Nontrivial Field Strength Research Articles

Neutron magnetic polarizability with Landau mode operators

The application of a uniform background magnetic field makes standard quark operators utilising gauge-covariant Gaussian smearing inefficient at isolating the ground state nucleon at nontrivial field strengths. In the absence of QCD interactions, Landau modes govern the quark energy levels. There is evidence that residual Landau mode effects remain when the strong interaction is turned on. Here we introduce novel quark operators constructed from the two-dimensional $U(1)$ Laplacian eigenmodes that describe the Landau levels of a charged particle on a periodic finite lattice. These eigenmode-projected quark operators provide enhanced precision for calculating nucleon energy shifts in a magnetic field. Using asymmetric source and sink operators, we are able to encapsulate the predominant effects of both the QCD and QED interactions in the interpolating fields for the neutron. The neutron magnetic polarizability is calculated using these techniques on the $32^3 \times 64$ dynamical QCD lattices provided by the PACS-CS Collaboration. In conjunction with a chiral effective-field theory analysis, we obtain a neutron magnetic polarizability of $\beta^n = 2.05(25)(19) \times 10^{-4}$ fm$^3$, where the numbers in parentheses describe statistical and systematic uncertainties.

Background field Landau mode operators for the nucleon

The introduction of a uniform background magnetic field breaks threedimensional spatial symmetry for a charged particle and introduces Landau mode effects. Standard quark operators are inefficient at isolating the nucleon correlation function at nontrivial field strengths. We introduce novel quark operators constructed from the twodimensional Laplacian eigenmodes that describe a charged particle on a finite lattice. These eigenmode-projected quark operators provide enhanced precision for calculating nucleon energy shifts in a magnetic field. Preliminary results are obtained for the neutron and proton magnetic polarisabilities using these methods.

Erratum: Unwinding of strings thrown into a fuzzball

The traditional black hole has a horizon, with a singularity inside the horizon. But actual microstates of black holes are `fuzzballs', with no horizon and a complex internal structure. We take the simplest hole in string theory -- the extremal 2-charge D1D5 hole -- and study a simple effect that is a consequence of this internal structure of the fuzzball. Suppose we have a NS1 string wrapping the compact circle of the fuzzball solution. In the traditional black hole solution this circle is directly tensored with the remaining directions, and does not shrink to zero size. Thus a part of the string can fall behind the horizon, but not `unwind'. In the fuzzball geometry, this circle makes a nontrivial geometric structure -- the KK monople -- by mixing with the other directions, and thus shrinks to zero at the core of the monopole. Thus the string can `unwind' in the fuzzball geometry, and the winding charge is then manifested by a nontrivial field strength living on the microstate solution. We compute this field strength for a generic microstate, and comment briefly on the physics suggested by the unwinding process.

Unwinding of strings thrown into a fuzzball

The traditional black hole has a horizon, with a singularity inside the horizon. But actual microstates of black holes are ‘fuzzballs’, with no horizon and a complex internal structure. We take the simplest hole in string theory—the extremal 2-charge D1D5 hole— and study a simple effect that is a consequence of this internal structure of the fuzzball. Suppose we have a NS1 string wrapping the compact circle of the fuzzball solution. In the traditional black hole solution this circle is directly tensored with the remaining directions, and does not shrink to zero size. Thus a part of the string can fall behind the horizon, but not ‘unwind’. In the fuzzball geometry, this circle makes a nontrivial geometric structure — the KK monople — by mixing with the other directions, and thus shrinks to zero at the core of the monopole. Thus the string can ‘unwind’ in the fuzzball geometry, and the winding charge is then manifested by a nontrivial field strength living on the microstate solution. We compute this field strength for a generic microstate, and comment briefly on the physics suggested by the unwinding process.

On stable, compactifying classical solutions of Einstein-Yang-Mills systems in 4+d spacetime dimensions

We consider the field equations at Einstein-Yang-Mills system in 4+d dimensions under the assumption that the metric corresponds to a spacetime configurationM4×(S/R), withS/R a compact coset space. Imposing a requirement thatM4 be a solution to the vacuum Einstein equations in 4-dimensions, we see that the Yang-Mills sector takes a form familiar from coset-space dimensional reduction (CSDR) schemes, but with non-trivial field strengths on the coset-space. This indicates that the symmetry groupS of the coset-space must not be isomorphic to a subgroup of the gauge groupG in 4+d dimensions, which corresponds in general to a non-trivial type of CSDR schemes. We then investigate such CSDR schemes and are able to find a new class of solutions, which permit the generation of tachyon-free solutions to the full E-Y-M system in a (large) subclass of cases.