48,279 research outputs found
N=2 higher-derivative couplings from strings
We consider the Calabi-Yau reduction of the Type IIA eight derivative
one-loop stringy corrections focusing on the couplings of the four dimensional
gravity multiplet with vector multiplets and a tensor multiplet containing the
NS two-form. We obtain a variety of higher derivative invariants generalising
the one-loop topological string coupling, , controlled by the lowest order
Kahler potential and two new non-topological quantities built out of the
Calabi-Yau Riemann curvature.Comment: 43 page
Topological Order and Quantum Criticality
In this chapter we discuss aspects of the quantum critical behavior that
occurs at a quantum phase transition separating a topological phase from a
conventionally ordered one. We concentrate on a family of quantum lattice
models, namely certain deformations of the toric code model, that exhibit
continuous quantum phase transitions. One such deformation leads to a
Lorentz-invariant transition in the 3D Ising universality class. An alternative
deformation gives rise to a so-called conformal quantum critical point where
equal-time correlations become conformally invariant and can be related to
those of the 2D Ising model. We study the behavior of several physical
observables, such as non-local operators and entanglement entropies, that can
be used to characterize these quantum phase transitions. Finally, we briefly
consider the role of thermal fluctuations and related phase transitions, before
closing with a short overview of field theoretical descriptions of these
quantum critical points.Comment: 24 pages, 7 figures, chapter of the book "Understanding Quantum Phase
Transitions", edited by Lincoln D. Carr (CRC Press / Taylor and Francis,
2010); v2: updated reference
The Ten-dimensional Effective Action of Strongly Coupled Heterotic String Theory
We derive the ten-dimensional effective action of the strongly coupled
heterotic string as the low energy limit of M-theory on S^1/Z_2. In contrast to
a conventional dimensional reduction, it is necessary to integrate out
nontrivial heavy modes which arise from the sources located on the orbifold
fixed hyperplanes. This procedure, characteristic of theories with dynamical
boundaries, is illustrated by a simple example. Using this method, we determine
a complete set of R^4, F^2R^2, and F^4 terms and the corresponding Chern-Simons
and Green-Schwarz terms in ten dimensions. As required by anomaly cancelation
and supersymmetry, these terms are found to exactly coincide with their weakly
coupled one-loop counterparts.Comment: 18 pages, Latex2e with amsmath, corrected some typo
Lepton-number violation and right-handed neutrinos in Higgs-less effective theories
Following previous work, we identify a symmetry S_nat that generalizes the
concept of custodial symmetry, keeping under control deviations from the
Standard Model (SM). To realize S_nat linearly, the space of gauge fields has
to be extended. Covariant constraints formulated in terms of spurions reduce
S_nat back to SU(2)_L x U(1)_Y. This allows for a covariant introduction of
explicit S_nat-breaking parameters. We assume that S_nat is at play in a theory
of electroweak symmetry-breaking without a light Higgs particle. We describe
some consequences of this assumption, using a non-decoupling effective theory
in which the loop expansion procedure is based on both momentum and spurion
power counting, as in Chiral Perturbation Theory. A hierarchy of lepton-number
violating effects follows. Leading corrections to the SM are non-oblique. The
effective theory includes stable light right-handed neutrinos, with an unbroken
Z_2 symmetry forbidding neutrino Dirac masses. nu_R contribution to dark matter
places bounds on their masses.Comment: Corresponds to published version: added subsection VI-D about
order-of-magnitude estimate
Mass-Gaps and Spin Chains for (Super) Membranes
We present a method for computing the non-perturbative mass-gap in the theory
of Bosonic membranes in flat background spacetimes with or without background
fluxes. The computation of mass-gaps is carried out using a matrix
regularization of the membrane Hamiltonians. The mass gap is shown to be
naturally organized as an expansion in a 'hidden' parameter, which turns out to
be : d being the related to the dimensionality of the background
space. We then proceed to develop a large perturbation theory for the
membrane/matrix-model Hamiltonians around the quantum/mass corrected effective
potential. The same parameter that controls the perturbation theory for the
mass gap is also shown to control the Hamiltonian perturbation theory around
the effective potential. The large perturbation theory is then translated
into the language of quantum spin chains and the one loop spectra of various
Bosonic matrix models are computed by applying the Bethe ansatz to the one-loop
effective Hamiltonians for membranes in flat space times. Apart from membranes
in flat spacetimes, the recently proposed matrix models (hep-th/0607005) for
non-critical membranes in plane wave type spacetimes are also analyzed within
the paradigm of quantum spin chains and the Bosonic sectors of all the models
proposed in (hep-th/0607005) are diagonalized at the one-loop level.Comment: 36 Page
Quark confinement: dual superconductor picture based on a non-Abelian Stokes theorem and reformulations of Yang-Mills theory
The purpose of this paper is to review the recent progress in understanding
quark confinement. The emphasis of this review is placed on how to obtain a
manifestly gauge-independent picture for quark confinement supporting the dual
superconductivity in the Yang-Mills theory, which should be compared with the
Abelian projection proposed by 't Hooft. The basic tools are novel
reformulations of the Yang-Mills theory based on change of variables extending
the decomposition of the Yang-Mills field due to Cho, Duan-Ge and
Faddeev-Niemi, together with the combined use of extended versions of the
Diakonov-Petrov version of the non-Abelian Stokes theorem for the
Wilson loop operator. Moreover, we give the lattice gauge theoretical versions
of the reformulation of the Yang-Mills theory which enables us to perform the
numerical simulations on the lattice. In fact, we present some numerical
evidences for supporting the dual superconductivity for quark confinement. The
numerical simulations include the derivation of the linear potential for static
interquark potential, i.e., non-vanishing string tension, in which the
"Abelian" dominance and magnetic monopole dominance are established,
confirmation of the dual Meissner effect by measuring the chromoelectric flux
tube between quark-antiquark pair, the induced magnetic-monopole current, and
the type of dual superconductivity, etc. In addition, we give a direct
connection between the topological configuration of the Yang-Mills field such
as instantons/merons and the magnetic monopole.Comment: 304 pages; 62 figures and 13 tables; a version published in Physics
Reports, including corrections of errors in v
Slow Switching in Globally Coupled Oscillators: Robustness and Occurrence through Delayed Coupling
The phenomenon of slow switching in populations of globally coupled
oscillators is discussed. This characteristic collective dynamics, which was
first discovered in a particular class of the phase oscillator model, is a
result of the formation of a heteroclinic loop connecting a pair of clustered
states of the population. We argue that the same behavior can arise in a wider
class of oscillator models with the amplitude degree of freedom. We also argue
how such heteroclinic loops arise inevitably and persist robustly in a
homogeneous population of globally coupled oscillators. Although the
heteroclinic loop might seem to arise only exceptionally, we find that it
appears rather easily by introducing the time-delay in the population which
would otherwise exhibit perfect phase synchrony. We argue that the appearance
of the heteroclinic loop induced by the delayed coupling is then characterized
by transcritical and saddle-node bifurcations. Slow switching arises when the
system with a heteroclinic loop is weakly perturbed. This will be demonstrated
with a vector model by applying weak noises. Other types of weak
symmetry-breaking perturbations can also cause slow switching.Comment: 10 pages, 14 figures, RevTex, twocolumn, to appear in Phys. Rev.
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