Maximum Entropy Estimation of the Galactic Bulge Morphology via the VVV Red Clump

The abundance and narrow magnitude dispersion of Red Clump (RC) stars make them a popular candidate for mapping the morphology of the bulge region of the Milky Way. Using an estimate of the RC's intrinsic luminosity function, we extracted the three-dimensional density distribution of the RC from deep photometric catalogues of the VISTA Variables in the Via Lactea (VVV) survey. We used maximum entropy based deconvolution to extract the spatial distribution of the bulge from Ks-band star counts. We obtained our extrapolated non-parametric model of the bulge over the inner 40 by 40 degrees squared region of the Galactic centre. Our reconstruction also naturally matches onto a parametric fit to the bulge outside the VVV region and inpaints overcrowded and high extinction regions. We found a range of bulge properties consistent with other recent investigations based on the VVV data. In particular, we estimated the bulge mass to be in the range 13 to 17 billion solar masses, the X-component to be between 18% and 25% of the bulge mass, and the bulge angle with respect to the Sun-Galactic centre line to be between 18 and 32 degrees. Studies of the Fermi Large Area Telescope (LAT) gamma-ray Galactic centre excess suggests that the excess may be traced by Galactic bulge distributed sources. We applied our deconvolved density in a template fitting analysis of this Fermi-LAT GeV excess and found an improvement in the fit compared to previous parametric based templates.Comment: 25 pages, 27 figures, minor typo correcte

Non-Parametric Density Reconstruction of the Galactic Bulge Area using Red Clump Stars in the VVV Survey

Studies of the red clump giant population in the inner Milky Way suggest the Galactic bulge/bar has a boxy/peanut/X-shaped structure as predicted by its formation via a disc buckling instability. We used a non-parametric method of estimating the Galactic bulge morphology that is based on maximum entropy regularisation. This enabled us to extract the three-dimensional distribution of the red giant stars in the bulge from deep photometric catalogues of the VISTA Variables in the Via Lactea (VVV) survey. Our high-resolution reconstruction confirms the well-known boxy/peanut/X-shaped structure of the bulge. We also find spiral arm structures that extend to around three kpc in front of and behind the bulge and are on different sides of the bulge major axis. We show that the detection of these structures is robust to the uncertainties in the luminosity function.Comment: 12 pages, 8 figures, V4: MNRAS accepted versio

Tristability in a non-equilibrium double-quantum-dot in Kondo regime

Electron tunneling through a non-equilibrium double quantum dot in the Kondo regime is studied. In the region of negative differential resistance, it is shown that this system possesses a complex response to the applied potential characterized by a tristable solution for the current. Increasing the applied potential or reducing the inter-dot coupling, the system goes through a transition from a coherent inter-dot regime to an incoherent one. The different nature of the solutions are characterized and it is shown that the effects of the asymmetry in the dot-lead coupling can be used to control the region of multistability. The mean-field slave-boson formalism is used to obtain the solution of the problem.Comment: 4 pages, 4 figures. To appear in Sol. State. Com

An Approach to the Cosmological Constant Problem(s)

We propose an approach to explaining why naive large quantum fluctuations are not the right estimate for the cosmological constant. We argue that the universe is in a superposition of many vacua, in such a way that the resulting fluctuations are suppressed by level repulsion to a very small value. The approach combines several aspects of string theory and the early history of the universe, and is only valid if several assumptions hold true. The approach may also explain why the effective cosmological constant reamins small as the universe evolves though several phase transitions. It provides a non-anthropic mechansim leading to a small, non-zero cosmological constant.Comment: Talk given at Rencontres de Moriond, 2004 by G.L. Kan

Structure and transport in multi-orbital Kondo systems

We consider Kondo impurity systems with multiple local orbitals, such as rare earth ions in a metallic host or multi--level quantum dots coupled to metallic leads. It is shown that the multiplet structure of the local orbitals leads to multiple Kondo peaks above the Fermi energy $E_F$, and to ``shadow'' peaks below $E_F$. We use a slave boson mean field theory, which recovers the strong coupling Fermi liquid fixed point, to calculate the Kondo peak positions, widths, and heights analytically at T=0, and NCA calculations to fit the temperature dependence of high--resolution photoemission spectra of Ce compounds. In addition, an approximate conductance quantization for transport through multi--level quantum dots or single--atom transistors in the Kondo regime due to a generalized Friedel sum rule is demonstrated.Comment: 4 pages, 3 figures. Invited article, 23rd International Conference on Low Temperature Physics LT23, Hiroshima, Japan 200

Geographical variation in cancer survival in England, 1991–2006: an analysis by Cancer Network

BACKGROUND: Reducing geographical inequalities in cancer survival in England was a key aim of the Calman-Hine Report (1995) and the NHS Cancer Plan (2000). This study assesses whether geographical inequalities changed following these policy developments by analysing the trend in 1-year relative survival in the 28 cancer networks of England. METHODS: Population-based age-standardised relative survival at 1 year is estimated for 1.4 million patients diagnosed with cancer of the oesophagus, stomach, colon, lung, breast (women) or cervix in England during 1991-2006 and followed up to 2007. Regional and deprivation-specific life tables are built to adjust survival estimates for differences in background mortality. Analysis is divided into three calendar periods: 1991-5, 1996-2000 and 2001-6. Funnel plots are used to assess geographical variation in survival over time. RESULTS: One-year relative survival improved for all cancers except cervical cancer. There was a wide geographical variation in survival with generally lower estimates in northern England. This north-south divide became less marked over time, although the overall number of cancer networks that were lower outliers compared with the England value remained stable. Breast cancer was the only cancer for which there was a marked reduction in geographical inequality in survival over time. CONCLUSION: Policy changes over the past two decades coincided with improved relative survival, without an increase in geographical variation. The north-south divide in relative survival became less pronounced over time but geographical inequalities persist. The reduction in geographical inequality in breast cancer survival may be followed by a similar trend for other cancers, provided government recommendations are implemented similarly

Kondo effect in side coupled double quantum-dot molecule

Electron tunneling through a double quantum dot molecule side attached to a quantum wire, in the Kondo regime, is studied. The mean-field finite-U slave-boson formalism is used to obtain the solution of the problem. We found conductance cancelations when the molecular energies of the side attached double quantum-dot cross the Fermi energy. We investigate the many body molecular Kondo states as a function of the parameters of the system.Comment: 12 pages, 7 figures. Submitted to Solid State Com

Bayesian High-Redshift Quasar Classification from Optical and Mid-IR Photometry

We identify 885,503 type 1 quasar candidates to i<22 using the combination of optical and mid-IR photometry. Optical photometry is taken from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III/BOSS), while mid-IR photometry comes from a combination of data from the Wide-Field Infrared Survey Explorer (WISE) "ALLWISE" data release and several large-area Spitzer Space Telescope fields. Selection is based on a Bayesian kernel density algorithm with a training sample of 157,701 spectroscopically-confirmed type-1 quasars with both optical and mid-IR data. Of the quasar candidates, 733,713 lack spectroscopic confirmation (and 305,623 are objects that we have not previously classified as photometric quasar candidates). These candidates include 7874 objects targeted as high probability potential quasars with 3.5<z<5 (of which 6779 are new photometric candidates). Our algorithm is more complete to z>3.5 than the traditional mid-IR selection "wedges" and to 2.2<z<3.5 quasars than the SDSS-III/BOSS project. Number counts and luminosity function analysis suggests that the resulting catalog is relatively complete to known quasars and is identifying new high-z quasars at z>3. This catalog paves the way for luminosity-dependent clustering investigations of large numbers of faint, high-redshift quasars and for further machine learning quasar selection using Spitzer and WISE data combined with other large-area optical imaging surveys.Comment: 54 pages, 17 figures; accepted by ApJS Data for tables 1 and 2 available at http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/master_quasar_catalogs.011414.fits.bz2 and http://www.physics.drexel.edu/~gtr/outgoing/optirqsos/data/optical_ir_quasar_candidates.052015.fits.bz

On the perturbative expansion of the magnetization in the out-of-equilibrium Kondo model

This paper is concerned with the out-of-equilibrium two-lead Kondo model, considered as a model of a quantum dot in the Kondo regime. We revisit the perturbative expansion of the dot's magnetization, and conclude that, even at order 0 in the Kondo interactions, the magnetization is not given by the usual equilibrium result. We use the Schwinger-Keldysh method to derive a Dyson equation describing the steady state induced by the voltage between the two leads, and thus present the correct procedure for calculating perturbative expansions of steady-state properties of the system.Comment: Minor corrections forgotten in v