Spectroscopy of Seven Cataclysmic Variables with Periods Above Five Hours

We present spectroscopy of seven cataclysmic variable stars with orbital periods P(orb) greater than 5 hours, all but one of which are known to be dwarf novae. Using radial velocity measurements we improve on previous orbital period determinations, or derive periods for the first time. The stars and their periods are TT Crt, 0.2683522(5) d; EZ Del, 0.2234(5) d; LL Lyr, 0.249069(4) d; UY Pup, 0.479269(7) d; RY Ser, 0.3009(4) d; CH UMa, 0.3431843(6) d; and SDSS J081321+452809, 0.2890(4) d. For each of the systems we detect the spectrum of the secondary star, estimate its spectral type, and derive a distance based on the surface brightness and Roche lobe constraints. In five systems we also measure the radial velocity curve of the secondary star, estimate orbital inclinations, and where possible estimate distances based on the MV(max) vs.P(orb) relation found by Warner. In concordance with previous studies, we find that all the secondary stars have, to varying degrees, cooler spectral types than would be expected if they were on the main sequence at the measured orbital period.Comment: 25 pages, 2 figures, accepted for Publications of the Astronomical Society of the Pacifi

From Newton's Laws to the Wheeler-DeWitt Equation

This is a pedagogical paper which explains some ideas in cosmology at a level accessible to undergraduate students. It does not use general relativity, but uses the ideas of Newtonian cosmology worked out by Milne and McCrea. The cosmological constant is also introduced within a Newtonian framework. Following standard quantization procedures the Wheeler-DeWitt equation in the minisuperspace approximation is derived for empty and non-empty universes.Comment: 13 pages, 1 figur

SnapLink: Fast and Accurate Vision-Based Appliance Control in Large Commercial Buildings

As the number and heterogeneity of appliances in smart buildings increases, identifying and controlling them becomes challenging. Existing methods face various challenges when deployed in large commercial buildings. For example, voice command assistants require users to memorize many control commands. Attaching Bluetooth dongles or QR codes to appliances introduces considerable deployment overhead. In comparison, identifying an appliance by simply pointing a smartphone camera at it and controlling the appliance using a graphical overlay interface is more intuitive. We introduce SnapLink, a responsive and accurate vision-based system for mobile appliance identification and interaction using image localization. Compared to the image retrieval approaches used in previous vision-based appliance control systems, SnapLink exploits 3D models to improve identification accuracy and reduce deployment overhead via quick video captures and a simplified labeling process. We also introduce a feature sub-sampling mechanism to achieve low latency at the scale of a commercial building. To evaluate SnapLink, we collected training videos from 39 rooms to represent the scale of a modern commercial building. It achieves a 94% successful appliance identification rate among 1526 test images of 179 appliances within 120 ms average server processing time. Furthermore, we show that SnapLink is robust to viewing angle and distance differences, illumination changes, as well as daily changes in the environment. We believe the SnapLink use case is not limited to appliance control: it has the potential to enable various new smart building applications.</jats:p

Parallax and Distance Estimates for Fourteen Cataclysmic Variable Stars

I used the 2.4 m Hiltner telescope at MDM Observatory in an attempt to measure trigonometric parallaxes for 14 cataclysmic variable stars. Techniques are described in detail. In the best cases the parallax uncertainties are below 1 mas, and significant parallaxes are found for most of the program stars. A Bayesian method which combines the parallaxes together with proper motions and absolute magnitude constraints is developed and used to derive distance estimates and confidence intervals. The most precise distance derived here is for WZ Sge, for which I find 43.3 (+1.6, -1.5) pc. Six Luyten Half-Second stars with previous precise parallax measurements were re-measured to test the techniques, and good agreement is found.Comment: 33 pages, 3 figures. Astronomical Journal, accepte

Evidence for electronically-driven ferroelectricity in the family of strongly correlated dimerized BEDT-TTF molecular conductors

By applying measurements of the dielectric constants and relative length changes to the dimerized molecular conductor $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl, we provide evidence for order-disorder type electronic ferroelectricity which is driven by charge order within the (BEDT-TTF)$_2$ dimers and stabilized by a coupling to the anions. According to our density functional theory calculations, this material is characterized by a moderate strength of dimerization. This system thus bridges the gap between strongly dimerized materials, often approximated as dimer-Mott systems at 1/2 filling, and non- or weakly dimerized systems at 1/4 filling exhibiting charge order. Our results indicate that intra-dimer charge degrees of freedom are of particular importance in correlated $\kappa$-(BEDT-TTF)$_2$X salts and can create novel states, such as electronically-driven multiferroicity or charge-order-induced quasi-1D spin liquids.Comment: 6 pages, 4 figures + Supplementary Information (8 pages, 8 figures

Natural Candidates for Superheavy Dark Matter in String and M Theory

We reconsider superheavy dark matter candidates in string and M theory, in view of the possibility that inflation might generate superheavy particles with an abundance close to that required for a near-critical Universe. We argue that cryptons - stable or metastable bound states of matter in the hidden sector - are favoured over other possible candidates in string or $M$ theory, such as the Kaluza-Klein states associated with extra dimensions. We exhibit a specific string model that predicts cryptons as hidden-sector bound states weighing $\sim 10^{12}$ GeV, and discuss their astrophysical observability.Comment: 4 pages, revtex, no figur

Enhanced signal of astrophysical tau neutrinos propagating through Earth

Earth absorbs \nue and \numu of energies above about 100 TeV. As is well-known, although \nutau will also disappear through charged-current interactions, the \nutau flux will be regenerated by prompt tau decays. We show that this process also produces relatively large fluxes of secondary \nube and \nubmu, greatly enhancing the detectability of the initial \nutau. This is particularly important because at these energies \nutau is a significant fraction of the expected astrophysical neutrino flux, and only a tiny portion of the atmospheric neutrino flux.Comment: Four pages, two inline figure

Baryon number non-conservation and phase transitions at preheating

Certain inflation models undergo pre-heating, in which inflaton oscillations can drive parametric resonance instabilities. We discuss several phenomena stemming from such instabilities, especially in weak-scale models; generically, these involve energizing a resonant system so that it can evade tunneling by crossing barriers classically. One possibility is a spontaneous change of phase from a lower-energy vacuum state to one of higher energy, as exemplified by an asymmetric double-well potential with different masses in each well. If the lower well is in resonance with oscillations of the potential, a system can be driven resonantly to the upper well and stay there (except for tunneling) if the upper well is not resonant. Another example occurs in hybrid inflation models where the Higgs field is resonant; the Higgs oscillations can be transferred to electroweak (EW) gauge potentials, leading to rapid transitions over sphaleron barriers and consequent B+L violation. Given an appropriate CP-violating seed, we find that preheating can drive a time-varying condensate of Chern-Simons number over large spatial scales; this condensate evolves by oscillation as well as decay into modes with shorter spatial gradients, eventually ending up as a condensate of sphalerons. We study these examples numerically and to some extent analytically. The emphasis in the present paper is on the generic mechanisms, and not on specific preheating models; these will be discussed in a later paper.Comment: 10 pages, 7 figures included, revtex, epsf, references adde

Reheating Temperature and Inflaton Mass Bounds from Thermalization After Inflation

We consider the conditions for the decay products of perturbative inflaton decay to thermalize. The importance of considering the full spectrum of inflaton decay products in the thermalization process is emphasized. It is shown that the delay between the end of inflaton decay and thermalization allows the thermal gravitino upper bound on the reheating temperature to be raised from 10^{8} GeV to as much as 10^{12} GeV in realistic inflation models. Requiring that thermalization occurs before nucleosynthesis imposes an upper bound on the inflaton mass as a function of the reheating temperature, m_{S} < 10^{10} (T_{R}/1 GeV)^{7/9} GeV. It is also shown that even in realistic inflation models with relatively large reheating temperatures, it is non-trivial to have thermalization before the electroweak phase transition temperature. Therefore the thermal history of the Universe is very sensitive to details of the inflation model.Comment: 12 Pages LaTeX. Catalysed thermalization discussion correcte