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Charge-parity (CP) asymmetries in charm decays are extremely suppressed in the Standard Model and may well be dominated by new-physics contributions. The LHCb collaboration reported the results of direct CP asymmetry measurements in $D^0\to K^+ K^-$ and $D^0\to \pi^+\pi^-$ decays with unprecedented accuracy: $a_{\rm{CP}}(K^+ K^-)=(7.7\pm5.7)\times 10^{-4}$ and $a_{\rm{CP}}(\pi^+\pi^-)=(23.2\pm6.1)\times 10^{-4}$, with the latter quantity inferred from the precise measurement of $\Delta a_{\rm{CP}} =\, a_{\rm{CP}}(K^+ K^-) -a_{\rm{CP}}(\pi^+\pi^-) =\, (-15.7\pm2.9)\times 10^{-4}$. When interpreted within the Standard Model, these values indicate a breakdown of the approximate $U$-spin symmetry of QCD. If, however, this symmetry holds and the data stem from new physics, other CP asymmetries should be enhanced as well. We derive CP asymmetry sum rules based on $\rm{SU}(3)$ flavor symmetry for $D$ meson decays into a pair of pseudoscalar mesons as well as a pair of a pseudoscalar and a vector meson for two generic scenarios, with $\Delta U=0$ and $|\Delta U|=1$ interactions, respectively. The correlations implied by the sum rules can be used to check the consistency between different measurements and to discriminate between these scenarios with future data. For instance, we find $a_{\mathrm{CP}}(\pi^{+}K^{* 0}) + a_{\mathrm{CP}}(K^{+}\overline{K}^{* 0}) = 0$ for $\Delta U=0$ new physics and the opposite relative sign for the $|\Delta U|=1$ case. One sum rule, connecting four decay modes, holds in both scenarios. We further extend our sum rules to certain differences of CP asymmetries from which the $D$ production asymmetries drop out., Comment: 11 pages, 1 figure, 4 tables

We have modeled the diffuse background at the Galactic Poles in the far-ultraviolet (FUV: 1536 \AA) and the near-ultraviolet (NUV: 2316 \AA). The background is well-fit using a single-scattering dust model with an offset representing the extragalactic light plus any other contribution to the diffuse background. We have found a dust albedo of 0.35 -- 0.40 (FUV) and 0.11 -- 0.19 in the NGP ($b > 70^{\circ}$) and 0.46 -- 0.56 (FUV) and 0.31 -- 0.33 (NUV) in the SGP ($b < 70^{\circ}$. The differences in the albedo may reflect changes in the dust-to-gas ratio over the sky or in the dust distribution. We find offsets at zero-reddening of 273 -- 286 and 553 -- 581 photons cm$^{-2}$ s$^{-1}$ sr$^{-1}$ \AA$^{-1}$ in the FUV and NUV, respectively, in the NGP with similar values in the SGP., Comment: 5 pages, 7 figures, Accepted in Journal of Astronomy and Astrophysics

Einstein's happiest thought was his leap from the observation that a falling person feels no gravity to the realization that gravity might be equivalent to acceleration. It affects all bodies in the same way because it is a property of spacetime -- its curvature -- not a force propagating through spacetime (like electromagnetic or nuclear forces). When expressed in a way that is manifestly independent of the choice of coordinates, this idea became General Relativity. But the ground for what is now known as the "equivalence principle" was laid long before Einstein, affording a fascinating example of the growth of a scientific idea through the continuous interplay between theory and experiment. That story continues through the present era, with improved techniques and measurements, and in the new environment of space. Theoretically, equivalence is now understood to rank with Lorentz invariance as one of nature's most fundamental principles. Violations of equivalence are generically predicted by attempts to unify gravity with "non-geometrical" fundamental interactions, but there is no consensus on the form that these violations will take. Experimental tests of equivalence thus face the challenge of striving simultaneously for the highest possible sensitivity and diversity in test materials., Comment: 20 pages, 4 figures; http://www.minkowskiinstitute.com/MIM/Equivalence.pdf

We report on preliminary results of a statistical study of student performance in more than a decade of calculus-based introductory physics courses. Treating average homework and test grades as proxies for student effort and comprehension respectively, we plot comprehension versus effort in an academic version of the astronomical Hertzsprung-Russell diagram (which plots stellar luminosity versus temperature). We study the evolution of this diagram with time, finding that the "academic main sequence" has begun to break down in recent years as student achievement on tests has become decoupled from homework grades. We present evidence that this breakdown is likely related to the emergence of easily accessible online solutions to most textbook problems, and discuss possible responses and strategies for maintaining and enhancing student learning in the online era.

Pythagoras' theorem lies at the heart of physics as well as mathematics, yet its historical origins are obscure. We highlight a purely pictorial, gestalt-like proof that may have originated during the Zhou Dynasty. Generalizations of the Pythagorean theorem to three, four and more dimensions undergird fundamental laws including the energy-momentum relation of particle physics and the field equations of general relativity, and may hint at future unified theories. The "pre-mathematical" nature of this theorem lends support to the Eddingtonian view that "the stuff of the world is mind-stuff.", Comment: To appear in the inaugural issue of Minkowski Institute Magazine

We have used Voyager and Galex observations to map the diffuse Galactic light near the Galactic equator. We find that most of the observations are relatively faint with surface brightnesses of less than 5,000 photon units. This is important because many ultraviolet telescopes have not observed at low Galactic latitudes because of the fear of a bright diffuse emission. Our data are consistent with emission from interstellar dust grains with albedo ($a$) of 0.2 -- 0.3 and phase function ($g$) $ < 0.7$ at 1100 \AA; $0.2 < a < 0.5; g < 0.8$ at 1500 \AA; and $0.4 < a < 0.6; g < 0.4$ at 2300 \AA., Comment: Submitted to MNRAS

We have used data from the Galaxy Evolution Explorer to study the different components of the diffuse ultraviolet background in the region between the Galactic latitudes 70-80 degree. We find an offset at zero dust column density (E(B - V) = 0) of $240 \pm 18$ photon units in the FUV (1539A) and $394 \pm 37$ photon units in the NUV (2316A). This is approximately half of the total observed radiation with the remainder divided between an extragalactic component of $114 \pm 18$ photon units in the FUV and $194 \pm 37$ photon units in the NUV and starlight scattered by Galactic dust at high latitudes. The optical constants of the dust grains were found to be a=0.4$\pm$0.1 and g=0.8$\pm$0.1 (FUV) and a=0.4$\pm$0.1 and g=0.5$\pm$0.1 (NUV). We cannot differentiate between a Galactic or extragalactic origin for the zero-offset but can affirm that it is not from any known source., Comment: Accepted for publication in MNRAS 7 pages, 6 figures

A short scientific biography is given of physicist Paul Wesson (1949-2015), who published over 300 works encompassing the fields of astrobiology, astrophysics, geophysics, cosmology, and relativity; and who was particularly associated with a fully covariant version of Kaluza-Klein theory known as Space-Time-Matter theory, in which matter and energy in four dimensions are induced from empty space in higher dimensions, thus realizing Einstein's dream and unifying the gravitational field with its source., Comment: Appendix from a forthcoming book by P.S. Wesson and J.M. Overduin, Principles of Space-Time-Matter: Cosmology, Particles and Waves in Five Dimensions (Singapore: World Scientific, 2018); https://www.worldscientific.com/worldscibooks/10.1142/10871

We draw attention to observational evidence indicating that a substantial fraction of the well-known cosmic celestial diffuse ultraviolet background radiation field is actually due not to dust-scattered starlight, but rather---considering its spectral character at most locations in the sky---has an unknown physical origin. We arrive at this conclusion from re-examination of spectra of the diffuse ultraviolet background that were obtained---long ago---using the ultraviolet spectrometers aboard the two Voyager spacecraft, which were located far out in our solar system, and at very different locations. As there is neither a reasonable nor even an unreasonable conventional astrophysical source for this newly-identified fraction of the radiation, we are led to speculate that the photons that we observe have their origin in the very slow decay of the particles that make up the ubiquitous dark matter, which we know envelopes our Galaxy. Whether or not that actually is the source, this new radiation field extends somewhat below 912 {\AA}, so we have found, at last, the radiation that re-ionized the universe.

We have used GALEX observations of the North and South Galactic poles to study the diffuse ultraviolet background at locations where the Galactic light is expected to be at a minimum. We find offsets of 230 -- 290 photon units in the FUV (1531 \AA) and 480 -- 580 photon units in the NUV (2361 \AA). Of this, approximately 120 photon units can be ascribed to dust scattered light and another 110 (190 in the NUV) photon units to extragalactic radiation. The remaining radiation is, as yet, unidentified and amounts to $120 -- 180$ photon units in the FUV and $300 -- 400$ photon units in the NUV. We find that molecular hydrogen fluorescence contributes to the FUV when the 100 $\mu$m surface brightness is greater than 1.08 MJy sr$^{-1}$., Comment: 11 pages and 13 figures

The proposed Satellite Test of the Equivalence Principle (STEP) will detect possible violations of the Weak Equivalence Principle by measuring relative accelerations between test masses of different composition with a precision of one part in $10^{18}$. A serendipitous byproduct of the experimental design is that the absolute (common-mode) acceleration of the test masses is also measured to high precision as they oscillate along a common axis under the influence of restoring forces produced by the position sensor currents, which in drag-free mode lead to Newtonian accelerations as small as $10^{-14}$ g. This is deep inside the low-acceleration regime where Modified Newtonian Dynamics (MOND) diverges strongly from the Newtonian limit of General Relativity. We show that MOND theories (including those based on the widely-used $n$-family of interpolating functions as well as the covariant Tensor-Vector-Scalar formulation) predict an easily detectable increase in the frequency of oscillations of the STEP test masses if the Strong Equivalence Principle holds. If it does not hold, MOND predicts a cumulative increase in oscillation amplitude which is also detectable. STEP thus provides a new and potentially decisive test of Newton's law of inertia, as well as the equivalence principle in both its strong and weak forms., Comment: 5 pages, 3 figures; in press at Physical Review Letters

We use experimental limits on Lorentz violation to obtain new constraints on Kaluza-Klein-type theories in which the extra dimensions may be large but do not necessarily have units of length. The associated variation in fundamental quantities such as rest mass must occur slowly, on cosmological scales., Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016

Black holes are real astrophysical objects, but their interiors are hidden and can only be "observed" through mathematics. The structure of rotating black holes is typically illustrated with the help of special coordinates. But any such coordinate choice necessarily results in a distorted view, just as the choice of projection distorts a map of the Earth. The truest way to depict the properties of a black hole is through quantities that are coordinate-invariant. We compute and plot all the independent curvature invariants of rotating, charged black holes for the first time, revealing a landscape that is much more beautiful and complex than usually thought., Comment: 4 pages, 3 figures, published in Bridges Baltimore 2015: Mathematics, Music, Art, Architecture, Culture (Phoenix, AZ: Tessellations Publishing, 2015), 479-482. Revised to fix a reference

We use observational data on the magnitude-redshift relation for Type Ia supernovae together with constraints on the ages of the oldest stars to rule out a higher-dimensional extension of General Relativity with a negative kinetic-energy scalar field. This theory is of considerable physical interest because it produces accelerated expansion at both early and late times with a single new field, as in quintessential inflation scenarios. It is also of mathematical interest because it is characterized by an analytic expression for the macroscopic scale factor $a(t)$. We show that cosmological solutions of this theory can be usefully parametrized by a single quantity, the lookback time $\tau_{\text{tr}}$ corresponding to the transition from deceleration to acceleration. Supernovae data from the recently released Supernova Cosmology Project Union 2.1 compilation single out a narrow range of values for $\tau_{\text{tr}}$. In the context of the theory, however, these same values of $\tau_{\text{tr}}$ imply that the universe is much older than the oldest observed stars., Comment: 10 pages, 5 figures

We give a new, wave-like solution of the field equations of five-dimensional relativity. In ordinary three-dimensional space, the waves resemble de Broglie or matter waves, whose puzzling behaviour can be better understood in terms of one or more extra dimensions. Causality is appropriately defined by a null higher-dimensional interval. It may be possible to test the properties of these waves in the laboratory., Comment: 15 pages, no figures

It is more important than ever to push experimental tests of gravitational theory to the limits of existing technology in both range and sensitivity. This brief review focuses on spin-based tests of General Relativity and their implications for alternative, mostly non-metric theories of gravity motivated by the challenge of unification with the Standard Model of particle physics. The successful detection of geodetic precession and frame-dragging by Gravity Probe B places new constraints on a number of these theories, and increases our confidence in the theoretical mechanisms underpinning current ideas in astrophysics and cosmology., Comment: To appear in a special issue of Classical and Quantum Gravity devoted to the GP-B experiment. 13 pages, 1 figure