6930144
GRAVITY FROM A MODIFIED COMMUTATOR
We show that a suitably chosen position-momentum commutator can elegantly describe many features of gravity, including the IR/UV correspondence and dimensional reduction ("holography"). Using the most simplistic example based on dimensional analysis of black holes, we construct a commutator which qualitatively exhibits these novel properties of gravity. Dimensional reduction occurs because the quanta size grow quickly with momenta, and thus cannot be "packed together" as densely as naively expected. We conjecture that a more precise form of this commutator should be able to quantitatively reproduce all of these features.
118874471
Model-Independent Signatures of New Physics in non-Gaussianity
Instituut-Lorentz for Theoretical Physics, University of Leiden, Leiden 2333CA, The Netherlands(Dated: February 6, 2012)We compute the model-independent contributions to the primordial bispectrum and trispectrum inde Sitter space due to high-energy physics. We do this by coupling a light inaton to an auxiliaryheavy eld, and then evaluating correlation functions in the Schwinger-Keldysh \in-in" formalism.The high-energy physics produces corrections parametrized by H=Mwhere His the scale of ina-tion and M is the mass of the heavy eld. The bispectrum peaks near the elongated shape, butotherwise contains no features. On the other hand, the trispectrum contains oscillations which areof a magnitude possibly detectable using upcoming data. These oscillations are the cosmologicalanalogue of energy eigenstate mixing.
84839474
Model-Independent Signatures of New Physics in Slow-Roll Inflation
We compute the universal generic corrections to the power spectrum in slow-roll inflation due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the "in-in" formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. The density power spectrum is universally modified at leading order in $H/M$, the ratio of the scale of inflation to the scale of new physics; the tensor power spectrum receives only subleading corrections. In doing so, we show how to make sense of a physical momentum-cut-off in loop integrals despite dynamical redshifts, and how the result can be captured in a combined effective action/effective density matrix, where the latter contains non-adiabatic terms which modify the boundary conditions.
16292932
The stability of noncommutative scalar solitons
We determine the stability conditions for a radially symmetric non-commutative scalar soliton at finite noncommutivity parameter θ. We find an intriguing relationship between the stability and existence conditions for all level-1 solutions, in that they all have nearly-vanishing stability eigenvalues at critical θm2. The stability or non-stability of the system may then be determined entirely by the 3 coefficient in the potential. For higher-level solutions we find an ambiguity in extrapolating solutions to finite θ which prevents us from making any general statements. For these stability may be determined by comparing the fluctuation eigenvalues to critical values which we calculate.
15602764
Two black hole holography, lensing, and intensity
We numerically verify the analysis of the 'expanding horizon' theory of Susskind in relation to the 't Hooft holographic conjecture. By using a numerical simulation to work out the holographic image formed by two black holes upon a screen very far away, it is seen that it is impossible for a horizon to hide behind another. We also compute the holographic intensity distribution of such an arrangement.
13946666
A Quantum Mechanical Model of Spherical Supermembranes
We present a quantum mechanical model of spherical supermembranes. Using superfields to represent the cartesian coordinates of the membrane, we are able to exactly determine its supersymmetric vacua. We find there are two classical vacua, one corresponding to an extended membrane and one corresponding to a point-like membrane. For the = 2 case, instanton effects then lift these vacua to massive states. For the = 4 case, there is no instanton tunneling, and the vacua remain massless. Similarities to spherical supermembranes as giant gravitons and in Matrix theory on pp-waves is discussed.
118351795
Balloon-borne hard X-ray astronomy with PoGOLite: Opening a new window on the universe
High energy polarization can be an indication of geometry, orientation, and other physical phenomena for a variety of sources, but has heretofore been a virtually unmeasured phenomenon. PoGOLite is a balloon-borne instrument intended to measure the polarization of X-rays between 25 and 100 keV. The pathfinder version of the instrument is scheduled to be launched from northern Sweden in summer 2013. The primary targets are the Crab pulsar and nebula and Cygnus X-1.
16544780
XMM-Newton, Chandra, and CGPS observations of the Supernova Remnants G85.4+0.7 and G85.9–0.6
We present an XMM-Newton detection of two low radio surface brightness supernova remnants (SNRs), G85.4+0.7 and G85.9–0.6, discovered with the Canadian Galactic Plane Survey (CGPS). High-resolution XMM-Newton images revealing the morphology of the diffuse emission, as well as discrete point sources, are presented and correlated with radio and Chandra images. The new data also permit a spectroscopic analysis of the diffuse emission regions, and a spectroscopic and timing analysis of the point sources. Distances have been determined from H I and CO data to be 3.5 ± 1.0 kpc for SNR G85.4+0.7 and 4.8 ± 1.6 kpc for SNR G85.9–0.6. The SNR G85.4+0.7 is found to have a temperature of ~12-13 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1033D23.5 erg s−1 (where D3.5 is the distance in units of 3.5 kpc), with an electron density ne of ~(0.07–0.16) (fD3.5)−1/2 cm−3 (where f is the volume filling factor) and a shock age of ~(9–49) (fD3.5)1/2 kyr. The SNR G85.9–0.6 is found to have a temperature of ~15-19 MK and a 0.5-2.5 keV luminosity of ~(1–4) × 1034D24.8 erg s−1 (where D4.8 is the distance in units of 4.8 kpc), with an electron density ne of ~(0.04–0.10) (fD4.8)−1/2 cm−3 and a shock age of ~(12–42) (fD4.8)1/2 kyr. Based on the data presented here, none of the point sources appears to be the neutron star associated with either SNR.
23294225
A balloon-borne measurement of high latitude atmospheric neutrons using a licaf neutron detector
PoGOLino is a scintillator-based neutron detector. Its main purpose is to provide data on the neutron flux in the upper stratosphere at high latitudes at thermal and non-thermal energies for the PoGOLite instrument. PoGOLite is a balloon borne hard X-ray polarimeter for which the main source of background stems from high energy neutrons. No measurements of the neutron environment for the planned flight latitude and altitude exist. Furthermore this neutron environment changes with altitude, latitude and solar activity, three variables that will vary throughout the PoGOLite flight. PoGOLino was developed to study the neutron environment and the influences from these three variables upon it. PoGOLino consists of two Europium doped Lithium Calcium Aluminium Fluoride (Eu:LiCAF) scintillators, each of which is sandwiched between 2 Bismuth Germanium Oxide (BGO) scintillating crystals, which serve to veto signals produced by gamma-rays and charged particles. This allows the neutron flux to be measured even in high radiation environments. Measurements of neutrons in two separate energy bands are achieved by placing one LiCAF detector inside a moderating polyethylene shield while the second detector remains unshielded. The PoGOLino instrument was launched on March 20th 2013 from the Esrange Space Center in Northern Sweden to an altitude of 30.9 km. A description of the detector design and read-out system is presented. A detailed set of simulations of the atmospheric neutron environment performed using both PLANETOCOSMICS and Geant4 will also be described. The comparison of the neutron flux measured during flight to predictions based on these simulations will be presented and the consequences for the PoGOLite background will be discussed.
41092140
Balloon-borne hard X-ray polarimetry with PoGOLite
PoGOLite is a hard X-ray polarimeter operating in the 25-100 keY energy band. The instrument design is optimised for the observation of compact astrophysical sources. Observations are conducted from a stabilised stratospheric balloon platform at an altitude of approximately 40 km. The primary targets for first balloon flights of a reduced effective area instrument are the Crab and Cygnus-Xl. The polarisation of incoming photons is determined using coincident Compton scattering and photoabsorption events reconstructed in an array of plastic scintillator detector cells surrounded by a bismuth germanate oxide (BGO) side anticoincidence shield and a polyethylene neutron shield. A custom attitude control system keeps the polarimeter field-of-view aligned to targets of interest, compensating for sidereal motion and perturbations such as torsional forces in the balloon rigging. An overview of the PoGOLite project is presented and the outcome of the ill-fated maiden balloon flight is discussed.