50,071 research outputs found

    Effective couplings approach to neutralino dark matter relic density

    Full text link
    In this work, we analyze the electroweak loop corrections to the Neutralino dark matter relic density in the framework of effective coupling. In the first part, we comment on the generic features of the corrections and quantitative changes to the predicted relic density. We analyze the correlation between the characteristics of effective couplings to the nature of neutralino. Effective couplings, however, absorb only the most dominant one loop corrections and are not an exact calculation. In the second part, we assess the validity of effective couplings by comparing them to the full one loop calculations in various regions of parameter space.Comment: Moriond EW 2012 proceedings, 4 pages, 2 figure

    Instruments on large optical telescopes -- A case study

    Get PDF
    In the distant past, telescopes were known, first and foremost, for the sizes of their apertures. Advances in technology are now enabling astronomers to build extremely powerful instruments to the extent that instruments have now achieved importance comparable or even exceeding the usual importance accorded to the apertures of the telescopes. However, the cost of successive generations of instruments has risen at a rate noticeably above that of the rate of inflation. Here, given the vast sums of money now being expended on optical telescopes and their instrumentation, I argue that astronomers must undertake "cost-benefit" analysis for future planning. I use the scientific output of the first two decades of the W. M. Keck Observatory as a laboratory for this purpose. I find, in the absence of upgrades, that the time to reach peak paper production for an instrument is about six years. The prime lifetime of instruments (sans upgrades), as measured by citations returns, is about a decade. Well thought out and timely upgrades increase and sometimes even double the useful lifetime. I investigate how well instrument builders are rewarded. I find acknowledgements ranging from almost 100% to as low as 60%. Next, given the increasing cost of operating optical telescopes, the management of existing observatories continue to seek new partnerships. This naturally raises the question "What is the cost of a single night of telescope time". I provide a rational basis to compute this quantity. I then end the paper with some thoughts on the future of large ground-based optical telescopes, bearing in mind the explosion of synoptic precision photometric, astrometric and imaging surveys across the electromagnetic spectrum, the increasing cost of instrumentation and the rise of mega instruments.Comment: Revised from previous submission (typos fixed, table 6 was garbled). Submitted to PAS
    • …
    corecore