403 research outputs found
CP-violating Majorana phases, lepton-conserving processes and final state interactions
The CP-violating phases associated with Majorana neutrinos can give rise to
CP-violating effects even in processes that conserve total Lepton number, such
as \mu -> eee+, \mu + e -> e + e and others. After explaining the reasons that
make this happen, we consider the calculation of the rates for the process of
the form \ell_a + \ell_b -> \ell_a + \ell_c, and its conjugate \bar\ell_a +
\bar\ell_b -> \bar\ell_a + \bar\ell_c, where \ell_a, \ell_b and \ell_c denote
charged leptons of different flavors. In the context of the Standard Model with
Majorana neutrinos, we show that the difference in the rates depends on such
phases. Our calculations illustrate in detail the mechanics that operate behind
the scene, and set the stage for carrying out the analogous, more complicated
(as we explain), calculations for other processes such as \mu -> eee+ and its
conjugate.Comment: Latex, axodraw, 24 page
Fractional helicity, Lorentz symmetry breaking, compactification and anyons
We construct the covariant, spinor sets of relativistic wave equations for a
massless field on the basis of the two copies of the R-deformed Heisenberg
algebra. For the finite-dimensional representations of the algebra they give a
universal description of the states with integer and half-integer helicity. The
infinite-dimensional representations correspond formally to the massless states
with fractional (real) helicity. The solutions of the latter type, however,
break down the (3+1) Poincar\'e invariance to the (2+1) Poincar\'e
invariance, and via a compactification on a circle a consistent theory for
massive anyons in =2+1 is produced. A general analysis of the ``helicity
equation'' shows that the (3+1) Poincar\'e group has no massless irreducible
representations with the trivial non-compact part of the little group
constructed on the basis of the infinite-dimensional representations of
sl(2,\CC). This result is in contrast with the massive case where integer and
half-integer spin states can be described on the basis of such representations,
and means, in particular, that the (3+1) Dirac positive energy covariant
equations have no massless limit.Comment: 19 pages; minor changes, references added. To appear in Nucl. Phys.
Searching a bitstream in linear time for the longest substring of any given density
Given an arbitrary bitstream, we consider the problem of finding the longest
substring whose ratio of ones to zeroes equals a given value. The central
result of this paper is an algorithm that solves this problem in linear time.
The method involves (i) reformulating the problem as a constrained walk through
a sparse matrix, and then (ii) developing a data structure for this sparse
matrix that allows us to perform each step of the walk in amortised constant
time. We also give a linear time algorithm to find the longest substring whose
ratio of ones to zeroes is bounded below by a given value. Both problems have
practical relevance to cryptography and bioinformatics.Comment: 22 pages, 19 figures; v2: minor edits and enhancement
Lorentz-invariant CPT violation
A Lorentz-invariant CPT violation, which may be termed as long-distance CPT
violation in contrast to the familiar short-distance CPT violation, has been
recently proposed. This scheme is based on a non-local interaction vertex and
characterized by an infrared divergent form factor. We show that the Lorentz
covariant -product is consistently defined and the energy-momentum
conservation is preserved in perturbation theory if the path integral is
suitably defined for this non-local theory, although unitarity is generally
lost. It is illustrated that T violation is realized in the decay and formation
processes. It is also argued that the equality of masses and decay widths of
the particle and anti-particle is preserved if the non-local CPT violation is
incorporated either directly or as perturbation by starting with the
conventional CPT-even local Lagrangian. However, we also explicitly show that
the present non-local scheme can induce the splitting of particle and
anti-particle mass eigenvalues if one considers a more general class of
Lagrangians.Comment: 28 pages; note added in proof; version published in Eur. Phys. J. C
(2013) 73: 234
Blood-brain barrier leakage and microvascular lesions in cerebral amyloid angiopathy
Background and Purpose-Cerebral amyloid angiopathy (CAA) is a common small vessel disease that independently effects cognition in older individuals. The pathophysiology of CAA and CAA-related bleeding remains poorly understood. In this postmortem study, we explored whether blood-brain barrier leakage is associated with CAA and microvascular lesions.Methods-Eleven CAA cases (median [IQR] age=69 years [65-79 years], 8 males) and 7 cases without neurological disease or brain lesions (median [IQR] age=77 years [68-92 years], 4 males) were analyzed. Cortical sections were sampled from each lobe, and IgG and fibrin extravasation (markers of blood-brain barrier leakage) were assessed with immunohistochemistry. We hypothesized that IgG and fibrin extravasation would be increased in CAA cases compared with controls, that this would be more pronounced in parietooccipital brain regions compared with frontotemporal brain regions in parallel with the posterior predilection of CAA, and would be associated with CAA severity and number of cerebral microbleeds and cerebral microinfarcts counted on ex vivo magnetic resonance imaging of the intact brain hemisphere.Results-Our results demonstrated increased IgG positivity in the frontotemporal (P=0.044) and parietooccipital (P=0.001) cortex in CAA cases compared with controls. Within CAA cases, both fibrin and IgG positivity were increased in parietooccipital brain regions compared with frontotemporal brain regions (P=0.005 and P=0.006, respectively). The percentage of positive vessels for fibrin and IgG was associated with the percentage of amyloid-beta-positive vessels (Spearman.=0.71, P=0.015 and Spearman.=0.73, P=0.011, respectively). Moreover, the percentage of fibrin and IgGpositive vessels, but not amyloid-beta-positive vessels, was associated with the number of cerebral microbleeds on magnetic resonance imaging (Spearman.=0.77, P=0.005 and Spearman.=0.70, P=0.017, respectively). Finally, we observed fibrin deposition in walls of vessels involved in cerebral microbleeds.Conclusions-Our results raise the possibility that blood-brain barrier leakage may be a contributory mechanism for CAArelated brain injury
CP violation in a multi-Higgs doublet model with flavor changing neutral current
We study CP violation in a multi-Higgs doublet model based on a horizontal symmetry where CKM phase is not the principal source of CP
violation. We consider two mechanisms for CP violation in this model: a) CP
violation due to complex Yukawa couplings; and b) CP violation due to
scalar-pseudoscalar Higgs boson mixings. Both mechanisms can explain the
observed CP violation in the neutral Kaon system. due to
neutral Higgs boson exchange is small in both mechanisms, but charged Higgs
boson con- tributions can be as large as for a), and for
b). CP violation in the neutral B system is, however, quite different from the
Minimal Standard
Model. The neutron Electric Dipole Moment can be as large as the present ex-
perimental bound, and can be used to constrain charged Higgs boson masses.
The electron
EDM is one order of magnitude below the experimental bound in case b) and
smaller in case a).Comment: 22 pages, Revtex, OITS-52
Probing Lorentz and CPT violation with space-based experiments
Space-based experiments offer sensitivity to numerous unmeasured effects
involving Lorentz and CPT violation. We provide a classification of clock
sensitivities and present explicit expressions for time variations arising in
such experiments from nonzero coefficients in the Lorentz- and CPT-violating
Standard-Model Extension.Comment: 15 page
Threshold analyses and Lorentz violation
In the context of threshold investigations of Lorentz violation, we discuss
the fundamental principle of coordinate invariance, the role of an effective
dynamical framework, and the conditions of positivity and causality. Our
analysis excludes a variety of previously considered Lorentz-breaking
parameters and opens an avenue for viable dispersion-relation investigations of
Lorentz violation.Comment: 9 page
Universal Texture of Quark and Lepton Mass Matrices and a Discrete Symmetry Z_3
Recent neutrino data have been favourable to a nearly bimaximal mixing, which
suggests a simple form of the neutrino mass matrix. Stimulated by this matrix
form, a possibility that all the mass matrices of quarks and leptons have the
same form as in the neutrinos is investigated. The mass matrix form is
constrained by a discrete symmetry Z_3 and a permutation symmetry S_2. The
model, of course, leads to a nearly bimaximal mixing for the lepton sectors,
while, for the quark sectors, it can lead to reasonable values of the CKM
mixing matrix and masses.Comment: 24 pages, RevTEX, no figure, some references and comments were adde
Lorentz and CPT Violation in Neutrinos
A general formalism is presented for violations of Lorentz and CPT symmetry
in the neutrino sector. The effective hamiltonian for neutrino propagation in
the presence of Lorentz and CPT violation is derived, and its properties are
studied. Possible definitive signals in existing and future
neutrino-oscillation experiments are discussed. Among the predictions are
direction-dependent effects, including neutrino-antineutrino mixing, sidereal
and annual variations, and compass asymmetries. Other consequences of Lorentz
and CPT violation involve unconventional energy dependences in oscillation
lengths and mixing angles. A variety of simple models both with and without
neutrino masses are developed to illustrate key physical effects. The
attainable sensitivities to coefficients for Lorentz violation in the
Standard-Model Extension are estimated for various types of experiments. Many
experiments have potential sensitivity to Planck-suppressed effects, comparable
to the best tests in other sectors. The lack of existing experimental
constraints, the wide range of available coefficient space, and the variety of
novel effects imply that some or perhaps even all of the existing data on
neutrino oscillations might be due to Lorentz and CPT violation.Comment: 25 pages REVTe
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