55 research outputs found

### Witten effect in a crystalline topological insulator

It has been noted a long time ago that a term of the form theta (e^2/2\pi h)
B dot E may be added to the standard Maxwell Lagrangian without modifying the
familiar laws of electricity and magnetism. theta is known to particle
physicists as the 'axion' field and whether or not it has a nonzero expectation
value in vacuum remains a fundamental open question of the Standard Model. A
key manifestation of the axion term is the Witten effect: a unit magnetic
monopole placed inside a medium with non-zero theta is predicted to bind a
(generally fractional) electric charge -e(theta/2 pi+n) with n integer. Here we
conduct a first test of the Witten effect, based on the recently established
fact that the axion term with theta=pi emerges naturally in the description of
the electromagnetic response of a new class of crystalline solids called
topological insulators - materials distinguished by strong spin-orbit coupling
and non-trivial band structure. Using a simple physical model for a topological
insulator, we demonstrate the existence of a fractional charge bound to a
monopole by an explicit numerical calculation. We also propose a scheme for
generating an 'artificial' magnetic monopole in a topological insulator film,
that may be used to facilitate the first experimental test of Witten's
prediction.Comment: 7 pages, 2 figures. Version to appear in PRB; minor changes,
discussion of several issues expande

### Axially symmetric Yang-Mills-Higgs solutions in AdS spacetime

We consider axially symmetric solutions of SU(2) Yang-Mills-Higgs theory in
globally AdS spacetime and a fixed Schwarzschild-AdS black hole background. The
solutions are characterized by two integers $(m,n)$ where $m$ is related to the
polar angle and $n$ to the azimuthal angle. Two types of finite energy, regular
configurations are considered: solutions with net magnetic charge $n>1$ and
monopole-antimonopole pairs and chains with zero net magnetic charge. The
configurations are endowed with an electric charge and carry also a
nonvanishing angular momentum density.Comment: 13 pages, 3 figure

### Embedded monopoles in quark eigenmodes in SU(2) Yang-Mills Theory

We study the embedded QCD monopoles (``quark monopoles'') using low-lying
eigenmodes of the overlap Dirac operator in zero- and finite-temperature SU(2)
Yang-Mills theory on the lattice. These monopoles correspond to the
gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles
were suggested to be agents of the chiral symmetry restoration since their
cores should suppress the chiral condensate. We study numerically the scalar,
axial and chirally invariant definitions of the embedded monopoles and show
that the monopole densities are in fact globally anti-correlated with the
density of the Dirac eigenmodes. We observe, that the embedded monopoles
corresponding to low-lying Dirac eigenvalues are dense in the chirally
invariant (high temperature) phase and dilute in the chirally broken (low
temperature) phase. We find that the scaling of the scalar and axial monopole
densities towards the continuum limit is similar to the scaling of the
string-like objects while the chirally invariant monopoles scale as membranes.
The excess of gluon energy at monopole positions reveals that the embedded QCD
monopole possesses a gluonic core, which is, however, empty at the very center
of the monopole.Comment: 29 pages, 27 figures, RevTeX 4.0; revised to match the published
version (clarifying remarks, references and acknowledgments are added

### Oscillons in gapless theories

We show that large scale oscillons, i.e., quasiperiodic, long-living particlelike solutions, may exist in massless theories, too. Their existence is explained using an effective (smeared) mass threshold which takesinto account nonlinear (finite) perturbations

### Twisted toroidal vortex-solitons in inhomogeneous media with repulsive nonlinearity

Toroidal modes in the form of so-called Hopfions, with two independent
winding numbers, a hidden one (twist, s), which characterizes a circular vortex
thread embedded into a three-dimensional soliton, and the vorticity around the
vertical axis m, appear in many fields, including the field theory,
ferromagnetics, and semi- and superconductors. Such topological states are
normally generated in multi-component systems, or as trapped quasi-linear modes
in toroidal potentials. We uncover that stable solitons with this structure can
be created, without any linear potential, in the single-component setting with
the strength of repulsive nonlinearity growing fast enough from the center to
the periphery, for both steep and smooth modulation profiles. Toroidal modes
with s=1 and vorticity m=0,1,2 are produced. They are stable for m<=1, and do
not exist for s>1. An approximate analytical solution is obtained for the
twisted ring with s=1, m=0. Under the application of an external torque, it
rotates like a solid ring. The setting can be implemented in BEC, by means of
the Feshbach resonance controlled by inhomogene-ous magnetic fields.Comment: 12 pages, 5 figures, to appear in Physical Review Letter

### Electric Flux Tube in Magnetic Plasma

In this paper we study a methodical problem related to the magnetic scenario
recently suggested and initiated by the authors \cite{Liao_ES_mono} to
understand the strongly coupled quark-gluon plasma (sQGP): the electric flux
tube in monopole plasma. A macroscopic approach, interpolating between Bose
condensed (dual superconductor) and classical gas medium is developed first.
Then we work out a microscopic approach based on detailed quantum mechanical
calculation of the monopole scattering on electric flux tube, evaluating
induced currents for all partial waves. As expected, the flux tube looses its
stability when particles can penetrate it: we make this condition precise by
calculating the critical value for the product of the flux tube size times the
particle momentum, above which the flux tube dissolves. Lattice static
potentials indicate that flux tubes seem to dissolve at $T>T_{dissolution}
\approx 1.3 T_c$. Using our criterion one gets an estimate of the magnetic
density $n\approx 4.4 \sim 6.6 fm^{-3}$ at this temperature.Comment: New version with new referecences added and minor changes. 15 pages,
8 figure

### Chains of Boson Stars

We study axially symmetric multi-soliton solutions of a complex scalar field
theory with a sextic potential, minimally coupled to Einstein's gravity. These
solutions carry no angular momentum and can be classified by the number of
nodes of the scalar field, $k_z$, along the symmetry axis; they are interpreted
as chains with $k_z+1$ boson stars, bound by gravity, but kept apart by
repulsive scalar interactions. Chains with an odd number of constituents show a
spiraling behavior for their ADM mass (and Noether charge) in terms of their
angular frequency, similarly to a single fundamental boson star, as long as the
gravitational coupling is small; for larger coupling, however, the inner part
of the spiral is replaced by a merging with the fundamental branch of radially
excited spherical boson stars. Chains with an even number of constituents
exhibit a truncated spiral pattern, with only two or three branches, ending at
a limiting solution with finite values of ADM mass and Noether charge.Comment: 20 pages, 6 figure

### Radiation of an electric charge in the field of a magnetic monopole

We consider the radiation of photons from quarks scattering on color-magnetic
monopoles in the Quark-Gluon Plasma. We consider a temperature regime
T\gsim2T_c, where monopoles can be considered as static, rare objects
embedded into matter consisting mostly of the usual "electric" quasiparticles,
quarks and gluons. The calculation is performed in the classical,
non-relativistic approximation and results are compared to photon emission from
Coulomb scattering of quarks, known to provide a significant contribution to
the photon emission rates from QGP. The present study is a first step towards
understanding whether this scattering process can give a sizeable contribution
to dilepton production in heavy-ion collisions. Our results are encouraging: by
comparing the magnitudes of the photon emission rate for the two processes, we
find a dominance in the case of quark-monopole scattering. Our results display
strong sensitivity to finite densities of quarks and monopoles.Comment: 28 pages, 8 figure

### Multikink scattering in the ϕ6 model revisited

Antikink-kink (KK) collisions in the ¯ ϕ6 model exhibit resonant scattering although the ϕ6 kinks do not support any bound states to which energy could be transferred. In P. Dorey et al. [Kink-Antikink Collisions in the ϕ6 Model, Phys. Rev. Lett. 107, 091602 (2011)] it was conjectured that, instead, energy is transferred to a collective bound mode of the full KK configuration. Here we present further strong evidence for this ¯ conjecture. Further, we construct a collective coordinate model (CCM) for KK scattering based on this ¯ collective bound mode trapped between the KK pair which allows us to reproduce the full dynamics of ¯ KK¯ scattering with striking accuracy. We also study kink-antikink (KK) scattering and its description by a ¯ CCM. In this case a significant role of radiation is discovered

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