12 research outputs found
The (ir)Relevance of Initial Conditions in Soft Leptogenesis
We explore how the initial conditions affect the final lepton asymmetry in
Soft Leptogenesis. It has been usually assumed that the initial state is a
statistical mixture of sterile sneutrinos and anti-sneutrinos with equal
abundances. We calculate the lepton asymmetry due to the most general initial
mixture. The usually assumed equal mixture produces a small, but sufficient,
lepton asymmetry which is proportional to the ratio of the supersymmetry
breaking scale over the Majorana scale. A more generic mixture, still with
equal contents of sneutrinos and anti sneutrinos, yields an unsuppressed lepton
asymmetry. Mixtures of non equal contents of sneutrinos and anti sneutrinos
result in a large lepton asymmetry too. While these results establish the
robustness of Soft Leptogenesis and other mixing based mechanisms, they also
expose their lack of predictive power.Comment: v1: 12 pages; v2: typos corrected; v3: published version with new
discussions and reference
Nonlinear wave dynamics in honeycomb lattices
We study the nonlinear dynamics of wave packets in honeycomb lattices, and
show that, in quasi-1D configurations, the waves propagating in the lattice can
be separated into left-moving and right-moving waves, and any wave packet
composed of left (or right) movers only does not change its intensity structure
in spite of the nonlinear evolution of its phase. We show that the propagation
of a general wave packet can be described, within a good approximation, as a
superposition of left and right moving self-similar (nonlinear) solutions.
Finally, we find that Klein tunneling is not suppressed due to nonlinearity
Breakdown of Dirac Dynamics in Honeycomb Lattices due to Nonlinear Interactions
We study the dynamics of coherent waves in nonlinear honeycomb lattices and
show that nonlinearity breaks down the Dirac dynamics. As an example, we
demonstrate that even a weak nonlinearity has major qualitative effects one of
the hallmarks of honeycomb lattices: conical diffraction. Under linear
conditions, a circular input wave-packet associated with the Dirac point
evolves into a ring, but even a weak nonlinearity alters the evolution such
that the emerging beam possesses triangular symmetry, and populates Bloch modes
outside of the Dirac cone region. Our results are presented in the context of
optics, but we propose a scheme to observe equivalent phenomena in
Bose-Einstein condensates
Pseudospin and nonlinear conical diffraction in Lieb lattices
We study linear and nonlinear wave dynamics in the Lieb lattice, in the vicinity of an intersection point between two conical bands and a flat band. We define a pseudospin operator and derive a nonlinear equation for spin-1 waves, analogous to the spin-1/2 nonlinear Dirac equation. We then study the dynamics of wave packets that are associated with different pseudospin states, and find that they are distinguished by their linear and nonlinear conical diffraction patterns
Flat band states: disorder and nonlinearity
We study the critical behavior of Anderson localized modes near intersecting flat and dispersive bands in the quasi-one-dimensional diamond ladder with weak diagonal disorder W. The localization length ξ of the flat band states scales with disorder as ξ∼W-γ, with γ≈1.3, in contrast to the dispersive bands with γ=2. A small fraction of dispersive modes mixed with the flat band states is responsible for the unusual scaling. Anderson localization is therefore controlled by two different length scales. Nonlinearity can produce qualitatively different wave spreading regimes, from enhanced expansion to resonant tunneling and self-trapping
Prefect Klein tunneling in anisotropic graphene-like photonic lattices
We study the scattering of waves off a potential step in deformed honeycomb
lattices. For small deformations below a critical value, perfect Klein
tunneling is obtained. This means that a potential step in any direction
transmits waves at normal incidence with unit transmission probability,
irrespective of the details of the potential. Beyond the critical deformation,
a gap in the spectrum is formed, and a potential step in the deformation
direction reflects all normal-incidence waves, exhibiting a dramatic transition
form unit transmission to total reflection. These phenomena are generic to
honeycomb lattice systems, and apply to electromagnetic waves in photonic
lattices, quasi-particles in graphene, cold atoms in optical lattices
PT-symmetry in honeycomb photonic lattices
We apply gain/loss to honeycomb photonic lattices and show that the
dispersion relation is identical to tachyons - particles with imaginary mass
that travel faster than the speed of light. This is accompanied by PT-symmetry
breaking in this structure. We further show that the PT-symmetry can be
restored by deforming the lattice
Hiding the Higgs at the LHC
We study a simple extension of the standard model where scalar singlets that
mix with the Higgs doublet are added. This modification to the standard model
could have a significant impact on Higgs searches at the LHC. The Higgs doublet
is not a mass eigenstate and therefore the expected nice peak of the standard
model Higgs disappears. We analyze this scenario finding the required
properties of the singlets in order to make the Higgs "invisible" at the LHC.
In some part of the parameter space even one singlet could make the discovery
of the SM Higgs problematic. In other parts, the Higgs can be discovered even
in the presence of many singlets.Comment: 9 pages, 1 figure. V2- References added. V3- Several examples and one
fig. adde