1,288 research outputs found
Vortices, zero modes and fractionalization in bilayer-graphene exciton condensate
A real-space formulation is given for the recently discussed exciton
condensate in a symmetrically biased graphene bilayer. We show that in the
continuum limit an oddly-quantized vortex in this condensate binds exactly one
zero mode per valley index of the bilayer. In the full lattice model the zero
modes are split slightly due to intervalley mixing. We support these results by
an exact numerical diagonalization of the lattice Hamiltonian. We also discuss
the effect of the zero modes on the charge content of these vortices and deduce
some of their interesting properties.Comment: (v2) A typo in Fig. 1 and a slight error in Eq. (4) corrected; all
the main results and conclusions remain unchange
Some Calculable Contributions to Entanglement Entropy
Entanglement entropy appears as a central property of quantum systems in
broad areas of physics. However, its precise value is often sensitive to
unknown microphysics, rendering it incalculable. By considering parametric
dependence on correlation length, we extract finite, calculable contributions
to the entanglement entropy for a scalar field between the interior and
exterior of a spatial domain of arbitrary shape. The leading term is
proportional to the area of the dividing boundary; we also extract finite
subleading contributions for a field defined in the bulk interior of a
waveguide in 3+1 dimensions, including terms proportional to the waveguide's
cross-sectional geometry; its area, perimeter length, and integrated curvature.
We also consider related quantities at criticality and suggest a class of
systems for which these contributions might be measurable.Comment: 4+ pages, 1 figure. v2: Some clarifications and more references;
updated to resemble version published in PR
Confinement and the quark Fermi-surface in SU(2N) QCD-like theories
Yang-Mills theories with a gauge group SU(N_c\=3)and quark matter in the
fundamental representation share many properties with the theory of strong
interactions, QCD with N_c=3. We show that, for N_c even and in the confinement
phase, the gluonic average of the quark determinant is independent of the
boundary conditions, periodic or anti-periodic ones. We then argue that a Fermi
sphere of quarks can only exist under extreme conditions when the centre
symmetry is spontaneously broken and colour is liberated. Our findings are
supported by lattice gauge simulations for N_c=2...5 and are illustrated by
means of a simple quark model.Comment: 5 pages, 2 figures, revised journal versio
Scaling of the superconducting transition temperature in underdoped high-Tc cuprates with a pseudogap energy: Does this support the anyon model of their superfluidity?
In earlier work, we have been concerned with the scaling properties of some
classes of superconductors, specifically with heavy Fermion materials and with
five bcc transition metals of BCS character. Both of these classes of
superconductors were three-dimensional but here we are concerned solely with
quasi-two-dimensional high-Tc cuprates in the underdoped region of their phase
diagram. A characteristic feature of this part of the phase diagram is the
existence of a pseudogap (pg). We therefore build our approach around the
assumption that kB Tc / E_pg is the basic dimensionless ratio on which to
focus, where the energy E_pg introduced above is a measure of the pseudogap.
Since anyon fractional statistics apply to two-dimensional assemblies, we
expect the fractional statistics parameter allowing `interpolation' between
Fermi-Dirac and Bose-Einstein statistical distribution functions as limiting
cases to play a significant role in determining kB Tc / E_pg and experimental
data are analyzed with this in mind.Comment: Phys. Chem. Liquids, to be publishe
Asymptotic Freedom: From Paradox to Paradigm
Asymptotic freedom was developed as a response to two paradoxes: the
weirdness of quarks, and in particular their failure to radiate copiously when
struck; and the coexistence of special relativity and quantum theory, despite
the apparent singularity of quantum field theory. It resolved these paradoxes,
and catalyzed the development of several modern paradigms: the hard reality of
quarks and gluons, the origin of mass from energy, the simplicity of the early
universe, and the power of symmetry as a guide to physical law.Comment: 26 pages, 10 figures. Lecture on receipt of the 2004 Nobel Prize. v2:
typo (in Ohm's law) correcte
Generalized Aharonov-Bohm effect, homotopy classes and Hausdorff dimension
We suggest as gedanken experiment a generalization of the Aharonov-Bohm
experiment, based on an array of solenoids. This experiment allows in principle
to measure the decomposition into homotopy classes of the quantum mechanical
propagator. This yields information on the geometry of the average path of
propagation and allows to determine its Hausdorff dimension.Comment: 14 pages, LaTeX + 3 figures, P
Quantum Numbers of Textured Hall Effect Quasiparticles
We propose a class of variational wave functions with slow variation in spin
and charge density and simple vortex structure at infinity, which properly
generalize both the Laughlin quasiparticles and baby Skyrmions. We argue that
the spin of the corresponding quasiparticle has a fractional part related in a
universal fashion to the properties of the bulk state, and propose a direct
experimental test of this claim. We show that certain spin-singlet quantum Hall
states can be understood as arising from primary polarized states by Skyrmion
condensation.Comment: 13 pages, no figures, Phyzz
Quark Mass Textures and sin 2 beta
Recent precise measurements of sin 2 beta from the B-factories (BABAR and
BELLE) and a better known strange quark mass from lattice QCD make precision
tests of predictive texture models possible. The models tested include those
hierarchical N-zero textures classified by Ramond, Roberts and Ross, as well as
any other hierarchical matrix Ansatz with non-zero 12 = 21 and vanishing 11 and
13 elements. We calculate the maximally allowed value for sin 2 beta in these
models and show that all the aforementioned models with vanishing 11 and 13
elements are ruled out at the 3 sigma level. While at present sin 2 beta and
|Vub/Vcb| are equally good for testing N-zero texture models, in the near
future the former will surpass the latter in constraining power.Comment: 1+20 pages, 2 figures, JHEP3 clas
The strong-CP question in SU(3)_c X SU(3)_L X U(1)_N models
We analyze two recent models based on the gauge group
SU(3)SU(3)U(1) where each generation is not
anomaly-free, but anomaly cancels when three generations are taken into
account. We show that the most general Yukawa couplings of these models admit
of a Peccei-Quinn symmetry. This symmetry can be extended to the entire
Lagrangian by using extra fields in a very elegant way so that the resulting
axion can be made invisible.Comment: Latex, 8 pages, no figure
Systematic Study Of Leptonic Mixing In A Class Of SU_H(2) Models
We perform a systematic analysis of the PMNS matrices which arise when one
assigns the three generations of leptons to the representation of a
horizontal symmetry. This idea has been previously explored by
Kuchimanchi and Mohapatra. However, we assume the neutrino mass matrix
results from leptonic couplings to triplet scalar fields and
hierarchies exist amongst lepton mass matrix elements which result from
couplings to scalar fields with different charges. Of the sixteen
candidate PMNS matrices which result it is found that only one is both
predictive and possesses a leading order structure compatible with experimental
data. The relevant neutrino mass matrix displays the symmetry
to leading order and we explore the perturbations required
to produce a realistic lepton spectrum. The effective mass in neutrinoless
double beta decay is required to lie in the range
, which is just below current
experimental bounds. is non-zero but not uniquely determined.Comment: To appear in Phys. Rev.
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