43 research outputs found
Neutrinos that violate CPT, and the experiments that love them
Recently we proposed a framework for explaining the observed evidence for
neutrino oscillations without enlarging the neutrino sector, by introducing CPT
violating Dirac masses for the neutrinos. In this paper we continue the
exploration of the phenomenology of CPT violation in the neutrino sector. We
show that our CPT violating model fits the existing SuperKamiokande data at
least as well as the standard atmospheric neutrino oscillation models. We
discuss the challenge of measuring CP violation in a neutrino sector that also
violates CPT. We point out that the proposed off-axis extension of MINOS looks
especially promising in this regard. Finally, we describe a method to compute
CPT violating neutrino effects by mocking them up with analog matter effects.Comment: 17 pages, 3 eps figure
Self-accelerating solutions of scalar-tensor gravity
Scalar-tensor gravity is the simplest and best understood modification of
general relativity, consisting of a real scalar field coupled directly to the
Ricci scalar curvature. Models of this type have self-accelerating solutions.
In an example inspired by string dilaton couplings, scalar-tensor gravity
coupled to ordinary matter exhibits a de Sitter type expansion, even in the
presence of a {\it negative} cosmological constant whose magnitude exceeds that
of the matter density. This unusual behavior does not require phantoms, ghosts
or other exotic sources. More generally, we show that any expansion history can
be interpreted as arising partly or entirely from scalar-tensor gravity. To
distinguish any quintessence or inflation model from its scalar-tensor
variants, we use the fact that scalar-tensor models imply deviations of the
post-Newtonian parameters of general relativity, and time variation of the
Newton's gravitational coupling . We emphasize that next-generation probes
of modified GR and the time variation of are an essential complement to
dark energy probes based on luminosity-distance measurements.Comment: 14 pages, 3 figure
Slow roll in simple non-canonical inflation
We consider inflation using a class of non-canonical Lagrangians for which
the modification to the kinetic term depends on the field, but not its
derivatives. We generalize the standard Hubble slow roll expansion to the
non-canonical case and derive expressions for observables in terms of the
generalized slow roll parameters. We apply the general results to the
illustrative case of ``Slinky'' inflation, which has a simple, exactly
solvable, non-canonical representation. However, when transformed into a
canonical basis, Slinky inflation consists of a field oscillating on a
multi-valued potential. We calculate the power spectrum of curvature
perturbations for Slinky inflation directly in the non-canonical basis, and
show that the spectrum is approximately a power law on large scales, with a
``blue'' power spectrum. On small scales, the power spectrum exhibits strong
oscillatory behavior. This is an example of a model in which the widely used
solution of Garriga and Mukhanov gives the wrong answer for the power spectrum.Comment: 9 pages, LaTeX, four figures. (V2: minor changes to text. Version
submitted to JCAP.
Implications of a Massless Neutralino for Neutrino Physics
We consider the phenomenological implications of a soft SUSY breaking term BN
at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed
neutrino field). In models with a massless (or nearly massless) neutralino,
such a term will give rise through the see-saw mechanism to new contributions
to the mass matrix of the light neutrinos.
We treat the massless neutralino as an (almost) sterile neutrino and find
that its mass depends on the square of the soft SUSY breaking scale, with
interesting consequences for neutrino physics. We also show that, although it
requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not
experimentally excluded. The implications of this scenario for neutrino physics
are discussed.Comment: 14 pages, latex, no figure
Cosmological Implications of a Scale Invariant Standard Model
We generalize the standard model of particle physics such it displays global
scale invariance. The gravitational action is also suitably modified such that
it respects this symmetry. This model is interesting since the cosmological
constant term is absent in the action. We find that the scale symmetry is
broken by the recently introduced cosmological symmetry breaking mechanism.
This simultaneously generates all the dimensionful parameters such as the
Newton's gravitational constant, the particle masses and the vacuum or dark
energy. We find that in its simplest version the model predicts the Higgs mass
to be very small, which is ruled out experimentally. We further generalize the
model such that it displays local scale invariance. In this case the Higgs
particle disappears from the particle spectrum and instead we find a very
massive vector boson. Hence the model gives a consistent description of
particle physics phenomenology as well as fits the cosmological dark energy.Comment: 12 pages, no figure
Left-right symmetry in 5D and neutrino mass in TeV scale gravity models
We construct a left-right symmetric model based on the gauge group
in five dimensions where both the
gauge bosons and fermions reside in all five dimensions. The orbifold boundary
conditions are used not only to break the gauge symmetry down to but also to ``project'' the right handed neutrino out
of the zero mode part of the spectrum, providing a new way to understand the
small neutrino masses without adding (singlet) bulk neutrinos. This formulation
of the left-right model has also two new features: (i) it avoids most existing
phenomenological bounds on the scale of the right handed boson allowing
for the possibility that the right handed gauge bosons could have masses under
a TeV, and (ii) it predicts a stable lepton with mass of order of the inverse
radius of the fifth dimension.Comment: 20 pages; some new materials and references adde