9,066 research outputs found
Gravitating tensor monopole in a Lorentz-violating field theory
We present a solution of the coupled Einstein and rank-two antisymmetric
tensor field equations where Lorentz symmetry is spontaneously broken, and we
discuss its observational signatures. Especially, the deflection angles have
important qualitative differences between tensor and scalar monopoles. If a
monopole were to be detected, it would be discriminated whether or not to
correspond to a tensor one. This phenomenon might open up new direction in the
search of Lorentz violation with future astrophysical observations.Comment: 5 pages, 4 figure
Freeze-in Dirac neutrinogenesis: thermal leptonic CP asymmetry
We present a freeze-in realization of the Dirac neutrinogenesis in which the
decaying particle that generates the lepton-number asymmetry is in thermal
equilibrium. As the right-handed Dirac neutrinos are produced non-thermally,
the lepton-number asymmetry is accumulated and partially converted to the
baryon-number asymmetry via the rapid sphaleron transitions. The necessary
CP-violating condition can be fulfilled by a purely thermal kinetic phase from
the wavefunction correction in the lepton-doublet sector, which has been
neglected in most leptogenesis-based setup. Furthermore, this condition
necessitates a preferred flavor basis in which both the charged-lepton and
neutrino Yukawa matrices are non-diagonal. To protect such a proper Yukawa
structure from the basis transformations in flavor space prior to the
electroweak gauge symmetry breaking, we can resort to a plethora of model
buildings aimed at deciphering the non-trivial Yukawa structures.
Interestingly, based on the well-known tri-bimaximal mixing with a minimal
correction from the charged-lepton or neutrino sector, we find that a
simultaneous explanation of the baryon-number asymmetry in the Universe and the
low-energy neutrino oscillation observables can be attributed to the mixing
angle and the CP-violating phase introduced in the minimal correction.Comment: 28 pages and 7 figures; more discussions and one figure added, final
version published in the journa
Alternative mechanism of avoiding the big rip or little rip for a scalar phantom field
Depending on the choice of its potential, the scalar phantom field
(the equation of state parameter ) leads to various catastrophic fates of
the universe including big rip, little rip and other future singularity. For
example, big rip results from the evolution of the phantom field with an
exponential potential and little rip stems from a quadratic potential in
general relativity (GR). By choosing the same potential as in GR, we suggest a
new mechanism to avoid these unexpected fates (big and little rip) in the
inverse-\textit{R} gravity. As a pedagogical illustration, we give an exact
solution where phantom field leads to a power-law evolution of the scale factor
in an exponential type potential. We also find the sufficient condition for a
universe in which the equation of state parameter crosses divide. The
phantom field with different potentials, including quadratic, cubic, quantic,
exponential and logarithmic potentials are studied via numerical calculation in
the inverse-\textit{R} gravity with correction. The singularity is
avoidable under all these potentials. Hence, we conclude that the avoidance of
big or little rip is hardly dependent on special potential.Comment: 9 pages,6 figure
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