96440495
Next to subleading soft-graviton theorem in arbitrary dimensions
A bstractWe study the soft graviton theorem recently proposed by Cachazo and Strominger. We employ the Cachazo, He and Yuan formalism to show that the next to sub-leading order soft factor for gravity is universal at tree level in arbitrary dimensions.
119154326
Note on high energy scattering of open superstrings
We study the Regge and hard-scattering limits of the one-loop amplitude for massless open string states in the type I theory in flat space. For hard scattering we find the exact kinematic dependence in terms of the scattering angle of the factor multiplying the known exponential falloff, without relying on a saddle point approximation for the integration over the cross ratio. This bypasses the issues of estimating the contributions from flat directions as well as those that arise from fluctuations of the Gaussian integration about the saddle point. This result allows for a straightforward computation of the small-angle behavior of the hard-scattering regime and we find complete agreement with the Regge limit at high momentum transfer, as expected.
54974451
Type 0 open string amplitudes and the tensionless limit
Instituto de Fisica Teorica, UNESP-Universidade Estadual Paulista, Rua Dr. Bento T. Ferraz 271, Bl. II
119202259
Open string Regge trajectory and its field theory limit
We study the properties of the leading Regge trajectory in open string theory including the open string planar one-loop corrections. With $SU(N)$ Chan-Paton factors, the sum over planar open string multiloop diagrams describes the 't Hooft limit $N\ensuremath{\rightarrow}\ensuremath{\infty}$ with $N{g}_{s}^{2}$ fixed. Our motivation is to improve the understanding of open string theory at finite ${\ensuremath{\alpha}}^{\ensuremath{'}}$ as a model of gauge field theories. $SU(N)$ gauge theories in $D$ space-time dimensions are described by requiring open strings to end on a stack of $N$ $\mathrm{D}p$-branes of space-time dimension $D=p+1$. The large $N$ leading trajectory $\ensuremath{\alpha}(t)=1+{\ensuremath{\alpha}}^{\ensuremath{'}}t+\ensuremath{\Sigma}(t)$ can be extracted, through order ${g}^{2}$, from the $s\ensuremath{\rightarrow}\ensuremath{-}\ensuremath{\infty}$ limit, at fixed $t$, of the four open string tree and planar loop diagrams. We analyze the $t\ensuremath{\rightarrow}0$ behavior with the result that $\ensuremath{\Sigma}(t)\ensuremath{\sim}\ensuremath{-}C{g}^{2}(\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}t{)}^{(D\ensuremath{-}4)/2}/(D\ensuremath{-}4)$. This result precisely tracks the 1-loop Reggeized gluon of gauge theory in $Dg4$ space-time dimensions. In particular, for $D\ensuremath{\rightarrow}4$ it reproduces the known infrared divergences of gauge theory in 4 dimensions with a Regge trajectory behaving as $\ensuremath{-}\mathrm{ln}﻿(\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}t)$. We also study $\ensuremath{\Sigma}(t)$ in the limit $t\ensuremath{\rightarrow}\ensuremath{-}\ensuremath{\infty}$ and show that, when $Dl8$, it behaves as ${\ensuremath{\alpha}}^{\ensuremath{'}}t/(\mathrm{ln}﻿(\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}t){)}^{\ensuremath{\gamma}}$, where $\ensuremath{\gamma}g0$ depends on $D$ and the number of massless scalars. Thus, as long as $4lDl8$, the 1-loop correction stays small relative to the tree trajectory for $\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}t$ arbitrarily large. Finally we present the results of numerical calculations of $\ensuremath{\Sigma}(t)$ for all negative $t$.
43912743
First Results from the MIT Optical Rapid Imaging System (MORIS) on the IRTF: A Stellar Occultation by Pluto and a Transit by Exoplanet XO-2b
We present a high-speed, visible-wavelength imaging instrument: MORIS (the MIT Optical Rapid Imaging System). MORIS is mounted on the 3 m Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Its primary component is an Andor iXon camera, a nearly 60" square field of view with high quantum efficiency, low read noise, low dark current, and full-frame readout rates ranging from as slow as desired to a maximum of between 3.5 Hz and 35 Hz (depending on the mode; read noise of 6 e- pixel-1 and 49 e- pixel-1 with electron-multiplying gain = 1, respectively). User-selectable binning and subframing can increase the cadence to a few hundred hertz. An electron-multiplying mode can be employed for photon counting, effectively reducing the read noise to subelectron levels at the expense of dynamic range. Data cubes, or individual frames, can be triggered to several-nanosecond accuracy using the Global Positioning System. MORIS is mounted on the side-facing exit window of SpeX, allowing simultaneous near-infrared and visible observations. Here, we describe the components, setup, and measured characteristics of MORIS. We also report results from the first science observations: the 2008 June 24 stellar occultation by Pluto and an extrasolar planetary transit by XO-2b. The Pluto occultation of a 15.8R magnitude star has a signal-to-noise ratio of 35 per atmospheric scale height and a midtime error of 0.32 s. The XO-2b transit reaches photometric precision of 0.5 mmag in 2 minutes and has a midtime timing precision of 23 s.
11905637
The Atacama Cosmology Telescope: High-resolution Sunyaev-Zel'dovich Array Observations of ACT SZE-selected Clusters from the Equatorial Strip
We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly discovered, massive ( 1015 M ☉), high-redshift (z = 0.81) cluster revealed by ACT through the Sunyaev-Zel'dovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point-source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as A2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the 20% level for some fraction of clusters.