1,096 research outputs found
Spectral properties of truncated Toeplitz operators by equivalence after extension
We study truncated Toeplitz operators in model spaces View the MathML source for 1<p<∞, with essentially bounded symbols in a class including the algebra View the MathML source, as well as sums of analytic and anti-analytic functions satisfying a θ -separation condition, using their equivalence after extension to Toeplitz operators with 2×2 matrix symbols. We establish Fredholmness and invertibility criteria for truncated Toeplitz operators with θ -separated symbols and, in particular, we identify a class of operators for which semi-Fredholmness is equivalent to invertibility. For symbols in View the MathML source, we extend to all p∈(1,∞) the spectral mapping theorem for the essential spectrum. Stronger results are obtained in the case of operators with rational symbols, or if the underlying model space is finite-dimensional
Paired kernels and their applications
This paper considers paired operators in the context of the Lebesgue Hilbert
space on the unit circle and its subspace, the Hardy space . The kernels
of such operators, together with their analytic projections, which are
generalizations of Toeplitz kernels, are studied. Results on near-invariance
properties, representations, and inclusion relations for these kernels are
obtained. The existence of a minimal Toeplitz kernel containing any projected
paired kernel and, more generally, any nearly -invariant subspace of
, is derived. The results are applied to describing the kernels of
finite-rank asymmetric truncated Toeplitz operators.Comment: 26 page
Model spaces and Toeplitz kernels in reflexive Hardy spaces
This paper considers model spaces in an Hp setting. The existence of unbounded
functions and the characterisation of maximal functions in a model space are studied, and decomposition
results for Toeplitz kernels, in terms of model spaces, are establishedFCT/Portuga
Dark linear seesaw mechanism
We propose a minimal model where a dark sector, odd under a
discrete symmetry, is the seed of lepton number violation in the neutrino
sector at the loop level, in the context of the linear seesaw mechanism.
Neutrino mass suppression stems from a naturally small scalar potential
coupling which breaks the lepton number symmetry softly. The fact that we
consider (dark) Dirac vector-like neutral leptons, prevents the appearance of
other mass terms that could contribute to neutrino masses via alternative
mechanisms. We study the dark-matter phenomenology of the model, focusing on
the case in which the stable particle is the lightest neutral scalar arising
from the dark scalar sector. Prospects for testing our framework with the
results of current and future lepton flavour violation searches are also
discussed.Comment: 13 LaTeX pages, 3 figure
Kernels of unbounded Toeplitz operators and factorization of symbols
We consider kernels of unbounded Toeplitz operators in Hp(C+) in terms of a factorization of their symbols. We study the existence of a minimal Toeplitz kernel containing a given function in Hp(C+), we describe the kernels of Toeplitz operators whose symbol possesses a certain factorization involving two different Hardy spaces and we establish relations between the kernels of two operators whose symbols differ by a factor which corresponds, in the unit circle, to a non-integer power of z. We apply the results to describe the kernels of Toeplitz operators with non-vanishing piecewise continuous symbols.This work was partially supported by FCT/Portugal through UID/MAT/04459/2020. The research of M. T. Malheiro was partially supported by Portuguese Funds through FCT/Portugal within the Projects UIDB/00013/2020 and UIDP/00013/2020
Hybrid scoto/seesaw: flavour and dark matter
We propose a model based on the interplay between the type-II seesaw and
scotogenic neutrino mass generation mechanisms. The setup features a
discrete flavour symmetry which is broken down to a residual
responsible for stabilising dark matter. A singlet scalar field
is introduced to implement spontaneous CP violation. The effective neutrino
mass matrix two-texture zero structure leads to sharp neutrino sector
predictions. We analyse the constraints imposed on the model by current and
future charged lepton flavour violation experiments. This framework provides
two viable dark matter candidates, scalar or fermion. We investigate the scalar
dark matter scenario considering relic density, direct-detection and collider
constraints.Comment: 8 LaTeX pages; 4 figures. Contribution to the Proceedings of the 8th
Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2022),
7-11 November 2022, Baden-Baden, German
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