The Synthetic-Oversampling Method: Using Photometric Colors to Discover Extremely Metal-Poor Stars

Extremely metal-poor (EMP) stars ([Fe/H] < -3.0 dex) provide a unique window into understanding the first generation of stars and early chemical enrichment of the Universe. EMP stars are exceptionally rare, however, and the relatively small number of confirmed discoveries limits our ability to exploit these near-field probes of the first ~500 Myr after the Big Bang. Here, a new method to photometrically estimate [Fe/H] from only broadband photometric colors is presented. I show that the method, which utilizes machine-learning algorithms and a training set of ~170,000 stars with spectroscopically measured [Fe/H], produces a typical scatter of ~0.29 dex. This performance is similar to what is achievable via low-resolution spectroscopy, and outperforms other photometric techniques, while also being more general. I further show that a slight alteration to the model, wherein synthetic EMP stars are added to the training set, yields the robust identification of EMP candidates. In particular, this synthetic-oversampling method recovers ~20% of the EMP stars in the training set, at a precision of ~0.05. Furthermore, ~65% of the false positives from the model are very metal-poor stars ([Fe/H] < -2.0 dex). The synthetic-oversampling method is biased towards the discovery of warm (~F-type) stars, a consequence of the targeting bias from the SDSS/SEGUE survey. This EMP selection method represents a significant improvement over alternative broadband optical selection techniques. The models are applied to >12 million stars, with an expected yield of ~600 new EMP stars, which promises to open new avenues for exploring the early universe.Comment: 15 pages, 7 figures, to be submitted to Ap

Proton Polarizability Contribution: Muonic Hydrogen Lamb Shift and Elastic Scattering

The uncertainty in the contribution to the Lamb shift in muonic hydrogen, $\Delta E^{subt}$ arising from proton polarizability effects in the two-photon exchange diagram at large virtual photon momenta is shown large enough to account for the proton radius puzzle. This is because $\Delta E^{subt}$ is determined by an integrand that falls very slowly with very large virtual photon momenta. We evaluate the necessary integral using a set of chosen form factors and also a dimensional regularization procedure which makes explicit the need for a low energy constant. The consequences of our two-photon exchange interaction for low-energy elastic lepton-proton scattering are evaluated and could be observable in a planned low energy lepton-proton scattering experiment planned to run at PSI.Comment: 12 pages, two figures. This resubmission is made to handle a problem with the function $\bar{T}_1(0,Q^2)$ pointed out by A. Walker-Loud and Paz \& Hil

The CMB - Contemporary Measurements and Cosmology

Since the discovery of the Cosmic Microwave Background (CMB) in 1965, characterization of the CMB anisotropy angular power spectrum has become somewhat of a holy grail for experimental cosmology. Because CMB anisotropy measurements are difficult, the full potential of the CMB is only now being realized. Improvements in experimental techniques and detector technology have yielded an explosion of progress in the past couple of years resulting in the ability to use measurements of the CMB to place meaningful constraints on cosmological parameters. In this review, I discuss the theory behind the CMB but focus primarily on the experiments, reviewing briefly the history of CMB anisotropy measurements and focusing on the recent experiments that have revolutionized this field. Results from these modern experiments are reviewed and the cosmological implications discussed. I conclude with brief comments about the future of CMB physics.Comment: 18 pages including 5 ps figures. GR16 proceedings to appear in World Scientifi

Infinite Nuclear Matter on the Light Front: A Modern Approach to Brueckner Theory

Understanding an important class of experiments requires that light-front dynamics and related light cone variables k^+ and k_perp be used. If one uses k^+ as a momentum variable, the corresponding canonical spatial variable is x^-=x^0-x^3 and the time variable is x^0+x^3. This is the light front (LF) approach of Dirac. A relativistic light front formulation of nuclear dynamics is developed and applied to treating infinite nuclear matter in a method which includes the corelations of pairs of nculeons. This is light front Brueckner theory.Comment: 7 pages, text of an invited talk presented at the 10th International Conference on Recent Progress In Many-Body Theories. To be published by World Scientific as volume 3 of "Series on Advances in Quantum Many-Body Theory", eds. R.F. Bishop, C.E. Campbell, J.W. Clark and S. Fanton

Using GPS as a reference frame for SAR images applied to a post eruptive period for Okmok Volcano, Aleutian Islands, Alaska

While high spatial coverage makes InSAR a popular tool to study active volcanoes its use can possess challenges for certain environments. Volcanoes along Alaska's Aleutian chain are difficult targets for InSAR as their seasonal snow cover causes decorrelation close to the volcanic caldera, their exposed location in the North Pacific renders them prone to severe atmospheric phase artifacts, and their location on small islands prevents the selection of suitable reference points necessary for deformation analysis. Existing GPS networks define a known reference frame in which SAR is better understood. Okmok volcano is one of the most active volcanoes in the Aleutian Island Chain and shows significant non-linear deformation behavior as it progresses through its eruption cycles. A stack of L-band imagery acquired by the SAR sensor PALSAR on board the JAXA Advanced Land Observing Satellite produced a post eruption deformation time series between August 2008 and October 2010. This data along with a merged DEM comprised of AirSAR SRTM and Worldview-1 stereo pair data, and GPS data from 3 continuous and 3 post eruption campaign sites was used for this study. In this research, a comparison and combination of InSAR and GPS time-series data will be presented aimed at the following research goals: 1) What is the accuracy and precision of InSAR-derived deformation estimates in such challenging environments; 2) How accurate can the deformation of the InSAR reference point be estimated from a joint analysis of InSAR and GPS deformation signals; 3) How non-linear volcanic deformation can be constrained by the measurements of a local GPS network and support the identification of residual atmospheric signals in InSAR-derived deformation time series. Further research into the combination of GPS and InSAR applied to the nonlinear aspect of volcanic deformation can enhance geodetic modeling of the volcano and associated eruption processes