Integrability and maximally helicity violating diagrams in n=4 supersymmetric yang-mills theory.

We apply maximally helicity violating (MHV) diagrams to the derivation of the one-loop dilatation operator of N=4 supersymmetric Yang-Mills theory in the SO(6) sector. We find that in this approach the calculation reduces to the evaluation of a single MHV diagram in dimensional regularization. This provides the first application of MHV diagrams to an off-shell quantity. We also discuss other applications of the method and future directions

Generating entanglement with low Q-factor microcavities

We propose a method of generating entanglement using single photons and electron spins in the regime of resonance scattering. The technique involves matching the spontaneous emission rate of the spin dipole transition in bulk dielectric to the modified rate of spontaneous emission of the dipole coupled to the fundamental mode of an optical microcavity. We call this regime resonance scattering where interference between the input photons and those scattered by the resonantly coupled dipole transition result in a reflectivity of zero. The contrast between this and the unit reflectivity when the cavity is empty allow us to perform a non demolition measurement of the spin and to non deterministically generate entanglement between photons and spins. The chief advantage of working in the regime of resonance scattering is that the required cavity quality factors are orders of magnitude lower than is required for strong coupling, or Purcell enhancement. This makes engineering a suitable cavity much easier particularly in materials such as diamond where etching high quality factor cavities remains a significant challenge

Low-temperature behavior of the statistics of the overlap distribution in Ising spin-glass models

Using Monte Carlo simulations, we study in detail the overlap distribution for individual samples for several spin-glass models including the infinite-range Sherrington-Kirkpatrick model, short-range Edwards-Anderson models in three and four space dimensions, and one-dimensional long-range models with diluted power-law interactions. We study three long-range models with different powers as follows: the first is approximately equivalent to a short-range model in three dimensions, the second to a short-range model in four dimensions, and the third to a short-range model in the mean-field regime. We study an observable proposed earlier by some of us which aims to distinguish the "replica symmetry breaking" picture of the spin-glass phase from the "droplet picture," finding that larger system sizes would be needed to unambiguously determine which of these pictures describes the low-temperature state of spin glasses best, except for the Sherrington-Kirkpatrick model which is unambiguously described by replica symmetry breaking. Finally, we also study the median integrated overlap probability distribution and a typical overlap distribution, finding that these observables are not particularly helpful in distinguishing the replica symmetry breaking and the droplet pictures.Comment: 11 pages, 6 figure

Long-term Observations of Three Nulling Pulsars

We present an analysis of approximately 200 hours of observations of the pulsars J1634$-$5107, J1717$-$4054 and J1853$+$0505, taken over the course of 14.7 yr. We show that all of these objects exhibit long term nulls and radio-emitting phases (i.e. minutes to many hours), as well as considerable nulling fractions (NFs) in the range $\sim67\,\% - 90\,\%$. PSR J1717$-$4054 is also found to exhibit short timescale nulls ($1 - 40~P$) and burst phases ($\lesssim 200~P$) during its radio-emitting phases. This behaviour acts to modulate the NF, and therefore the detection rate of the source, over timescales of minutes. Furthermore, PSR J1853$+$0505 is shown to exhibit a weak emission state, in addition to its strong and null states, after sufficient pulse integration. This further indicates that nulls may often only represent transitions to weaker emission states which are below the sensitivity thresholds of particular observing systems. In addition, we detected a peak-to-peak variation of $33\pm1\,\%$ in the spin-down rate of PSR J1717$-$4054, over timescales of hundreds of days. However, no long-term correlation with emission variation was found.Comment: 10 pages, 8 figures, accepted for publication in MNRA

Quasiparticle Trapping in Microwave Kinetic Inductance Strip Detectors

Microwave Kinetic Inductance Detectors (MKIDs) are thin-film, superconducting resonators, which are attractive for making large detector arrays due to their natural frequency domain multiplexing at GHz frequencies. For X-ray to IR wavelengths, MKIDs can provide high-resolution energy and timing information for each incoming photon. By fabricating strip detectors consisting of a rectangular absorber coupled to MKIDs at each end, high quantum efficiency and spatial resolution can be obtained. A similar geometry is being pursued for phonon sensing in a WIMP dark matter detector. Various materials have been tested including tantalum, tin, and aluminum for the absorbing strip, and aluminum, titanium, and aluminum manganese for the MKID. Initial Ta/Al X-ray devices have shown energy resolutions as good as 62 eV at 6 keV. A Ta/Al UV strip detector with an energy resolution of 0.8 eV at 4.9 eV has been demonstrated, but we find the coupling of the MKIDs to the absorbers is unreliable for these thinner devices. We report on progress probing the thicknesses at which the absorber/MKID coupling begins to degrade by using a resonator to inject quasiparticles directly into the absorber. In order to eliminate the absorber/MKID interface, a modified design for implanted AlMn/Al UV strip detectors was developed, and results showing good transmission of quasiparticles from the absorber to MKID in these devices are presented

On the Apparent Nulls and Extreme Variability of PSR J1107-5907

We present an analysis of the emission behaviour of PSR J1107-5907, a source known to exhibit separate modes of emission, using observations obtained over approximately 10 yr. We find that the object exhibits two distinct modes of emission; a strong mode with a broad profile and a weak mode with a narrow profile. During the strong mode of emission, the pulsar typically radiates very energetic emission over sequences of ~200-6000 pulses (~60 s-24 min), with apparent nulls over time-scales of up to a few pulses at a time. Emission during the weak mode is observed outside of these strong-mode sequences and manifests as occasional bursts of up to a few clearly detectable pulses at a time, as well as low-level underlying emission which is only detected through profile integration. This implies that the previously described null mode may in fact be representative of the bottom-end of the pulse intensity distribution for the source. This is supported by the dramatic pulse-to-pulse intensity modulation and rarity of exceptionally bright pulses observed during both modes of emission. Coupled with the fact that the source could be interpreted as a rotating radio transient (RRAT)-like object for the vast majority of the time, if placed at a further distance, we advance that this object likely represents a bridge between RRATs and extreme moding pulsars. Further to these emission properties, we also show that the source is consistent with being a near-aligned rotator and that it does not exhibit any measurable spin-down rate variation. These results suggest that nulls observed in other intermittent objects may in fact be representative of very weak emission without the need for complete cessation. As such, we argue that longer (> 1 h) observations of pulsars are required to discern their true modulation properties.Comment: 15 pages, 10 figures, accepted for publication in MNRA

Primordial Black Hole: Mass and Angular Momentum Evolution

The evolution of the primordial low mass black hole (PBH) in hot universe is considered. Increase of mass and decrease of PBH spin due to the accretion of radiation dominated matter are estimated with using of results of numerical simulation of PBH formation and approximate relations for accretion to a rotating black hole.Comment: Gravitation and Cosmology, accepted, 3 pages, Talk presented at the russian summer school-seminar "Modern theoretical problems of gravitation and cosmology" (GRACOS-2007), September 9-16, 2007, Kazan-Yalchik, Russi

Truthful Facility Assignment with Resource Augmentation: An Exact Analysis of Serial Dictatorship

We study the truthful facility assignment problem, where a set of agents with private most-preferred points on a metric space are assigned to facilities that lie on the metric space, under capacity constraints on the facilities. The goal is to produce such an assignment that minimizes the social cost, i.e., the total distance between the most-preferred points of the agents and their corresponding facilities in the assignment, under the constraint of truthfulness, which ensures that agents do not misreport their most-preferred points. We propose a resource augmentation framework, where a truthful mechanism is evaluated by its worst-case performance on an instance with enhanced facility capacities against the optimal mechanism on the same instance with the original capacities. We study a very well-known mechanism, Serial Dictatorship, and provide an exact analysis of its performance. Although Serial Dictatorship is a purely combinatorial mechanism, our analysis uses linear programming; a linear program expresses its greedy nature as well as the structure of the input, and finds the input instance that enforces the mechanism have its worst-case performance. Bounding the objective of the linear program using duality arguments allows us to compute tight bounds on the approximation ratio. Among other results, we prove that Serial Dictatorship has approximation ratio $g/(g-2)$ when the capacities are multiplied by any integer $g \geq 3$. Our results suggest that even a limited augmentation of the resources can have wondrous effects on the performance of the mechanism and in particular, the approximation ratio goes to 1 as the augmentation factor becomes large. We complement our results with bounds on the approximation ratio of Random Serial Dictatorship, the randomized version of Serial Dictatorship, when there is no resource augmentation