17 research outputs found
Spectrum of two-dimensional gauge theories coupled to massless fermions in integer representations
The spectra of two-dimensional gauge theories coupled to a single
massless Majorana fermion in integer representations, , are numerically
investigated using the Discrete Light-Cone Hamiltonian. The primary aim is to
understand the presence of massless states for in spite of the absence of
a continuous symmetry. After comparing to existing results for (adjoint
fermions), we present results for . As expected, for there are
no massless states but in contrast to the theory, the lightest state is a
boson. We find exact zero modes in the bosonic and fermionic sector for all
values of total momentum for and and, in each sector, the number of
zero modes grows with the value of the total momentum. In addition to the
spectrum, we present results on the particle number and momentum fraction
distributions and argue for a separation of bulk states from edge states.Comment: 21 pages, 6 figure
Deforming Soft Algebras for Gauge Theory
Symmetry algebras deriving from towers of soft theorems can be deformed by a
short list of higher-dimension Wilsonian corrections to the effective action.
We study the simplest of these deformations in gauge theory arising from a
massless complex scalar coupled to . The soft gauge symmetry
'-algebra', compactly realized as a higher-spin current algebra acting on
the celestial sphere, is deformed and enlarged to an associative algebra
containing soft scalar generators. This deformed soft algebra is found to be
non-abelian even in abelian gauge theory. A two-parameter family of central
extensions of the -subalgebra are generated by shifting and decoupling the
scalar generators. It is shown that these central extensions can also be
generated by expanding around a certain non-trivial but Lorentz invariant
shockwave type background for the scalar field.Comment: 13 pages, 1 figur
Mapping our universe in 3D with MITEoR
Mapping our universe in 3D by imaging the redshifted 21 cm line from neutral hydrogen has the potential to overtake the cosmic microwave background as our most powerful cosmological probe, because it can map a much larger volume of our Universe, shedding new light on the epoch of reionization, inflation, dark matter, dark energy, and neutrino masses. We report on MITEoR, a pathfinder low-frequency radio interferometer whose goal is to test technologies that greatly reduce the cost of such 3D mapping for a given sensitivity. MITEoR accomplishes this by using massive baseline redundancy both to enable automated precision calibration and to cut the correlator cost scaling from N[superscript 2] to N log N, where N is the number of antennas. The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious HERA project, which incorporates many identical or similar technologies using an order of magnitude more antennas, each with dramatically larger collecting area.National Science Foundation (U.S.) (Grant AST-0908848)National Science Foundation (U.S.) (Grant AST-1105835)MIT Kavli Instrumentation FundMassachusetts Institute of Technology. Undergraduate Research Opportunities Progra
A latitude-dependent analysis of the leptonic hypothesis for the Fermi Bubbles
The Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard cosmic ray electron population within the volume of the Bubbles, via inverse Compton scattering and synchrotron radiation, respectively. The relative rates of these processes are set by the relative energy density of the interstellar radiation field and the magnetic field within the Bubbles; consequently, under the hypothesis of a common origin, the combination of the gamma-ray and microwave measurements can be used to estimate the magnetic field within the Bubbles. We revisit the consistency of this hypothesis on a latitude-by-latitude basis, using data from Fermi, WMAP and Planck; estimate the variation of the electron spectrum within the Bubbles; and infer bounds on the magnetic field within the Bubbles as a function of distance from the Galactic plane. We find that while the microwave and gamma-ray spectra are generally consistent with the leptonic hypothesis for few-microGauss magnetic fields, there appears to be a preference for spectral hardening in the microwaves at mid-latitudes (especially in the |b| ∼ 25°–35° range) that is not mirrored in the gamma-rays. This result may hint at a non-leptonic contribution to the gamma-ray spectra; however, the discrepancy can be reconciled in purely leptonic models if the cut-off energy for the electrons is lower in this latitude range and the spectrum below the cut-off is harder. Keywords: ISM: jets and outflows; gamma-rays: ISM; radio continuum: ISMUnited States. Department of Energy (Grant DE-SC00012567)United States. Department of Energy (Grant DE-SC0013999
Soft Scalars and the Geometry of the Space of Celestial CFTs
Known examples of the holographic dictionary in asymptotically Anti-de Sitter
spacetimes equate moduli spaces of bulk vacua with conformal manifolds in the
dual quantum field theory. We demonstrate that the same identification holds
for gravity in asymptotically flat spacetimes in any dimension, in accord with
expectations derived from the celestial conformal field theory (CCFT)
formalism. Soft limits of moduli scalars described by the sigma model are
universal, and relate to parallel transport of -matrix observables over the
moduli space of bulk vacua. The leading "soft moduli operator" is the shadow
transform of a dimension marginal operator . The universal
form of the soft limit guarantees that acts as a marginal deformation in
the CCFT, and coherent states of the soft scalars correspond to finite
deformations along the conformal manifold. This manifold typically has
curvature, which is captured by the antisymmetric double-soft theorem and which
reflects the Berry curvature in CCFT. We also compute the
Mellin-transformed four-point function in the sigma model and compare to a
formula of Kutasov for the curvature of the conformal manifold.Comment: 21 page