395 research outputs found
Strings in Yang-Mills-Higgs theory coupled to gravity
Non-Abelian strings for an Einstein-Yang-Mills-Higgs theory are explicitly
constructed. We consider N_f Higgs fields in the fundamental representation of
the U(1)xSU(N_c) gauge group in order to have a color-flavor SU(N_c) group
remaining unbroken. Choosing a suitable ansatz for the metric, Bogomol'nyi-like
first order equations are found and rotationally symmetric solutions are
proposed. In the N_f = N_c case, solutions are local strings and are shown to
be truly non-Abelian by parameterizing them in terms of orientational
collective coordinates. When N_f > N_c, the solutions correspond to semilocal
strings which, beside the orientational degrees of freedom, acquire additional
collective coordinates parameterizing their transverse size. The low-energy
effective theories for the correspondent moduli are found, showing that all
zero modes are normalizable in presence of gravity, even in the semilocal case.Comment: 20 pages, no figure, modified version with new title, abstract and an
additional section completing the study of effective theories. Physical
Review D in pres
Asymptotic behaviour of multiple scattering on infinite number of parallel demi-planes
The exact solution for the scattering of electromagnetic waves on an infinite
number of parallel demi-planes has been obtained by J.F. Carlson and A.E. Heins
in 1947 using the Wiener-Hopf method. We analyze their solution in the
semiclassical limit of small wavelength and find the asymptotic behaviour of
the reflection and transmission coefficients. The results are compared with the
ones obtained within the Kirchhoff approximation
Axially Symmetric Solutions for SU(2) Yang-Mills Theory
By casting the Yang-Mills-Higgs equations of an SU(2) theory in the form of
the Ernst equations of general relativity, it is shown how the known exact
solutions of general relativity can be used to give similiar solutions for
Yang-Mills theory. Thus all the known exact solutions of general relativity
with axial symmetry (e.g. the Kerr metric, the Tomimatsu-Sato metric) have
Yang-Mills equivalents. In this paper we only examine in detail the Kerr-like
solution. It will be seen that this solution has surfaces where the gauge and
scalar fields become infinite, which correspond to the infinite redshift
surfaces of the normal Kerr solution. It is speculated that this feature may be
connected with the confinement mechanism since any particle which carries an
SU(2) color charge would tend to become trapped once it passes these surfaces.
Unlike the Kerr solution, our solution apparently does not have any intrinsic
angular momentum, but rather appears to give the non-Abelian field
configuration associated with concentric shells of color charge.Comment: 15 pages LaTe
Semi-classical calculations of the two-point correlation form factor for diffractive systems
The computation of the two-point correlation form factor K(t) is performed
for a rectangular billiard with a small size impurity inside for both periodic
or Dirichlet boundary conditions. It is demonstrated that all terms of
perturbation expansion of this form factor in powers of t can be computed
directly by semiclassical trace formula. The main part of the calculation is
the summation of non-diagonal terms in the cross product of classical orbits.
When the diffraction coefficient is a constant our results coincide with
expansion of exact expressions ontained by a different method.Comment: 42 pages, 10 figures, Late
Non-Abelian Semilocal Strings in N=2 Supersymmetric QCD
We consider a benchmark bulk theory in four-dimensions: N=2 supersymmetric
QCD with the gauge group U(N) and N_f flavors of fundamental matter
hypermultiplets (quarks). The nature of the BPS strings in this benchmark
theory crucially depends on N_f. If N_f\geq N and all quark masses are equal,
it supports non-Abelian BPS strings which have internal (orientational) moduli.
If N_f>N these strings become semilocal, developing additional moduli \rho
related to (unlimited) variations of their transverse size.
Using the U(2) gauge group with N_f=3,4 as an example, we derive an effective
low-energy theory on the (two-dimensional) string world sheet. Our derivation
is field-theoretic, direct and explicit: we first analyze the Bogomol'nyi
equations for string-geometry solitons, suggest an ansatz and solve it at large
\rho. Then we use this solution to obtain the world-sheet theory.
In the semiclassical limit our result confirms the Hanany-Tong conjecture,
which rests on brane-based arguments, that the world-sheet theory is N=2
supersymmetric U(1) gauge theory with N positively and N_e=N_f-N negatively
charged matter multiplets and the Fayet-Iliopoulos term determined by the
four-dimensional coupling constant. We conclude that the Higgs branch of this
model is not lifted by quantum effects. As a result, such strings cannot
confine.
Our analysis of infrared effects, not seen in the Hanany-Tong consideration,
shows that, in fact, the derivative expansion can make sense only provided the
theory under consideration is regularized in the infrared, e.g. by the quark
mass differences. The world-sheet action discussed in this paper becomes a bona
fide low-energy effective action only if \Delta m_{AB}\neq 0.Comment: 36 pages, no figure
Deconstructing Supersymmetry
Two supersymmetric classical mechanical systems are discussed. Concrete
realizations are obtained by supposing that the dynamical variables take values
in a Grassmann algebra with two generators. The equations of motion are
explicitly solved.Comment: 19 pages, Tex fil
Geodesic motion in the space-time of cosmic strings interacting via magnetic fields
We study the geodesic motion of test particles in the space-time of two
Abelian-Higgs strings interacting via their magnetic fields. These bound states
of cosmic strings constitute a field theoretical realization of p-q-strings
which are predicted by inflationary models rooted in String Theory, e.g. brane
inflation. In contrast to previously studied models describing p-q-strings our
model possesses a Bogomolnyi-Prasad-Sommerfield (BPS) limit. If cosmic strings
exist it would be exciting to detect them by direct observation. We propose
that this can be done by the observation of test particle motion in the
space-time of these objects. In order to be able to make predictions we have to
solve the field equations describing the configuration as well as the geodesic
equation numerically. The geodesics can then be classified according to the
test particle's energy, angular momentum and momentum along the string axis. We
find that the interaction of two Abelian-Higgs strings can lead to the
existence of bound orbits that would be absent without the interaction. We also
discuss the minimal and maximal radius of orbits and comment on possible
applications in the context of gravitational wave emission.Comment: v1: 22 pages including 17 figures; v2: new figure added, section on
observables added; acccepted for publication in Phys. Rev.
Electromagnetic Interaction in the System of Multimonopoles and Vortex Rings
Behavior of static axially symmetric monopole-antimonopole and vortex ring
solutions of the SU(2) Yang-Mills-Higgs theory in an external uniform magnetic
field is considered. It is argued that the axially symmetric
monopole-antimonopole chains and vortex rings can be treated as a bounded
electromagnetic system of the magnetic charges and the electric current rings.
The magnitude of the external field is a parameter which may be used to test
the structure of the static potential of the effective electromagnetic
interaction between the monopoles with opposite orientation in the group space.
It is shown that for a non-BPS solutions there is a local minimum of this
potential.Comment: 10 pages, 12 figures, some minor corrections, version to appear in
Phys. Rev.
Analogies between self-duality and stealth matter source
We consider the problem of a self-interacting scalar field nonminimally
coupled to the three-dimensional BTZ metric such that its energy-momentum
tensor evaluated on the BTZ metric vanishes. We prove that this system is
equivalent to a self-dual system composed by a set of two first-order
equations. The self-dual point is achieved by fixing one of the coupling
constant of the potential in terms of the nonminimal coupling parameter. At the
self-dual point and up to some boundary terms, the matter action evaluated on
the BTZ metric is bounded below and above. These two bounds are saturated
simultaneously yielding to a vanishing action for configurations satisfying the
set of self-dual first-order equations.Comment: 6 pages. To be published in Jour. Phys.
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