2,640 research outputs found
A direct road to Majorana fields
A concise discussion of spin-1/2 field equations with a special focus on
Majorana spinors is presented. The Majorana formalism which describes massive
neutral fermions by the help of two-component or four-component spinors is of
fundamental importance for the understanding of mathematical aspects of
supersymmetric and other extensions of the Standard Model of particle physics,
which may play an increasingly important role at the beginning of the LHC era.
The interplay between the two-component and the four-component formalism is
highlighted in an introductory way. Majorana particles are predicted both by
grand unified theories, in which these particles are neutrinos, and by
supersymmetric theories, in which they are photinos, gluinos and other states.Comment: 30 pages, LATEX, one section expanded and references adde
Proximity-induced supercurrent through topological insulator based nanowires for quantum computation studies
Proximity induced superconducting energy gap in the surface states of
topological insulators has been predicted to host the much wanted Majorana
fermions for fault tolerant quantum computation. Recent theoretically proposed
architectures for topological quantum computation via Majoranas are based on
large networks of Kitaevs one dimensional quantum wires, which pose a huge
experimental challenge in terms of scalability of the current single nanowire
based devices. Here, we address this problem by realizing robust
superconductivity in junctions of fabricated topological insulator Bi2Se3
nanowires proximity coupled to conventional s wave superconducting W
electrodes. Milling technique possesses great potential in fabrication of any
desired shapes and structures at nanoscale level, and therefore can be
effectively utilized to scale up the existing single nanowire based design into
nanowire based network architectures. We demonstrate the dominant role of
ballistic topological surface states in propagating the long range proximity
induced superconducting order with high IcRN product in long Bi2Se3 junctions.
Large upper critical magnetic fields exceeding the Chandrasekhar Clogston limit
suggests the existence of robust superconducting order with spin triplet cooper
pairing. An unconventional inverse dependence of IcRN product on the width of
the nanowire junction was also observed.Comment: 12 page
Superconductivity in a spin liquid - a one dimensional example
We study a one-dimensional model of interacting conduction electrons with a
two-fold degenerate band away from half filling. The interaction includes an
on-site Coulomb repulsion and Hund's rule coupling. We show that such
one-dimensional system has a divergent Cooper pair susceptibility at T = 0,
provided the Coulomb interaction between electrons on the same orbital and
the modulus of the Hund's exchange integral are larger than the
interorbital Coulomb interaction. It is remarkable that the superconductivity
can be achieved for {\it any} sign of . The opening of spectral gaps makes
this state stable with respect to direct electron hopping between the orbitals.
The scaling dimension of the superconducting order parameter is found to be
between 1/4 (small ) and 1/2 (large ).Comment: 11 pages, Latex, no figure
A locally supersymmetric invariant action for supergravity
We present an action for supergravity in dimensions, containing
the gauge fields of the superalgebra, i.e. one-forms with
=1,2,5,6,9,10 antisymmetric D=12 Lorentz indices and a Majorana gravitino
. The vielbein and spin connection correspond to and
respectively. The action is not gauge invariant under the full
superalgebra, but only under a subalgebra (containing the
algebra ), whose gauge fields are , ,
and the Weyl projected Majorana gravitino .
Supersymmetry transformations are therefore generated by a Majorana-Weyl
supercharge and, being part of a gauge superalgebra, close off-shell. The
action is simply where is the
curvature supermatrix two-form, and is a constant
supermatrix involving and breaking to its subalgebra. The action includes the usual Einstein-Hilbert term.Comment: LaTeX, 13 pages. Added a reference, a Table in Appendix A for the
gamma commutations in d=12, and corrected eq. (4.14) for the Einstein-Hilbert
term; v4: corrected formulas (A.3), (A.4) and (A.10), modified last paragraph
of Section 5, added acknowledgement
Neutrinos and the matter-antimatter asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero
neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny
constitutes a puzzling problem in particle physics. From the theoretical
viewpoint, the smallness of neutrino masses can be elegantly explained through
the seesaw mechanism. Another challenging issue for particle physics and
cosmology is the explanation of the matter-antimatter asymmetry observed in
Nature. Among the viable mechanisms, leptogenesis is a simple and
well-motivated framework. In this talk we briefly review these aspects, making
emphasis on the possibility of linking neutrino physics to the cosmological
baryon asymmetry originated from leptogenesis.Comment: 8 pages, 1 table, 1 figure; Based on talk given at the Symposium
STARS2011, 1 - 4 May 2011, Havana, Cuba; to be published in the Proceeding
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