6,752 research outputs found
Constraints from Type IA Supernovae on {\lambda}-CDM Model in Randers-Finsler Space
Gravitational field equations in Randers-Finsler space of approximate Berwald
type are investigated. A modified Friedmann equation and a new luminosity
distance-redshift relation is proposed. A best-fit to the Type Ia supernovae
(SNe) observations yields that the in the -CDM
model is suppressed to almost zero. This fact indicates that the astronomical
observations on the Type Ia SNe can be described well without invoking any form
of dark energy. The best-fit age of the universe is given. It is in agreement
with the age of our galaxy.Comment: 14 pages, 3 figure
Cosmological model with local symmetry of very special relativity and constraints on it from supernovae
Based on Cohen \& Glashow's very special relativity [A. G. Cohen and S. L.
Glashow, Phys. Rev. Lett. {\bf 97} (2006) 021601], we propose an anisotropic
modification to the Friedmann-Robertson-Walker (FRW) line element. An
arbitrarily oriented 1-form is introduced and the FRW spacetime becomes of the
Randers-Finsler type. The 1-form picks out a privileged axis in the universe.
Thus, the cosmological redshift as well as the Hubble diagram of the type Ia
supernovae (SNe Ia) becomes anisotropic. By directly analyzing the Union2
compilation, we obtain the privileged axis pointing to
(). This privileged axis is close to those obtained by
comparing the best-fit Hubble diagrams in pairs of hemispheres. It should be
noticed that the result is consistent with isotropy at the level
since the anisotropic magnitude is .Comment: 13 pages, 2 figures. Published at EPJC(2013
Kinetic Ballooning Mode Under Steep Gradient: High Order Eigenstates and Mode Structure Parity Transition
The existence of kinetic ballooning mode (KBM) high order (non-ground)
eigenstates for tokamak plasmas with steep gradient is demonstrated via
gyrokinetic electromagnetic eigenvalue solutions, which reveals that eigenmode
parity transition is an intrinsic property of electromagnetic plasmas. The
eigenstates with quantum number for ground state and for
non-ground states are found to coexist and the most unstable one can be the
high order states (). The conventional KBM is the state. It is
shown that the KBM has the same mode structure parity as the
micro-tearing mode (MTM). In contrast to the MTM, the KBM can be driven
by pressure gradient even without collisions and electron temperature gradient.
The relevance between various eigenstates of KBM under steep gradient and edge
plasma physics is discussed.Comment: 6 pages, 6 figure
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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