529 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
Locality of not-so-weak coloring
Many graph problems are locally checkable: a solution is globally feasible if
it looks valid in all constant-radius neighborhoods. This idea is formalized in
the concept of locally checkable labelings (LCLs), introduced by Naor and
Stockmeyer (1995). Recently, Chang et al. (2016) showed that in bounded-degree
graphs, every LCL problem belongs to one of the following classes:
- "Easy": solvable in rounds with both deterministic and
randomized distributed algorithms.
- "Hard": requires at least rounds with deterministic and
rounds with randomized distributed algorithms.
Hence for any parameterized LCL problem, when we move from local problems
towards global problems, there is some point at which complexity suddenly jumps
from easy to hard. For example, for vertex coloring in -regular graphs it is
now known that this jump is at precisely colors: coloring with colors
is easy, while coloring with colors is hard.
However, it is currently poorly understood where this jump takes place when
one looks at defective colorings. To study this question, we define -partial
-coloring as follows: nodes are labeled with numbers between and ,
and every node is incident to at least properly colored edges.
It is known that -partial -coloring (a.k.a. weak -coloring) is easy
for any . As our main result, we show that -partial -coloring
becomes hard as soon as , no matter how large a we have.
We also show that this is fundamentally different from -partial
-coloring: no matter which we choose, the problem is always hard
for but it becomes easy when . The same was known previously
for partial -coloring with , but the case of was open
Eviction of a 125 GeV "heavy"-Higgs from the MSSM
We prove that the present experimental constraints are already enough to rule
out the possibility of the ~125 GeV Higgs found at LHC being the second
lightest Higgs in a general MSSM context, even with explicit CP violation in
the Higgs potential. Contrary to previous studies, we are able to eliminate
this possibility analytically, using simple expressions for a relatively small
number of observables. We show that the present LHC constraints on the diphoton
signal strength, tau-tau production through Higgs and BR(B -> X_s gamma) are
enough to preclude the possibility of H_2 being the observed Higgs with m_H~125
GeV within an MSSM context, without leaving room for finely tuned
cancellations. As a by-product, we also comment on the difficulties of an MSSM
interpretation of the excess in the gamma-gamma production cross section
recently found at CMS that could correspond to a second Higgs resonance at
m_H~136 GeV.Comment: 38 pages, 9 figures. Final version accepted at JHEP. Sections 2, 3
and appendices simplified. Experimental results updated, several references
added. Small typos corrected and a new comparison of approximate formulas
with full expressions include
Neutrino Observatories Can Characterize Cosmic Sources and Neutrino Properties
Neutrino telescopes that measure relative fluxes of ultrahigh-energy
can give information about the location and
characteristics of sources, about neutrino mixing, and can test for neutrino
instability and for departures from CPT invariance in the neutrino sector. We
investigate consequences of neutrino mixing for the neutrino flux arriving at
Earth, and consider how terrestrial measurements can characterize distant
sources. We contrast mixtures that arise from neutrino oscillations with those
signaling neutrino decays. We stress the importance of measuring fluxes in neutrino observatories.Comment: 9 RevTeX pages, 4 figure
Baryogenesis from a right-handed neutrino condensate
We show that the baryon asymmetry of the Universe can be generated by a
strongly coupled right handed neutrino condensate which also drives inflation.
The resulting model has only a small number of parameters, which completely
determine not only the baryon asymmetry of the Universe and the mass of the
right handed neutrino but also the inflationary phase. This feature allows us
to make predictions that will be tested by current and planned experiments. As
compared to the usual approach our dynamical framework is both economical and
predictive.Comment: 13 pages, 3 figures. Typos corrected and several points clarified.
Results unchanged. New references adde
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.
CPT Violation and the Nature of Neutrinos
In order to accommodate the neutrino oscillation signals from the solar,
atmospheric, and LSND data, a sterile fourth neutrino is generally invoked,
though the fits to the data are becoming more and more constrained. However, it
has recently been shown that the data can be explained with only three
neutrinos, if one invokes CPT violation to allow different masses and mixing
angles for neutrinos and antineutrinos. We explore the nature of neutrinos in
such CPT-violating scenarios. Majorana neutrino masses are allowed, but in
general, there are no longer Majorana neutrinos in the conventional sense.
However, CPT-violating models still have interesting consequences for
neutrinoless double beta decay. Compared to the usual case, while the larger
mass scale (from LSND) may appear, a greater degree of suppression can also
occur.Comment: 10 pages, 1 figur
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