Gravitational Wave Production At The End Of Inflation

We consider gravitational wave production due to parametric resonance at the end of inflation, or ``preheating''. This leads to large inhomogeneities which source a stochastic background of gravitational waves at scales inside the comoving Hubble horizon at the end of inflation. We confirm that the present amplitude of these gravitational waves need not depend on the inflationary energy scale. We analyze an explicit model where the inflationary energy scale is ~10^9 GeV, yielding a signal close to the sensitivity of Advanced LIGO and BBO. This signal highlights the possibility of a new observational ``window'' into inflationary physics, and provides significant motivation for searches for stochastic backgrounds of gravitational waves in the Hz to GHz range, with an amplitude on the order of \Omega_{gw}(k)h^2 ~ 10^-11. Finally, the strategy used in our numerical computations is applicable to the gravitational waves generated by many inhomogeneous processes in the early universe.Comment: 4 pages, Revtex, 2 figures. v2 References added, discussion clarified and improved. v3 further clarification, typo regarding source corrected. Basic results unchange

A New Mechanism for Bubble Nucleation: Classical Transitions

Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic energy can facilitate the classical nucleation of new bubbles in minima that lie below those of the "parent" bubbles. This process is efficient and classical, and changes the dynamics and statistics of bubble formation in models with multiple vacua, relative to that derived from quantum tunneling.Comment: 4 pages, 4 figures, animations related to figures can be found at http://www.perimeterinstitute.ca/personal/jgiblin/BubbleMovies.htm

How to Run Through Walls: Dynamics of Bubble and Soliton Collisions

It has recently been shown in high resolution numerical simulations that relativistic collisions of bubbles in the context of a multi-vacua potential may lead to the creation of bubbles in a new vacuum. In this paper, we show that scalar fields with only potential interactions behave like free fields during high-speed collisions; the kick received by them in a collision can be deduced simply by a linear superposition of the bubble wall profiles. This process is equivalent to the scattering of solitons in 1+1 dimensions. We deduce an expression for the field excursion (shortly after a collision), which is related simply to the field difference between the parent and bubble vacua, i.e. contrary to expectations, the excursion cannot be made arbitrarily large by raising the collision energy. There is however a minimum energy threshold for this excursion to be realized. We verify these predictions using a number of 3+1 and 1+1 numerical simulations. A rich phenomenology follows from these collision induced excursions - they provide a new mechanism for scanning the landscape, they might end/begin inflation, and they might constitute our very own big bang, leaving behind a potentially observable anisotropy.Comment: 15pgs, 14 figures, v2, thanks for the feedback

Association of Diethylstilbestrol Exposure and Uterine Leiomyoma in African American Women

poster abstractUterine leiomyoma, commonly called fibroids, are highly prevalent benign tumors which are leading contributors to hysterectomies. Associated symptoms include reproductive problems, pelvic pain and heavy menstrual bleeding. Fibroids have an elevated occurrence in African American women, along with increased symptom severity and earlier onset among younger age groups. It has been established that hormones influence fibroid development, and recent studies suggest that fibroid development is influenced by fetal and childhood exposures to hormones which later impact how a woman’s body responds to hormonal challenges as an adult. Early life exposure to diethylstilbestrol (DES), which is a teratogenic synthetic estrogen, has been found to cause fibroids in laboratory rodent models. The purpose of this research is to investigate how the mechanisms of DES exposure contribute to disparities in fibroid development in African American women. Coupled with the established role of inheritance in fibroid development, this project hypothesizes that there will be a strong correlation between fetal exposure to DES and the prevalence and severity of fibroids in African American women. The impact of this research will have direct relevance as it can offer insight into preventative medical care by reducing the inheritability of the disease, offer alternative treatment methods and reduce existing health disparities

Molecular Gas in the Powerful Radio Galaxies 3C~31 and 3C~264: Major or Minor Mergers?

We report the detection of $^{12}$CO~($1 \to 0$) and $^{12}$CO~($2 \to 1$) emission from the central regions ($\lesssim 5$--$10 {\rm kpc}$) of the two powerful radio galaxies 3C~31 and 3C~264. Their individual CO emission exhibits a double-horned line profile that is characteristic of an inclined rotating disk with a central depression at the rising part of its rotation curve. The inferred disk or ring distributions of the molecular gas is consistent with the observed presence of dust disks or rings detected optically in the cores of both galaxies. For a CO to H$_2$ conversion factor similar to that of our Galaxy, the corresponding total mass in molecular hydrogen gas is $(1.3 \pm 0.2) \times 10^9 {\rm M_{\odot}}$ in 3C~31 and $(0.31 \pm 0.06) \times 10^9 {\rm M_{\odot}}$ in 3C~264. Despite their relatively large molecular-gas masses and other peculiarities, both 3C~31 and 3C~264, as well as many other powerful radio galaxies in the (revised) 3C catalog, are known to lie within the fundamental plane of normal elliptical galaxies. We reason that if their gas originates from the mergers of two gas-rich disk galaxies, as has been invoked to explain the molecular gas in other radio galaxies, then both 3C~31 and 3C~264 must have merged a long time (a few billion years or more) ago but their remnant elliptical galaxies only recently (last tens of millions of years or less) become active in radio. Instead, we argue that the cannibalism of gas-rich galaxies provides a simpler explanation for the origin of molecular gas in the elliptical hosts of radio galaxies. Given the transient nature of their observed disturbances, these galaxies probably become active in radio soon after the accretion event when sufficient molecular gas agglomerates in their nuclei.Comment: 16 pages, 1 JPEG figure attached, accepted for publication in ApJ

High On/Off Ratio Graphene Nanoconstriction Field Effect Transistor

We report a method to pattern monolayer graphene nanoconstriction field effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET fabrication is enabled by the use of feedback controlled electromigration (FCE) to form a constriction in a gold etch mask that is first patterned using conventional lithographic techniques. The use of FCE allows the etch mask to be patterned on size scales below the limit of conventional nanolithography. We observe the opening of a confinement-induced energy gap as the NCFET width is reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off ratios we obtain with this procedure can be larger than 1000 at room temperature for the narrowest devices; this is the first report of such large room temperature on/off ratios for patterned graphene FETs.Comment: 18 pages, 6 figures, to appear in Smal

Discovery of Radio Emission from the Tight M8 Binary: LP 349-25

We present radio observations of 8 ultracool dwarfs with a narrow spectral type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8 binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system detected in radio and its trigonometric parallax pi = 67.6 mas, recently measured by Gatewood et al., makes it the furthest ultracool system detected by the Very Large Array to date, and the most radio-luminous outside of obvious flaring activity or variability. With a separation of only 1.8 AU, masses of the components of LP 349-25 can be measured precisely without any theoretical assumptions (Forveille et al.), allowing us to clarify their fully-convective status and hence the kind of magnetic dynamo in these components which may play an important role to explain our detection of radio emission from these objects. This also makes LP 349-25 an excellent target for further studies with better constraints on the correlations between X-ray, radio emission and stellar parameters such as mass, age, temperature, and luminosity in ultracool dwarfs.Comment: accepted by ApJ, referee's comments included, typo in equation 1 correcte