile neutrino in the seesaw mechanism framework and right-handed current model, we examine the Faraday conversion $\Delta \phi_\text{\tiny{FC}}$ of gamma ray burst (GRB) photons at both the prompt and afterglow emission levels as well as the radio photons emitted from our galaxy and extra-galactic sources interacting with the Sterile neutrinos. Consequently, for the Sterile neutrino with mixing angle $\theta^2\lesssim 10^{-2}$ motivated by models with a hidden sector coupled to the sterile neutrino, the Faraday conversion can be estimated as $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-3}-10^{-18}$ rad for GRB, $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-6}-10^{-11}$ rad for radio emission source from our galaxy and $\Delta \phi_\text{\tiny{FC}}\lesssim 10^{-6}-10^{-15}$ rad for extra-galactic sources. We also examine the V-mode power spectrum $C_{Vl}$ of the cosmic microwave background (CMB) at the last scattering surface. We show that the circular polarization power spectrum at the leading order is proportional to the linear polarization power spectrum $C_{pl}$ and the mixing angle where for $\theta^2\lesssim 10^{-2}$ leads to $C_{Vl}\lesssim 0.01$ Nano-Kelvin squared., Comment: 25 pages, 4 figures and 2 tables

We consider dark matter as singlet fermionic particles which carrying magnetic dipole moment to explore its contribution on the polarization of cosmic microwave background (CMB) photons. We show that Dirac fermionic dark matter has no contribution on the CMB polarization. However, in the case of Majorana dark matter this type of interaction leads to the B-mode polarization in presence of primordial scalar perturbations which is in contrast with standard scenario for the CMB polarization. We numerically calculate the B-mode power spectra and plot $C_l^{BB}$ for different dark matter masses and the $r$-parameter. We show that the dark matter with masses less than 100MeV have valuable contribution on $C_l^{BB}$. Meanwhile, the dark matters with mass $m_d\leq50MeV$ for $r=0.07$ ( $m_d\leq80MeV$ for $r=0.09$) can be excluded experimentally. Furthermore, our results put a bound on the magnetic dipole moment about $M\leq 10^{-16} e\,\,cm$ in agreement with the other reported constraints.

We consider the standard model extension to explore the anomalous magnetic dipole moment of the muon. In the QED part of the theory for the CP and CPT-even Lorentz parameter $c_{\mu\nu}$, all independent electromagnetic form factors depend on a new scalar as $p'.c.p$. Therefore, the form factors, even in zero momentum transfer, can be energy dependent. We examine the magnetic form factor to find such an energy dependent up to the one loop level at the leading order of $c_{\mu\nu}$. We show that at the high energy limit (but low enough to satisfy $p^2/m^2\ll1$) there is an enhancement on the muon anomalous magnetic moment. For the first time, we find a bound on the $c_{\mu\nu}$ components for the muon as $[c_{TT}+0.35(c_{XX}+c_{YY})+0.28c_{ZZ}]$, which is about $10^{-11}$ in a terrestrial experiment, Comment: 21 pages, 1 figure,1 table, and to appear in PRD

We consider the noncommutative Standard Model that contains Lorentz symmetry violation as a subset of the Standard Model extension. We introduce a constant electromagnetic field as a background to derive mutual relations between the free parameters of both theories. As the Lorentz violation parameters of the Standard Model extension are extensively explored in different experiments and many stringent bounds on these parameters are available, we can find new bounds on the scale of noncommutativity of the order of a few to tens of teraelectron volts., Comment: 32 pages, to appear in PRD

It is known that the linearly polarized photons can partly transform to circularly polarized ones via forward Compton scattering in a background such as the external magnetic field or noncommutative space time. Based on this fact we explore the effects of the NC-background on the scattering of a linearly polarized laser beam from an intense beam of charged leptons. We show that for a muon/electron beam flux $\bar\varepsilon_{\mu,e}\sim 10^{12}/10^{10}\,{\rm TeV}\,{\rm cm}^{-2}\,{\rm sec}^{-1}$ and a linearly polarized laser beam with energy $k^0\sim $1 eV and average power $\bar{P}_{\rm laser}\simeq$1 MW, the generation rate of circularly polarized photons is about $R_{_V} \sim 10^4/{\rm sec}$ for Noncommutative energy scale $\Lambda_{\tiny{NC}}\sim 10$TeV. This is fairly large and can grow for more intense beams in near future.

In the standard model of cosmology (SMC) the B-mode polarization of the CMB can be explained by the gravitational effects in the inflation epoch. However, this is not the only way to explain the B-mode polarization for the CMB. It can be shown that the Compton scattering in presence of a background besides generating a circularly polarized microwave, can leads to a B-mode polarization for the CMB. Here we consider the non-commutative (NC) space time as a background to explore the CMB polarization at the last scattering surface. We obtain the B-mode spectrum of the CMB radiation by scalar perturbation of metric via a correction on the Compton scattering in NC-space-time in terms of the circular polarization power spectrum and the non-commutative energy scale. It can be shown that even for the NC-scale as large as $10TeV$ the NC-effects on the CMB polarization and the r-parameter is significant. We show that the V-mode power spectrum can be obtained in terms of linearly polarized power spectrum in the range Micro to Nano-Kelvin squared for the NC-scale about $1TeV$ to $10TeV$, respectively., Comment: 15 pages

We consider the Higgs and Yukawa parts of the Non-Commutative Standard Model (NCSM). We explore the NC-action to give all Feynman rules for couplings of the Higgs boson to electro-weak gauge fields and fermions., Comment: 26 pages

Comparing electronic Hydrogen with muonic Hydrogen shows that the discrepancy in measurement of the Lamb shift in the both systems are relatively of order of $(\frac{m_\mu}{m_e})^{4-5}$. We explore the spectrum of Hydrogen atom in noncommutative $QED$ to compare the noncommutative effects on the both bound states. We show that in the Lorentz violating noncommutative QED the ratio of NC-corrections is $(\frac{m_\mu}{m_e})^3$ while in the Lorentz conserving NCQED is $(\frac{m_\mu}{m_e})^5$. An uncertainty about $1 \,Hz\ll 3\,kHz$ in the Lamb shift of Hydrogen atom leads to an NC correction about $10 \,MHz$ in the Lorentz violating noncommutative QED and about $400 \,GHz$ in the Lorentz conserving noncommutative QED., Comment: 15 pages, to appear in EPJC

We consider the Lorentz violated extension of the standard model. In this framework, there are terms that explicitly violate CP-symmetry. We examine the CPT-even $d_{\mu\nu}$-term to find the electric dipole moment of charged leptons. We show that the form factors besides the momentum transfer, depend on a new Lorentz-scalar, constructing by $d_{\mu\nu}$ and the four momenta of the lepton, as well. Such an energy dependence of the electric dipole form factor leads to an enhancement of the lepton electric dipole moment at high energy, even at the zero momentum transfer. We show that at $\frac{|d|p^2}{m^2_l}\sim 1$ the electric dipole moment of the charged lepton can be as large as $10^{-14} e\,\,cm$., Comment: 15 pages, 1 figure

The noncommutative standard model apparently violates the Lorentz symmetry. We compare the Lorentz violating terms in the Higgs sector of the noncommutative standard model with their counterparts in the standard model extension. We show that the Lorentz violating parameters in the Higgs sector can be expressed directly in terms of the noncommutative parameter without any background field. The absence of the background field enhances the obtained bounds on the noncommutative parameter from the standard model extension., Comment: 10 pages, to appear in PRD

The nucleon-nucleon scattering in a large magnetic background is considered to find its potential to change the neutrino emissivity of the neutron stars. For this purpose we consider the one-pion-exchange approximation to find the NN cross-section in a background field as large as $10^{15}\texttt{G}-10^{18}\texttt{G}$. We show that the NN cross-section in neutron stars with temperatures in the range 0.1-5 \texttt{MeV} can be changed up to the one order of magnitude with respect to the one in the absence of the magnetic field. In the limit of the soft neutrino emission the neutrino emissivity can be written in terms of the NN scattering amplitude therefore the large magnetic fields can dramatically change the neutrino emissivity of the neutron stars as well., Comment: 21 pages, 5 figures, to appear in PRD

QED based on $\theta$-unexpanded noncomutative space-time in contrast with the noncommutative QED based on $\theta$-expanded U(1) gauge theory via the Seiberg-Witten map, is one-loop renormalizable. Meanwhile it suffers from asymptotic freedom that is not in agreement with the experiment. We show that QED part of $U_\star(3)\times U_\star(1)$ gauge group as an appropriate gauge group for the noncommutative QED+QCD, is not only one-loop renormalizable but also has a $\beta$ function that can be positive, negative and even zero. In fact the $\beta$ function depends on the mixing parameter $\delta_{13}$ as a free parameter and it will be equal to its counterpart in the ordinary QED for $\delta_{13}=0.367\pi$., Comment: 33 pages, 30 figures, to appear in PRD

According to the standard cosmology, near the last scattering surface, the photons scattered via Compton scattering are just linearly polarized and then the primordial circular polarization of the CMB photons is zero. In this work we show that CMB polarization acquires a small degree of circular polarization when a background magnetic field is considered or the quantum electrodynamic sector of standard model is extended by Lorentz-noninvariant operators as well as noncommutativity. The existence of circular polarization for the CMB radiation may be verified during future observation programs and it represents a possible new channel for investigating new physics effects., Comment: 28 pages, v3, Phys. Rev. D 81, 084035 (2010)

We consider the noncommutative standard model based on $SU(3)\times SU(2)\times U(1)$. We study the gauge transformation of right handed neutrino and its direct interaction with photon in the noncommutative space-time. We show that the massive Dirac neutrinos, through the Higgs mechanism, can not accommodate this extension of the standard model; while the massive Majorana neutrinos are consistent with the gauge symmetry of the model. The electromagnetic properties and the dispersion relations for the neutrino in the noncommutative standard model is examined. We also compare the results with the noncommutative standard model based on $U(3)\times U(2)\times U(1) $., Comment: 14 pages, 1 figure, to appear in Phys. Rev. D

We consider Lorentz conserving noncommutative field theory to construct the Lorentz conserving noncommutative standard model based on the gauge group $SU(3)\times SU(2)\times U(1)$. We obtain the enveloping algebra-valued of Higgs field up to the second order of the noncommutativity parameter $\th_{\mu\nu}$. We derive the action at the leading order and find new vertices which are absent in the ordinary Standard Model as well as the minimal noncommutative standard model. We briefly study the phenomenological aspects of the model., Comment: 18 pages, 1 figure, to appear in Phys. Rev. D

We address the problem of finding a system in which there would be measurable quantum gravitational effects. Following standard quantum-field methods, we have calculated the first-order radiative correction of graviton exchange on the binding energy of an electron with an ultra cold superfluid droplet of $^4$He with mass about the Planck mass. For two $^4$He droplets with a mass difference of about one microgram, we show that the relative difference in the binding energies is about one percent., Comment: 5 pages, 2 figures

We extend the non-commutative standard model based on the minimal $SU(3)\times SU(2)\times U(1)$ gauge group to include the interaction of photon with neutrino. We show that, in the gauge invariant manner, only the right handed neutrino can directly couple to the photon. Consequently, we obtain the Feynman rule for the $\gamma\nu\bar\nu$-vertex which does not exist in the minimal extension of non-commutative standard model (mNCSM). We calculate the amplitude for $\gamma\nu\to\gamma\nu$ in both the nonminimal non-commutative standard model (nmNCSM) and the extended version of mNCSM. The obtained cross section grows in the center of mass frame, respectively, as $(\theta_{NC})^2{M}_Z^{-4}E^6$ and $(\theta_{NC})^4E^6$ which can exceed the cross section for $\gamma\nu\to\gamma\gamma\nu$ and $\gamma\nu\to\gamma\nu$ in the high energy limit in the commutative space., Comment: 12 pages, 3 figures, to appear in Phys. Rev. D

We consider the Lorentz invariant non-commutative QED and complete the Feynman rules for the theory up to the order $\theta^2$. In the Lorentz invariant version of the non-commutative QED the particles with fractional charges can be also considered. We show that in the parton model, even at the lowest order, the Bjorken scaling violates as $\sim\theta^2Q^4$., Comment: 9 pages, 1 figure, to appear in Phys. Rev. D

The Klein-Gordon equation with scalar potential is considered. In the Feshbach-Villars representation the annihilation operator for a linear potential is defined and its eigenstates are obtained. Although the energy levels in this case are not equally-spaced, depending on the eigenvalues of the annihilation operator, the states are nearly coherent and squeezed. The relativistic Poschl-Teller potential is introduced. It is shown that its energy levels are equally-spaced. The coherence of time evolution of the eigenstates of the annihilation operator for this potential is evaluated., Comment: 12 pages, 11 figures, to appear in Phys. lett. A

The Bethe-Salpeter equation in non-commutative QED (NCQED) is considered for three-body bound state. We study the non-relativistic limit of this equation in the instantaneous approximation and derive the corresponding Schr\"{o}dinger equation in non-commutative space. It is shown that the experimental data for Helium atom puts an upper bound on the magnitude of the parameter of non-commutativity, $\theta\sim10^{-9}\lambda_e^2$., Comment: 10 pages, 3 figures, to appear in Phys. Rev. D

We derive Spinless Salpeter equation for the positronium using the NRQED Lagrangian. Consequently, we consider the Spinless Salpeter wavefunction instead of the Schrodinger wavefunction to show that the NRQED calculation can be done easier. We also discuss that the singularity of the Spinless Salpeter wavefunction at the origin is necessary to cancel the ultraviolet divergence in the NRQED calculations., Comment: 12 pages, 6 figures

We obtain positronium Hyperfine Splitting owing to the non-commutativity of space and show that, in the leading order, it is proportional to $\theta \alpha^6$ where, $\theta$ is the parameter of non-commutativity. It is also shown that spatial non-commutativity splits the spacing between $n=2$ triplet excited levels $E(2^3S_1)\to E(2^3P_2)$ which provides an experimental test on the non-commutativity of space., Comment: 7 pages, 2 figures, to appear in Phys. Rev. D

Bethe-Salpeter equation in the non-commutative space for a scalar-scalar bound state is considered. It is shown that in the non-relativistic limit, the effect of spatial non-commutativity appears as if there exist a magnetic dipole moment coupled to each particle.