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Riazuddin

Publications and source records attributed to Riazuddin.

At least 19 recordsLinked to original sources
arXiv2012

Parity anomaly in Dirac equation in (1+2) dimensions, quantum electrodynamics and pair production

It is shown that parity operator plays an interesting role in Dirac equation in (1+2) dimensions and can be used for defining chiral currents. It is shown that the "anomalous" current induced by an external gauge field can be related to the anomalous divergence of an axial vector current which arises due to quantum radiative corrections provided by triangular loop Feynman diagrams in analogy with the corresponding axial anomaly in (1+3) dimensions. It is shown that the non-conservation of "chiral charge" due to anomaly is related with the topological Chern-Simons charge. As an application pair creation of massless fermions is discussed in electric field.

hep-ph↗
arXiv2012

Second-class current effects from isospin breaking in tau-->omega pi nu_tau

Second-class weak currents can in the standard model be induced by chiral symmetry breaking. In the specific case of the decay tau-->omega pi nu_tau, dominated by the first-class vector current with the rho quantum numbers, such effects would manifest themselves by small axial vector (or, generally, non-vector) contributions to the decay rate. We present an attempt to estimate such effects, based on a vector and axial-vector dominance model of the relevant matrix elements supplemented by omega-rho mixing. We also give an indication on the amplitude directly mediated by b_1(1235)-->omega pi, in principle also allowed in the standard model by isotopic spin violation.

hep-ph↗
arXiv2011

Spin-orbit splittings in heavy-light mesons and Dirac equation

The spin-orbit splitting in heavy-light mesons is seen to be suppressed experimentally. It is shown that it can be understood qualitatively in the frame work of Dirac theory. An alternative derivation of a relativistic dynamical symmetry for the Dirac Hamiltonian, which suppresses spin orbit splitting, is also given. However it is shown that such a symmetry is not needed since the spin-orbit splitting in Dirac theory with Coulomb like potential (as is the case for the one gluon exchange potential in pQCD) is small anyway.

hep-ph↗
arXiv2011

$\sin{\theta}_{13}$ and neutrino mass matrix with an approximate flavor symmetry

For a neutrino mass matrix whose texture has an approximate flavor symmetry and where one has near degenerate neutrino mass, it is shown that the tribimaximal values for atmospheric angle $\sin^{2}{\theta_{23}}=1/2$ and solar angle $\sin^{2}{\theta_{12}}=1/3$ can be maintained even when the reactor angle $\theta_{13}\neq0$. The non zero $\sin\theta_{13}$ implies approximate $\nu_{\mu}\rightarrow-\nu_{\tau}$ symmetry instead of $\nu_{\mu}\rightarrow\nu_{\tau}$ symmetry.

hep-ph↗
arXiv2011

Dynamical Symmetries of Dirac Hamiltonian

Several dynamical symmetries of the Dirac Hamiltonian are reviewed in a systematic manner and the conditions under which such symmetries hold. These include relativistic spin and orbital angular momentum symmetries, SO(4)\times SU_{\sigma}(2) symmetry for the Dirac Hydrogen atom, SU(3)\times SU_{\sigma}(2) symmetry for the relativistic simple harmonic oscillator. The energy spectrum in each case is calculated from group-theoretic considerations.

hep-ph↗
arXiv2011

Dirac equation for quasi-particles in graphene in an external electromagnetic field and chiral anomaly

There is evidence for existence of massless Dirac quasi-particles in graphene, which satisfy Dirac equation in (1+2) dimensions near the so called Dirac points which lie at the corners at the graphene's brilluoin zone. It is shown that parity operator in (1+2) dimensions play an interesting role and can be used for defining conserved chiral currents [there is no gamma^5 in (1+2) dimensions]. It is shown that the "anomalous" current induced by an external gauge field can be related to the anomalous divergence of an axial vector current which arises due to quantum radiative corrections provided by triangular loop Feynman diagrams in analogy with the corresponding axial anomaly in (1+3) dimensions.

cond-mat.mes-hall↗
arXiv2011

On the branching ratio of the "second class" tau --> eta' pi nu_tau decay

We present an assessment of the standard model expectations for the branching ratio of the isotopic spin and G-parity violating decay tau --> eta' pi nu_tau. The estimate is based on a vector and scalar meson dominance parametrization of the relevant form factors, that explicitly accounts for pi^0-eta-eta' mixing. The numerical results obtained in this framework indicate a branching ratio one order of magnitude (or more) below the current experimental limit, and suggest the possibility of evidencing some novel interaction in high statistics studies of this decay.

hep-ph↗
arXiv2010

On meson dominance in the `second class' tau \to eta pi nu_tau decay

Motivated by recent estimates of the isospin-violating process tau \to eta pi nu_tau, mostly relying on the rho and a_0 dominance of the relevant form factors near threshold, we present an assessment for the branching ratio that accounts for additional, potential, effects from the lowest radial excitations rho(1450) and a_0(1450), respectively, also lying in the decay phase space.

hep-ph↗
arXiv2010

$(L_e-L_{\mu}-L_{\tau})$ discrete symmetry for heavy right-handed neutrinos and degenerate leptogenesis

The degenerate leptogenesis is studied when the degeneracy in two of the heavy right-handed neutrinos [the third one is irrelevant if $\mu -\tau $ symmetry is assumed] is due to $\bar{L}\equiv (L_{e}-L_{\mu}-L_{\tau}) $ discrete symmetry. It is shown that a sizeable leptogenesis asymmetry $(\epsilon \succsim 10^{-6}) $ is possible. The level of degeneracy required also predicts the Majorana phase needed for the asymmetry. Since it is the same phase, which appears in the double $\beta $% -decay and this prediction is testable. Implication of non-zero reactor angle $\theta_{13}$ are discussed. It is shown that the contribution from $% \sin ^{2}\theta_{13}$ to leptogenesis asymmetry parameter may even dominate.An accurate measument of $\sin ^{2}\theta_{13}$ would have important implications for the mass degeneracy of heavy right-handed neutrinos.

hep-ph↗
arXiv2008

Tribimaximal mixing and leptogenesis in a seesaw model

It is pointed out that if a neutrino mass matrix for right-handed neutrinos in seesaw mechanism has mu -tau symmetry and total lepton number L_{e}+L_{μ}+L_τ remains constant (not zero), exact tribimaximal neutrino mixing in this sector is produced. The same follows for the effective Majorana light neutrino mass matrix provided that Yukawa couplings (multiplied by the corresponding Higgs vacuum expectation values) in Dirac mass matrix satisfy some constraints which in general implies zero leptongenesis asymmetry. However this can be avoided when two of the heavy right-hand neutrinos [the third one is irrelevant when mu -tau symmetry is assumed] are (nearly) degenerate.

hep-ph↗
arXiv2008

Dirac equation for quasi-particles in graphene and quantum field theory of their Coulomb interaction

There is evidence for existence of massless Dirac quasi-particles in graphene, which satisfy Dirac equation in (1+2) dimensions near the so called Dirac points which lie at the corners at the graphene's brilluoin zone. We revisit the derivation of Dirac equation in (1+2) dimensions obeyed by quasiparticles in graphene near the Dirac points. It is shown that parity operator in (1+2) dimensions play an interesting role and can be used for defining "conserved" currents resulting from the underlying Lagrangian for Dirac quasi-particles in graphene which is shown to have U_{A}(1)*U_{B}(1) symmetry. Further the quantum field theory (QFT) of Coulomb interaction of 2D graphene is developed and applied to vacuum polarization and electron self energy and the renormalization of the effective coupling g of this interaction and Fermi velocity $v_{f}$ which has important implications in the renormalization group analysis of g and v_{f}.

cond-mat.mes-hall↗
arXiv2008

$SU_{L}(4)\times U(1)$ model for electroweak unification and sterile neutrinos

Some of basic problems in neutrino physics such as new energy scales, the enormous gap between neutrino masses and the lightest charged fermion mass, possible existance of sterile neutrinos in eV mass range are studied in the local gauge group $SU_{L}(4)\times U(1)$ for electroweak unification, which does not contain fermions with exotic electric charges. It is shown that neutrino mass spectrum can be decoupled from that of the other fermions. Further normal seesaw mechanism for neutrinos, with right handed neutrino Majorana masses to be of order $M\gg M_{\text{weak}}$ as well a new eV-scale can be accomodated. The eV-scale seesaw may manifest itself in experiments like Liquid Scintilation Neutrino Detector (LSND) and MiniBooNE (MB) experimental results and future neutrino experiments.

hep-ph↗
arXiv2007

An SU(3) symmetry for light neutrinos

It is proposed that light neutrinos form a triplet in a global SU(3) symmetry in mass eigenstate basis. Assuming that the SU(3)symmetry is broken in the direction (-alambda_{3}+frac{b}/{sqrt{3}}lambda_{8}), and after going to the flavor basis we predict atmospheric mixing angle, sin ^{2}theta_{23}=0.5 and sin theta_{13}=0 if nu_{mu}-nu_{tau} symmetry is assumed. In the flavor basis the diagonal part of matrix coefficient of b (dominant part) is found to transform like (lambda_{3}+frac{1}/{sqrt{3}}lambda_{8}). Imposing the same on matrix coefficient of $a$ fixes solar mixing angle,sin ^{2}theta _{12}=frac{1}{3}. Implications for neutrinoless double beta-decay are discussed.

hep-ph↗
arXiv2006

Branching Ratio and CP-asymmetry for B-> 1^{1}P_{1}gamma decays

We calculate the branching ratios for B_{d}^{0}->(b_{1},h_{1})gamma at next-to-leading order (NLO) of alpha_{s} where b_{1} and h_{1} are the corresponding radially excited axial vector mesons of rho and omega respectively. Using the SU(3)symmetry for the form factor, the branching ratio for B_{d}^{0}->(b_{1},h_{1})gamma is expressed in terms of the branching ratio of the B_{d}^{0}-> K_{1}gamma and it is found to be B(B_{d}^{0}->b_{1}gamma)=0.71* 10^{-6} and B(B_{d}^{0}-> h_{1}gamma) =0.74*10^{-6}. We also calculate direct CP asymmetry for these decays and find, in confirmity with the observations made in the literature, that the hard spectator contributions significantely reduces the asymmetry arising from the vertex corrections alone. The value of CP-asymmetry is 10% and is negative like rho and omega in the Standard Model.

hep-ph↗
arXiv2005

Neutrino flavor mixing in an SU(3) symmetry for light neutrinos

It is proposed that light neutrinos form a triplet in a global SU(3) flavor symmetry. Within this framework, a symmetry principle predicts sin^2 theta_{23}=0.5 and gives the so called inverted neutrino mass hierarchy, theta _{13}=0 and a small deviation from pi/4 for theta_{12}.

hep-ph↗
arXiv2004

SU_L(4) x U(1) model for electroweak unification

After some general remarks about SU_L(4) electroweak unification, the model is extended to SU_L(4)xU_X(1) to accomodate fractionally charged quarks. The unification scale is expected to be in TeV region. A right-handed Majorana neutrino along with known lepton are put in the fundamental representation of SU_L(4) with Y_X=0. The see-saw mechanism for neutrino masses and flavor mixing in neutrino sector is a natural feature of the model. The lepton number violating processes can occure through dilepton gauge bosons contained in the model.

hep-ph↗
arXiv2004

Form factors and branching ratio for the B -> l nu gamma decay

Form factors parameterizing radiative leptonic decays of heavy mesons $% (B^{+}\to \gamma l^{+}\nu_{l}) $ for photon energy are computed in the language of dispersion relation. The contributing states to the absorptive part in the dispersion relation are the multiparticle continum, estimated by quark triangle graph and resonances with quantum numbers $1^{-}$ and $1^{+}$ which includes $B^{*}$ and $B_{A}^{*}$ and thier radial excitations, which model the higher state contributions. Constraints provided by the asymptotic behavior of the structure dependent amplitude, Ward Identities and gauge invariance are used to provide useful information for parameters needed. The couplings $g_{BB^{*}\gamma}$ and $% f_{BB_{A}^{*}\gamma}$ are predicted if we restrict to first radial excitation; otherwise using these as an input the radiative decay coupling constants for radial excitations are predicted. The value of the branching ratio for the process $B^{+}\to \gamma \mu ^{+}\nu_{\mu}$ is found to be in the range $0.5\times 10^{-6}$. A detailed comparison is given with other approaches.

hep-ph↗