4,027 research outputs found
Generalized Ehrhart polynomials
Let be a polytope with rational vertices. A classical theorem of Ehrhart
states that the number of lattice points in the dilations is a
quasi-polynomial in . We generalize this theorem by allowing the vertices of
P(n) to be arbitrary rational functions in . In this case we prove that the
number of lattice points in P(n) is a quasi-polynomial for sufficiently
large. Our work was motivated by a conjecture of Ehrhart on the number of
solutions to parametrized linear Diophantine equations whose coefficients are
polynomials in , and we explain how these two problems are related.Comment: 18 pages, no figures; v2: Sections 4 and 5 added, proofs and
exposition have been expanded and clarifie
Magnetoresistance from Fermi Surface Topology
Extremely large non-saturating magnetoresistance has recently been reported
for a large number of both topologically trivial and non-trivial materials.
Different mechanisms have been proposed to explain the observed
magnetotransport properties, yet without arriving to definitive conclusions or
portraying a global picture. In this work, we investigate the transverse
magnetoresistance of materials by combining the Fermi surfaces calculated from
first principles with the Boltzmann transport theory approach relying on the
semiclassical model and the relaxation time approximation. We first consider a
series of simple model Fermi surfaces to provide a didactic introduction into
the charge-carrier compensation and open-orbit mechanisms leading to
non-saturating magnetoresistance. We then address in detail magnetotransport in
three representative materials: (i) copper, a prototypical nearly free-electron
metal characterized by the open Fermi surface that results in an intricate
angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in
which very large magnetoresistance is known to result from charge-carrier
compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II
Weyl semimetal that holds the record of magnetoresistance in compounds. In all
three cases our calculations show excellent agreement with both the field
dependence of magnetoresistance and its anisotropy measured at low
temperatures. Furthermore, the calculations allow for a full interpretation of
the observed features in terms of the Fermi surface topology. These results
will help addressing a number of outstanding questions, such as the role of the
topological phase in the pronounced large non-saturating magnetoresistance
observed in topological materials.Comment: 13 pages, 9 figure
violation in charmed hadron decays into neutral kaons
We find a new violating effect in charmed hadron decays into neutral
kaons, which is induced by the interference between the Cabibbo-favored and
doubly Cabibbo-suppressed amplitudes with the mixing.
It is estimated to be of order of , much larger than the
direct asymmetry, but missed in the literature. To reveal this new
violation effect, we propose a new observable, the difference of the
asymmetries in the and
modes. Once the new effect is determined by experiments, the direct
asymmetry then can be extracted and used to search for new physics.Comment: 6 pages, 3 figures. Contribution to the proceeding of The 15th
International Conference on Flavor Physics & CP Violation, 5-9 June 2017,
Prague, Czech Republi
- …