Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

It has been suggested that Einstein's theory of General Relativity can be modified to accomodate mismatches between the gravitational field and luminous matter on a wide range of scales. Covariant theories of modified gravity generically predict the existence of extra degrees of freedom which may be interpreted as dark matter. We study a subclass of these theories where the overall energy density in these extra degrees of freedom is subdominant relative to the baryon density and show that they favour the presence of massive neutrinos. For some specific cases (such as a flat Universes with a cosmological constant) one finds a conservative lower bound on the neutrinos mass of $m_\nu>0.31$ eV.

Abstract:

We have carried out a concept study for a wide-field monolithic integral field unit (IFU) spectrograph for extremely large telescopes (ELTs). We target in this paper the technological challenges that have to be faced in order to build such an instrument, focusing on the adaptive optics (AO) requirements, the image slicer technology, and the detectors status. We also address the main science drivers, together with the concept design and the expected performance applied to the European-ELT (E-ELT) case. A monolithic wide-field spectrograph provides a continuous field of view (FOV) separated by a field splitter in several subfields, each of them feeding a module featuring an image slicer, a collimator and a spectrograph. The use of image slicers provides 3D spectrographic images of the complete FOV, allowing for detection and study of sources without need of targeting them, a very useful property especially for the deep observation of faint high-redshift objects, whose density on the sky is expected to be quite high. In light of this discussion, we suggest the advantages of using shorter wavelengths and its implication in both the scientific program and the budget. © 2008. The Astronomical Society of the Pacific. All rights reserved.

Abstract:

We describe the objectives, design and predicted performance of Clover, which is a ground-based experiment to measure the faint ``B-mode'' polarisation pattern in the cosmic microwave background (CMB). To achieve this goal, clover will make polarimetric observations of approximately 1000 deg^2 of the sky in spectral bands centred on 97, 150 and 225 GHz. The observations will be made with a two-mirror compact range antenna fed by profiled corrugated horns. The telescope beam sizes for each band are 7.5, 5.5 and 5.5 arcmin, respectively. The polarisation of the sky will be measured with a rotating half-wave plate and stationary analyser, which will be an orthomode transducer. The sky coverage combined with the angular resolution will allow us to measure the angular power spectra between 20 < l < 1000. Each frequency band will employ 192 single polarisation, photon noise limited TES bolometers cooled to 100 mK. The background-limited sensitivity of these detector arrays will allow us to constrain the tensor-to-scalar ratio to 0.026 at 3sigma, assuming any polarised foreground signals can be subtracted with minimal degradation to the 150 GHz sensitivity. Systematic errors will be mitigated by modulating the polarisation of the sky signals with the rotating half-wave plate, fast azimuth scans and periodic telescope rotations about its boresight. The three spectral bands will be divided into two separate but nearly identical instruments - one for 97 GHz and another for 150 and 225 GHz. The two instruments will be sited on identical three-axis mounts in the Atacama Desert in Chile near Pampa la Bola. Observations are expected to begin in late 2009.