B-L Cosmic strings and Baryogenesis

Cosmic strings arising from breaking of the $U(1)_{B-L}$ gauge symmetry that occurs in a wide variety of unified models can carry zero modes of heavy Majorana neutrinos. Decaying and/or repeatedly self-interacting closed loops of these ``$B-L$'' cosmic strings can be a non-thermal source of heavy right-handed Majorana neutrinos whose decay can contribute to the observed baryon asymmetry of the Universe (BAU) via the leptogenesis route. The $B-L$ cosmic strings are expected in GUT models such as SO(10), where they can be formed at an intermediate stage of symmetry breaking well below the GUT scale $\sim 10^{16}$ GeV; such light strings are not excluded by the CMB anisotropy data and may well exist. We estimate the contribution of $B-L$ cosmic string loops to the baryon-to-photon ratio of the Universe in the light of current knowledge on neutrino masses and mixings implied by atmospheric and solar neutrino measurements. We find that $B-L$ cosmic string loops can contribute significantly to the BAU for $U(1)_{B-L}$ symmetry breaking scale \eta_{B-L}\gsim 1.7\times 10^{11}\gev. At the same time, in order for the contribution of decaying $B-L$ cosmic string loops not to exceed the observed baryon-to-photon ratio inferred from the recent WMAP results, the lightest heavy right-handed Majorana neutrino mass $M_1$ must satisfy the constraint M_1 \leq 2.4 \times 10^{12}(\eta_{B-L}/10^{13}\gev)^{1/2}\gev. This may have interesting implications for the associated Yukawa couplings in the heavy neutrino sector and consequently for the light neutrino masses generated through see-saw mechanism.Comment: match with the published versio

Soliton-fermion systems and stabilised vortex loops

In several self-coupled quantum field theories when treated in semi-classical limit one obtains solitonic solutions determined by topology of the boundary conditions. Such solutions, e.g. magnetic monopole in unified theories \cite{Hooft1974} \cite{Polyakov1974} or the skyrme model of hadrons have been proposed as possible non-perturbative bound states which remain stable due to topological quantum numbers. Furthermore when fermions are introduced, under certain conditions one obtains zero-energy solutions \cite{Vega1978}\cite{Jackiw1981} for the Dirac equations localised on the soliton. An implication of such zero-modes is induced fermion number \cite{Jackiw1977} carried by the soliton.Comment: 4 pages, presented at the 17th DAE-BRNS HEP symposium held at IIT Kharagpur, Indi

Arbitrary Lagrangian–Eulerian finite element method for curved and deforming surfaces: I. General theory and application to fluid interfaces

An arbitrary Lagrangian–Eulerian (ALE) finite element method for arbitrarily curved and deforming two-dimensional materials and interfaces is presented here. An ALE theory is developed by endowing the surface with a mesh whose in-plane velocity need not depend on the in-plane material velocity, and can be specified arbitrarily. A finite element implementation of the theory is formulated and applied to curved and deforming surfaces with in-plane incompressible flows. Numerical inf–sup instabilities associated with in-plane incompressibility are removed by locally projecting the surface tension onto a discontinuous space of piecewise linear functions. The general isoparametric finite element method, based on an arbitrary surface parametrization with curvilinear coordinates, is tested and validated against several numerical benchmarks. A new physical insight is obtained by applying the ALE developments to cylindrical fluid films, which are computationally and analytically found to be stable to non-axisymmetric perturbations, and unstable with respect to long-wavelength axisymmetric perturbations when their length exceeds their circumference. A Lagrangian scheme is attained as a special case of the ALE formulation. Though unable to model fluid films with sustained shear flows, the Lagrangian scheme is validated by reproducing the cylindrical instability. However, relative to the ALE results, the Lagrangian simulations are found to have spatially unresolved regions with few nodes, and thus larger errors

Synthesis and characterization of spin frustrated Fe doped LiCrO2

LiCrO2 and Fe doped LiCrO2 are prepared by solid state reaction method using LiCO3, Cr2O3, and Fe2O3. From XRD data analysis we could confirm the phase purity of all the samples; LiCrO2, LiCr0.98Fe0.02O2, and LiCr0.95Fe0.05O2. All the three samples show dispersion in dielectric constant (år) and dielectric loss factor (tan ä) values. The dielectric constant as a function of frequency at different bias voltage has also been studied. Magnetization measurement for LiCrO2 using a SQUID magnetometer in a constant magnetic field of 100 Oe under zero field cooled and field cooled condition show the antiferromagnetic transition temperature, TN ~ 64K. The UV visible plot reveals the slightly increase in band gap due to doping

Gauged B−LB-L symmetry and baryogenesis via leptogenesis at TeV scale

It is shown that the requirement of preservation of baryon asymmetry does not rule out a scale for leptogenesis as low as 10 TeV. The conclusions are compatible with see-saw mechanism if for example the pivot mass scale for neutrinos is $\approx 10^{-2}$ that of the charged leptons. We explore the parameter space $\tilde{m}_1$-$M_1$ of relevant light and heavy neutrino masses by solving Boltzmann equations. A viable scenario for obtaining baryogenesis in this way is presented in the context of gauged $B-L$ symmetry.Comment: 15 pages, 4 figures, references added, match with journal versio