5,717 research outputs found
Pole expansion of self-energy and interaction effect on topological insulators
We study effect of interactions on time-reversal-invariant topological
insulators. Their topological indices are expressed by interacting Green's
functions. Under the local self-energy approximation, we connect topological
index and surface states of an interacting system to an auxiliary
noninteracting system, whose Hamiltonian is related to the pole-expansions of
the local self-energy. This finding greatly simplifies the calculation of
interacting topological indices and gives an noninteracting pictorial
description of interaction driven topological phase transitions. Our results
also bridge studies of the correlated topological insulating materials with the
practical dynamical-mean-field-theory calculations.Comment: 4.2 pages, 3 figures, reference added, typos correcte
Simplified TeV leptophilic dark matter in light of DAMPE data
Using a simplified framework, we attempt to explain the recent DAMPE cosmic
flux excess by leptophilic Dirac fermion dark matter (LDM). The
scalar () and vector () mediator fields connecting LDM and
Standard Model particles are discussed. Under constraints of DM relic density,
gamma-rays, cosmic-rays and Cosmic Microwave Background (CMB), we find that the
couplings , , and can
produce the right bump in flux for a DM mass around 1.5 TeV with a
natural thermal annihilation cross-section today. Among them, coupling is tightly constrained by
PandaX-II data (although LDM-nucleus scattering appears at one-loop level) and
the surviving samples appear in the resonant region, . We also study the related collider signatures, such as dilepton
production , and muon anomaly. Finally,
we present a possible realization for such leptophilic dark matter.Comment: discussions added, version accepted by JHE
Split orthogonal group: A guiding principle for sign-problem-free fermionic simulations
We present a guiding principle for designing fermionic Hamiltonians and
quantum Monte Carlo (QMC) methods that are free from the infamous sign problem
by exploiting the Lie groups and Lie algebras that appear naturally in the
Monte Carlo weight of fermionic QMC simulations. Specifically, rigorous
mathematical constraints on the determinants involving matrices that lie in the
split orthogonal group provide a guideline for sign-free simulations of
fermionic models on bipartite lattices. This guiding principle not only unifies
the recent solutions of the sign problem based on the continuous-time quantum
Monte Carlo methods and the Majorana representation, but also suggests new
efficient algorithms to simulate physical systems that were previously
prohibitive because of the sign problem.Comment: See
http://mathoverflow.net/questions/204460/how-to-prove-this-determinant-is-positive
and
https://terrytao.wordpress.com/2015/05/03/the-standard-branch-of-the-matrix-logarithm/
for discussions on mathematical aspect of the paper; v3 added footnotes [44,
59] and new supplemental materia
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