Single Atom Detection With Optical Cavities

We present a thorough analysis of single atom detection using optical cavities. The large set of parameters that influence the signal-to-noise ratio for cavity detection is considered, with an emphasis on detunings, probe power, cavity finesse and photon detection schemes. Real device operating restrictions for single photon counting modules and standard photodiodes are included in our discussion, with heterodyne detection emerging as the clearly favourable technique, particularly for detuned detection at high power.Comment: 11 pages, 8 figures, submitted to PRA, minor changes in Secs. I and IVD.2, and revised Fig.

Constraints on the large-x d/u ratio from electron-nucleus scattering at x>1

Recently the ratio of neutron to proton structure functions F_2n/F_2p was extracted from a phenomenological correlation between the strength of the nuclear EMC effect and inclusive electron-nucleus cross section ratios at x>1. Within conventional models of nuclear smearing, this "in-medium correction" (IMC) extraction constrains the size of nuclear effects in the deuteron structure functions, from which the neutron structure function F_2n is usually extracted. The IMC data determine the resulting proton d/u quark distribution ratio, extrapolated to x=1, to be 0.23 +- 0.09 with a 90% confidence level. This is well below the SU(6) symmetry limit of 1/2 and significantly above the scalar diquark dominance limit of 0.Comment: 4 pages, 3 figure

Universality of Leading Relativistic Corrections to Bound State Gyromagnetic Ratios

We discuss the leading relativistic (nonrecoil and recoil) corrections to bound state $g$-factors of particles with arbitrary spin. These corrections are universal for any spin and depend only on the free particle gyromagnetic ratios. We explain the physical reasons behind this universality.Comment: 10 pp., based on talks given at the Gribov-80 Memorial Workshop, ICTP, Trieste, Italy, May 2010 and at PSAS 2010 workshop, Les Houches, June 2010. To be published in the Gribov-80 Proceedings and in Can. J. Phy

Local gauge invariance implies Siegert's hypothesis

The nonrelativistic Ward-Takahashi identity, a consequence of local gauge invariance in quantum mechanics, shows the necessity of exchange current contributions in case of nonlocal and/or isospin-dependent potentials. It also implies Siegert's hypothesis: in the nonrelativistic limit, two-body charge densities identically vanish. Neither current conservation, which follows from global gauge invariance, nor the constraints of (lowest order) relativity are sufficient to arrive at this result. Furthermore, a low-energy theorem for exchange contributions is established.Comment: 5 pages, REVTE

Quantum projection noise limited interferometry with coherent atoms in a Ramsey type setup

Every measurement of the population in an uncorrelated ensemble of two-level systems is limited by what is known as the quantum projection noise limit. Here, we present quantum projection noise limited performance of a Ramsey type interferometer using freely propagating coherent atoms. The experimental setup is based on an electro-optic modulator in an inherently stable Sagnac interferometer, optically coupling the two interfering atomic states via a two-photon Raman transition. Going beyond the quantum projection noise limit requires the use of reduced quantum uncertainty (squeezed) states. The experiment described demonstrates atom interferometry at the fundamental noise level and allows the observation of possible squeezing effects in an atom laser, potentially leading to improved sensitivity in atom interferometers.Comment: 8 pages, 8 figures, published in Phys. Rev.

Radiative Scalar Meson Decays in the Light-Front Quark Model

We construct a relativistic $^3P_0$ wavefunction for scalar mesons within the framework of light-front quark model(LFQM). This scalar wavefunction is used to perform relativistic calculations of absolute widths for the radiative decay processes$(0^{++})\to\gamma\gamma,(0^{++})\to\phi\gamma$, and $(0^{++})\to\rho\gamma$ which incorporate the effects of glueball-$q\bar{q}$ mixing. The mixed physical states are assumed to be $f_0(1370),f_0(1500)$,and $f_0(1710)$ for which the flavor-glue content is taken from the mixing calculations of other works. Since experimental data for these processes are poor, our results are compared with those of a recent non-relativistic model calculation. We find that while the relativistic corrections introduced by the LFQM reduce the magnitudes of the decay widths by 50-70%, the relative strengths between different decay processes are fairly well preserved. We also calculate decay widths for the processes $\phi\to(0^{++})\gamma$ and (0^{++})\to\gamma\gamm involving the light scalars $f_0(980)$ and $a_0(980)$ to test the simple $q\bar{q}$ model of these mesons. Our results of $q\bar{q}$ model for these processes are not quite consistent with well-established data, further supporting the idea that $f_0(980)$ and $a_0(980)$ are not conventional $q\bar{q}$ states.Comment: 10 pages, 4 figure

Particulate matter pollution in African cities

Abstract: Rapid urban population growth, air pollution emissions, and changing patterns of disease in African cities may increase the burden of air pollution-related morbidity and mortality in coming decades. Yet, air monitoring is limited across the continent and many countries lack air quality standards. This paper focuses on particulate matter (PM) pollution, one of the most relevant and widely used indicators of urban air quality. We provide an overview of published PM monitoring studies in Africa, outline major themes, point out data gaps, and discuss strategies for addressing particulate air pollution in rapidly growing African cities. Our review reveals that, although few studies have reported annual mean levels of coarse and fine particles, collective evidence from short- and long-term air monitoring studies across urban Africa demonstrates that pollution levels often exceed international guidelines. Furthermore, pollution levels may be rising as a result of increased motor vehicle traffic building on already high background concentrations of PM in many locations due to climatic and geographic conditions. Biomass burning and industrial activities, often located in cities, further exacerbate levels of PM. Despite the health risks this situation presents, air quality programs, particularly in sub-Saharan Africa, have been stalled or discontinued in recent years. Implementation of systematic PM data collection would enable air pollution-related health impact assessments, the development of strategies to reduce the air pollution health burden, and facilitate urban planning and transportation policy as it relates to air quality and health. Keywords Urban air quality, Environmental health, Particulate matter, PM10, PM2.5, Afric

Scaling in many-body systems and proton structure function

The observation of scaling in processes in which a weakly interacting probe delivers large momentum ${\bf q}$ to a many-body system simply reflects the dominance of incoherent scattering off target constituents. While a suitably defined scaling function may provide rich information on the internal dynamics of the target, in general its extraction from the measured cross section requires careful consideration of the nature of the interaction driving the scattering process. The analysis of deep inelastic electron-proton scattering in the target rest frame within standard many-body theory naturally leads to the emergence of a scaling function that, unlike the commonly used structure functions $F_1$ and $F_2$, can be directly identified with the intrinsic proton response.Comment: 11 pages, 4 figures. Proceedings of the 11th Conference on Recent Progress in Many-Body Theories, Manchester, UK, July 9-13 200