5,108 research outputs found
Quantum Hall Effect in Thin Films of Three-Dimensional Topological Insulators
We show that a thin film of a three-dimensional topological insulator (3DTI)
with an exchange field is a realization of the famous Haldane model for quantum
Hall effect (QHE) without Landau levels. The exchange field plays the role of
staggered fluxes on the honeycomb lattice, and the hybridization gap of the
surface states is equivalent to alternating on-site energies on the AB
sublattices. A peculiar phase diagram for the QHE is predicted in 3DTI thin
films under an applied magnetic field, which is quite different from that
either in traditional QHE systems or in graphene.Comment: 4 pages, 4 figure
A topological look at the quantum spin Hall state
We propose a topological understanding of the quantum spin Hall state without
considering any symmetries, and it follows from the gauge invariance that
either the energy gap or the spin spectrum gap needs to close on the system
edges, the former scenario generally resulting in counterpropagating gapless
edge states. Based upon the Kane-Mele model with a uniform exchange field and a
sublattice staggered confining potential near the sample boundaries, we
demonstrate the existence of such gapless edge states and their robust
properties in the presence of impurities. These gapless edge states are
protected by the band topology alone, rather than any symmetries.Comment: 5 pages, 4 figure
Weak Decays of Stable Open-bottom Tetraquark by SU(3) Symmetry Analysis
The exotic state which was observed by D0 Collaboration is very
likely to be a tetraquark state with four different valence quark flavors,
though the existence was not confirmed by other collaborations. The possibility
of such state still generate lots of interests in theory. In the paper, we will
study the properties of the state under the SU(3) flavor symmetry. This four
quark state with a heavy bottom quark and three light quarks(anti-quark) can
form a or representation. The weak decays can be dominant
and should be discussed carefully while such state is stable against the strong
interaction. Therefor we will study the multi-body semileptonic and nonleptonic
weak decays systematically. With the help of SU(3) flavor symmetry, we can give
the Hamiltonian in the hadronic level, then obtain the parameterized
irreducible amplitudes and the relations of different channels. At the end of
the article, we collect some Cabibbo allowed two-body and three-body weak decay
channels which can be used to reconstruct states at the branching
fraction up to be .Comment: 53 pages, 2 figure
Top-Quark Decay at Next-to-Next-to-Leading Order in QCD
We present the complete calculation of the top-quark decay width at
next-to-next-to-leading order in QCD, including next-to-leading electroweak
corrections as well as finite bottom quark mass and boson width effects. In
particular, we also show the first results of the fully differential decay
rates for top-quark semileptonic decay at
next-to-next-to-leading order in QCD. Our method is based on the understanding
of the invariant mass distribution of the final-state jet in the singular limit
from effective field theory. Our result can be used to study arbitrary
infrared-safe observables of top-quark decay with the highest perturbative
accuracy.Comment: 5 pages, 6 figures; version accepted for publication in Physical
Review Letter
Weak Decays of Doubly Heavy Baryons: the case
Very recently, the LHCb collaboration has observed in the final state
a resonant structure that is identified as the
doubly-charmed baryon . Inspired by this observation, we
investigate the weak decays of doubly heavy baryons ,
, , ,
, , ,
and and focus on the decays into spin
baryons in this paper. At the quark level these decay processes are induced by
the or transitions, and the two spectator quarks can be
viewed as a scalar or axial vector diquark. We first derive the hadronic form
factors for these transitions in the light-front approach and then apply them
to predict the partial widths for the semi-leptonic and non-leptonic decays of
doubly heavy baryons. We find that a number of decay channels are sizable and
can be examined in future measurements at experimental facilities like LHC,
Belle II and CEPC.Comment: 40 pages, 4 figures, to appear in EPJ
Resummation prediction on top quark transverse momentum distribution at large pT
We study the factorization and resummation of t-channel top quark transverse
momentum distribution at large pT in the SM at both the Tevatron and the LHC
with soft-collinear effective theory. The cross section in the threshold region
can be factorized into a convolution of hard, jet and soft functions. In
particular, we first calculate the NLO soft functions for this process, and
give a RG improved cross section by evolving the different functions to a
common scale. Our results show that the resummation effects increase the NLO
results by about 9%-13% and 4%-9% when the top quark pT is larger than 50 and
70 GeV at the Tevatron and the 8 TeV LHC, respectively. Also, we discuss the
scale independence of the cross section analytically, and show how to choose
the proper scales at which the perturbative expansion can converge fast.Comment: 32 pages, 10 figures, version published in Phys.Rev.
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