145,523 research outputs found
Multiple Chirality in Nuclear Rotation: A Microscopic View
Covariant density functional theory and three-dimensional tilted axis
cranking are used to investigate multiple chirality in nuclear rotation for the
first time in a fully self-consistent and microscopic way. Two distinct sets of
chiral solutions with negative and positive parities, respectively, are found
in the nucleus 106Rh. The negative-parity solutions reproduce well the
corresponding experimental spectrum as well as the B(M1)/B(E2) ratios of the
transition strengths. This indicates that a predicted positive-parity chiral
band should also exist. Therefore, it provides a further strong hint that
multiple chirality is realized in nuclei.Comment: 15 pages, 5 figures, 1 tabl
Narrative in design development
This paper describes the value of narrative used with ideation tools in aiding the rapid production of product concepts and designs for masters students of graphics, fine art, product and industrial design. The ideation tools used alongside narrative included elements of divergent and convergent thinking in combination with reverse engineering and functional analysis, and practical prototyping using a range of readily adapted artefacts. Narrative was introduced and used by the students in order to ensure the development of a context and purpose for the product, artefact or system developed or proposed and to stimulate original product concepts, ideas and thinking. The concept of narrative is familiar in design. Here however the concept was reinforced using structures associated with fictional narrative. Reverse engineering exploring the deconstruction and identification of function for each component in a product was used to aid students ensure practicality in their idea implementation. This paper describes positive experiences resulting from this activity, with a particular focus on the value of narrative in developing robust concepts. The use of physical prototyping provided tangible and instant feedback for divergent and convergent phases of idea development
Complete time-dependent treatment of a three-level system
Both unitary evolution and the effects of dissipation and decoherence for a
general three-level system are of widespread interest in quantum optics,
molecular physics, and elsewhere. A previous paper presented a technique for
solving the time-dependent operator equations involved but under certain
restrictive conditions. We now extend our results to a general three-level
system with arbitrary time-dependent Hamiltonians and Lindblad operators.
Analytical handling of the SU(3) algebra of the eight operators involved leaves
behind a set of coupled first-order differential equations for classical
functions. Solution of this set gives a complete solution of the quantum
problem, without having to invoke rotating-wave or other approximations.
Numerical illustrations are given.Comment: 1 tar.gz file containing a Tex and four eps figure files; unzip with
command gunzip RZPRA05.tar.g
Nonsymmorphic symmetry-required band crossings in topological semimetals
We show that for two-band systems nonsymmorphic symmetries may enforce the
existence of band crossings in the bulk, which realize Fermi surfaces of
reduced dimensionality. We find that these unavoidable crossings originate from
the momentum dependence of the nonsymmorphic symmetry, which puts strong
restrictions on the global structure of the band configurations. Three
different types of nonsymmorphic symmetries are considered: (i) a unitary
nonsymmorphic symmetry, (ii) a nonsymmorphic magnetic symmetry, and (iii) a
nonsymmorphic symmetry combined with inversion. For nonsymmorphic symmetries of
the latter two types, the band crossings are located at high-symmetry points of
the Brillouin zone, with their exact positions being determined by the algebra
of the symmetry operators. To characterize these band degeneracies we introduce
a \emph{global} topological charge and show that it is of type,
which is in contrast to the \emph{local} topological charge of Fermi points in,
say, Weyl semimetals. To illustrate these concepts, we discuss the -flux
state as well as the SSH model at its critical point and show that these two
models fit nicely into our general framework of nonsymmorphic two-band systems.Comment: 6.5 pages, 4 figure
Triplet-Quadruplet Dark Matter
We explore a dark matter model extending the standard model particle content
by one fermionic triplet and two fermionic quadruplets,
leading to a minimal realistic UV-complete model of electroweakly interacting
dark matter which interacts with the Higgs doublet at tree level via two kinds
of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum
of the dark sector consists of three Majorana fermions, three singly charged
fermions, and one doubly charged fermion, with the lightest neutral fermion
serving as a dark matter candidate. A typical spectrum exhibits a
large degree of degeneracy in mass between the neutral and charged fermions,
and we examine the one-loop corrections to the mass differences to ensure that
the lightest particle is neutral. We identify regions of parameter space for
which the dark matter abundance is saturated for a standard cosmology,
including coannihilation channels, and find that this is typically achieved for
. Constraints from precision electroweak
measurements, searches for dark matter scattering with nuclei, and dark matter
annihilation are important, but leave open a viable range for a thermal relic.Comment: 27 pages, 6 figures. v2: minor revisions to match published versio
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