Magnetic domain walls of relic fermions as Dark Energy

We show that relic fermions of the Big Bang can enter a ferromagnetic state if they possess a magnetic moment and satisfy the requirements of Stoner theory of itinerant ferromagnetism. The domain walls of this ferromagnetism can successfully simulate Dark Energy over the observable epoch spanning $\sim 10$ billion years. We obtain conditions on the anomalous magnetic moment of such fermions and their masses. Known neutrinos fail to satisfy the requirements thus pointing to the possibility of a new ultralight sector in Particle Physics.Comment: Essentially same as version 2; to appear in AIP proceedings of PASCOS 200

Graceful exit via monopoles in a theory with O'Raifeartaigh type supersymmetry breaking

We study the stability of supersymmetry breaking metastable vacua and supersymmetric vacua in the presence of solitons. The metastable vacua of supersymmetric QCD and those found elsewhere such as in models based on the SU(5) grand unified group support the existence of topological solitons. The vacua containing such topological defects can become unstable against decay into lower energy configurations. We show for a specific model that a finite region of the available parameter space of couplings becomes disallowed due to the presence of monopoles. In a manner similar to previous studies based on cosmic strings, it is shown that soliton solutions arising in supersymmetric theories can put constraints on the range of allowed values of the couplings arising in the theories. Implications for cosmology are discussed.Comment: 20 pages, 7 figure

Naturalness of parity breaking in a supersymmetric SO(10) model

We consider a supersymmetric SO(10) model which remains renormalisable upto Planck scale. The cosmology of such a model passes through a Left-Right symmetric phase. Potential problems associated with domain walls can be evaded if parity breaking is induced by soft terms when supersymmetry breaks in the hidden sector. The smallness of this breaking permits a brief period of domination by the domain walls ensuring dilution of gravitinos and other unwanted relics. The requirement that domain walls disappear constrains some of the soft parameters of the Higgs potential.Comment: 4 pages, To appear in Proceedings of SUSY06, the 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, 12-17 June 200

Gauged B-L unification and cosmology

We discuss some cosmological implications of low energy gauged B-L symmetry with and without supersymmetry. Generic possibility of leptogenesis from a domain wall driven first order phase transition is shown to be a characteristic of such models.Comment: 6 pages. Talk given at IWTHEP 2007, IIT Roorke

Production and decay rates of excited leptons in a left-right symmetric scenario

We merge two leading Beyond Standard Model scenarios, namely compositeness and left-right symmetry, and probe the resulting collider signatures in the leptonic case. The constraints on composite models for fermions leave open the possibility of vector like excitations of Standard Model (SM) fermions. Here we consider the possibility of low scale left-right gauge symmetry $SU(2)_{R} \times SU(2)_{L} \times U(1)_ {B-L}$, with the simplifying assumption that the right like excited sector of fermions is significantly heavier than the excitations of the left chiral fermions. It is found that the right handed currents still contribute to observable processes, and alter the existing bounds on the scale of compositeness. The cross section times branching ratio of the photon decay channel is strongly depressed, bringing down the exclusion limit of the mass of excited electrons from about 2 TeV to below 1 TeV. On the other hand, cross section times branching ratio of the Z decay channel is significantly enhanced and remains greater than that of the photon channel. We thus propose analyzing the Z decay channel in existing collider data in order to search for signature of left-right symmetry as well as excited leptons with masses above 1 TeV.Comment: 10 figures updated. Incorporated constraints from muon anomalous magnetic moment, and lepton flavour violation processes. Table I adde