146,154 research outputs found
A symmetry for vanishing cosmological constant: Another realization
A more conventional realization of a symmetry which had been proposed towards
the solution of cosmological constant problem is considered. In this study the
multiplication of the coordinates by the imaginary number in the literature
is replaced by the multiplication of the metric tensor by minus one. This
realization of the symmetry as well forbids a bulk cosmological constant and
selects out dimensional spaces. On contrary to its previous
realization the symmetry, without any need for its extension, also forbids a
possible cosmological constant term which may arise from the extra dimensional
curvature scalar provided that the space is taken as the union of two
dimensional spaces where the usual 4-dimensional space lies at the intersection
of these spaces. It is shown that this symmetry may be realized through
spacetime reflections that change the sign of the volume element. A possible
relation of this symmetry to the E-parity symmetry of Linde is also pointed
out.Comment: The version to appear in PLB. The terms "non-orientable space" and
"extra-dimensional tranlation" are replaced by "space whose volume element
changes sign under extra dimensional reflections" and "extra dimensional
reflections", respectively; and typos are correcte
The construction of generalized Dirac operators on the lattice
We discuss the steps to construct Dirac operators which have arbitrary
fermion offsets, gauge paths, a general structure in Dirac space and satisfy
the basic symmetries (gauge symmetry, hermiticity condition, charge
conjugation, hypercubic rotations and reflections) on the lattice. We give an
extensive set of examples and offer help to add further structures.Comment: 19 pages, latex, maple code attache
Topological phases protected by point group symmetry
We consider symmetry protected topological (SPT) phases with crystalline
point group symmetry, dubbed point group SPT (pgSPT) phases. We show that such
phases can be understood in terms of lower-dimensional topological phases with
on-site symmetry, and can be constructed as stacks and arrays of these
lower-dimensional states. This provides the basis for a general framework to
classify and characterize bosonic and fermionic pgSPT phases, that can be
applied for arbitrary crystalline point group symmetry and in arbitrary spatial
dimension. We develop and illustrate this framework by means of a few examples,
focusing on three-dimensional states. We classify bosonic pgSPT phases and
fermionic topological crystalline superconductors with (reflection)
symmetry, electronic topological crystalline insulators (TCIs) with symmetry, and bosonic pgSPT phases with symmetry,
which is generated by two perpendicular mirror reflections. We also study
surface properties, with a focus on gapped, topologically ordered surface
states. For electronic TCIs we find a classification, where
the corresponds to known states obtained from non-interacting electrons,
and the corresponds to a "strongly correlated" TCI that requires strong
interactions in the bulk. Our approach may also point the way toward a general
theory of symmetry enriched topological (SET) phases with crystalline point
group symmetry.Comment: v2: Minor changes/additions to introduction and discussion sections,
references added, published version. 21 pages, 11 figure
Momentum distribution dynamics of a Tonks-Girardeau gas: Bragg reflections of a quantum many-body wavepacket
The dynamics of the momentum distribution and the reduced single-particle
density matrix (RSPDM) of a Tonks-Girardeau (TG) gas is studied in the context
of Bragg-reflections of a many-body wavepacket. We find strong suppression of a
Bragg-reflection peak for a dense TG wavepacket; our observation illustrates
dependence of the momentum distribution on the interactions/wavefunction
symmetry. The momentum distribution is calculated with a fast algorithm based
on a formula expressing the RSPDM via a dynamically evolving single-particle
basis
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