2,102 research outputs found
Lepton Flavor Violation without Supersymmetry
We study the lepton flavor violating (LFV) processes mu -> e gamma, mu -> 3e,
and mu -> e conversion in nuclei in the left-right symmetric model without
supersymmetry and perform the first complete computation of the LFV branching
ratios B(mu -> f) to leading non-trivial order in the ratio of left- and
right-handed symmetry breaking scales. To this order, B(mu -> e gamma) and B(mu
-> e) are governed by the same combination of LFV violating couplings, and
their ratio is naturally of order unity. We also find B(mu -> 3 e)/B(mu -> e)
\sim 100 under slightly stronger assumptions. Existing limits on the branching
ratios already substantially constrain mass splittings and/or mixings in the
heavy neutrino sector. When combined with future collider studies and precision
electroweak measurements, improved limits on LFV processes will test the
viability of low-scale, non-supersymmetric LFV scenarios.Comment: 24 pages, 7 figures, 2 table
Burgers turbulence with pressure
The randomly driven Burgers equation with pressure is considered as a 1D
model of strong turbulence of compressible fluid. It is shown that infinitely
small pressure provides a finite effect on the velocity and density statistics
and this case therefore is qualitatively different from turbulence without
pressure. We establish the corresponding operator product expansion and predict
the intermittent velocity- difference and mass-difference PDFs. We then apply
the developed methods to the statistics of a passive scalar advected by the
Burgers field.Comment: 4 pages, revte
Gravitational Uncertainty and Black Hole Remnants
Possible existence of black holes remnants provides a suitable candidates for
dark matter. In this paper we study the possibility of existence for such
remnants. We consider quantum gravitational induced corrections of black hole's
entropy and temperature to investigate the possibility of such relics.
Observational scheme for detection of these remnants and their cosmological
constraints are discussed.Comment: 17 pages, 6 figure
Reflection coefficient for superresonant scattering
We investigate superresonant scattering of acoustic disturbances from a
rotating acoustic black hole in the low frequency range. We derive an
expression for the reflection coefficient, exhibiting its frequency dependence
in this regime.Comment: 7 page
Notes on Ghost Dark Energy
We study a phenomenological dark energy model which is rooted in the
Veneziano ghost of QCD. In this dark energy model, the energy density of dark
energy is proportional to Hubble parameter and the proportional coefficient is
of the order , where is the mass scale of QCD.
The universe has a de Sitter phase at late time and begins to accelerate at
redshift around . We also fit this model and give the
constraints on model parameters, with current observational data including
SnIa, BAO, CMB, BBN and Hubble parameter data. We find that the squared sound
speed of the dark energy is negative, which may cause an instability. We also
study the cosmological evolution of the dark energy with interaction with cold
dark matter.Comment: 20 pages,10 figures,Correct some typos and add new reference
Massive vector fields on the Schwarzschild spacetime: quasinormal modes and bound states
We study the propagation of a massive vector or Proca field on the
Schwarzschild spacetime. The field equations are reduced to a one-dimensional
wave equation for the odd-parity part of the field and two coupled equations
for the even-parity part of the field. We use numerical techniques based on
solving (scalar or matrix-valued) three-term recurrence relations to compute
the spectra of both quasi-normal modes and quasi-bound states, which have no
massless analogue, complemented in the latter case by a forward-integration
method. We study the radial equations analytically in both the near-horizon and
far-field regions and use a matching procedure to compute the associated
spectra in the small-mass limit. Finally, we comment on extending our results
to the Kerr geometry and its phenomenological relevance for hidden photons
arising e.g. in string theory compactifications.Comment: 15 pages, 8 figures; minor corrections, to be published in Phys. Rev.
A few provoking relations between dark energy, dark matter and pions
I present three relations, striking in their simplicity and fundamental
appearance. The first one connects the Compton wavelength of a pion and the
dark energy density of the Universe; the second one connects Compton wavelength
of a pion and the mass distribution of non-baryonic dark matter in a Galaxy;
the third one relates mass of a pion to fundamental physical constants and
cosmological parameters. All these relations are in excellent numerical
agreement with observations
Tests of Lorentz and CPT symmetry with hadrons and nuclei
We explore the breaking of Lorentz and CPT invariance in strong interactions at low energy in the framework of chiral perturbation theory. Starting from the set of Lorentz-violating operators of mass-dimension five with quark and gluon fields, we construct the effective chiral Lagrangian with hadronic and electromagnetic interactions induced by these operators. We develop the power-counting scheme and discuss loop diagrams and the one-pion-exchange nucleon-nucleon potential. The effective chiral Lagrangian is the basis for calculations of low-energy observables with hadronic degrees of freedom. As examples, we consider clock-comparison experiments with nuclei and spin-precession experiments with nucleons in storage rings. We derive strict limits on the dimension-five tensors that quantify Lorentz and CPT violation
Cosmological Hysteresis and the Cyclic Universe
A Universe filled with a homogeneous scalar field exhibits `Cosmological
hysteresis'. Cosmological hysteresis is caused by the asymmetry in the equation
of state during expansion and contraction. This asymmetry results in the
formation of a hysteresis loop: , whose value can be non-vanishing
during each oscillatory cycle. For flat potentials, a negative value of the
hysteresis loop leads to the increase in amplitude of consecutive cycles and to
a universe with older and larger successive cycles. Such a universe appears to
possess an arrow of time even though entropy production is absent and all of
the equations respect time-reversal symmetry ! Cosmological hysteresis appears
to be widespread and exists for a large class of scalar field potentials and
mechanisms for making the universe bounce. For steep potentials, the value of
the hysteresis loop can be positive as well as negative. The expansion factor
in this case displays quasi-periodic behaviour in which successive cycles can
be both larger as well as smaller than previous ones. This quasi-regular
pattern resembles the phenomenon of BEATS displayed by acoustic systems.
Remarkably, the expression relating the increase/decrease in oscillatory cycles
to the quantum of hysteresis appears to be model independent. The cyclic
scenario is extended to spatially anisotropic models and it is shown that the
anisotropy density decreases during successive cycles if the hysteresis loop is
negative.Comment: 31 pages, 8 figures. Matches version published in Phys Rev D85,
123542 (2012
Nonlinear turbulent magnetic diffusion and effective drift velocity of large-scale magnetic field in a two-dimensional magnetohydrodynamic turbulence
We study a nonlinear quenching of turbulent magnetic diffusion and effective
drift velocity of large-scale magnetic field in a developed two-dimensional MHD
turbulence at large magnetic Reynolds numbers. We show that transport of the
mean-square magnetic potential strongly changes quenching of turbulent magnetic
diffusion. In particularly, the catastrophic quenching of turbulent magnetic
diffusion does not occur for the large-scale magnetic fields when a divergence of the flux of the mean-square magnetic
potential is not zero, where is the equipartition mean magnetic
field determined by the turbulent kinetic energy and Rm is the magnetic
Reynolds number. In this case the quenching of turbulent magnetic diffusion is
independent of magnetic Reynolds number. The situation is similar to
three-dimensional MHD turbulence at large magnetic Reynolds numbers whereby the
catastrophic quenching of the alpha effect does not occur when a divergence of
the flux of the small-scale magnetic helicity is not zero.Comment: 8 pages, Physical Review E, in pres
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