The Paths of Quintessence

The structure of the dark energy equation of state phase plane holds important information on the nature of the physics. We explain the bounds of the freezing and thawing models of scalar field dark energy in terms of the tension between the steepness of the potential vs. the Hubble drag. Additionally, we extend the phase plane structure to modified gravity theories, examine trajectories of models with certain properties, and categorize regions in terms of scalar field hierarchical parameters, showing that dark energy is generically not a slow roll phenomenon.Comment: 12 pages, 7 figures; matches PRD versio

Slow nucleation rates in Chain Inflation with QCD Axions or Monodromy

The previous proposal (by two of us) of chain inflation with the QCD axion is shown to fail. The proposal involved a series of fast tunneling events, yet here it is shown that tunneling is too slow. We calculate the bubble nucleation rates for phase transitions in the thick wall limit, approximating the barrier by a triangle. A similar problem arises in realization of chain inflation in the string landscape that uses series of minima along the monodromy staircase around the conifold point. The basic problem is that the minima of the potential are too far apart to allow rapid enough tunneling in these two models. We entertain the possibility of overcoming this problem by modifying the gravity sector to a Brans-Dicke theory. However, one would need extremely small values for the Brans-Dicke parameter. Many successful alternatives exist, including other "axions" (with mass scales not set by QCD) or potentials with comparable heights and widths that do not suffer from the problem of slow tunneling and provide successful candidates for chain inflation.Comment: 6 pages, 1 figur

Chain Inflation in the Landscape: "Bubble Bubble Toil and Trouble"

In the model of Chain Inflation, a sequential chain of coupled scalar fields drives inflation. We consider a multidimensional potential with a large number of bowls, or local minima, separated by energy barriers: inflation takes place as the system tunnels from the highest energy bowl to another bowl of lower energy, and so on until it reaches the zero energy ground state. Such a scenario can be motivated by the many vacua in the stringy landscape, and our model can apply to other multidimensional potentials. The ''graceful exit'' problem of Old Inflation is resolved since reheating is easily achieved at each stage. Coupling between the fields is crucial to the scenario. The model is quite generic and succeeds for natural couplings and parameters. Chain inflation succeeds for a wide variety of energy scales -- for potentials ranging from 10MeV scale inflation to $10^{16}$ GeV scale inflation.Comment: 31 pages, 3 figures, one reference adde

Cascade events at IceCube + DeepCore as a definitive constraint on the dark matter interpretation of the PAMELA and Fermi anomalies

Dark matter decaying or annihilating into μ^+μ^- or τ^+τ^- has been proposed as an explanation for the e^± anomalies reported by PAMELA and Fermi. Recent analyses show that IceCube, supplemented by DeepCore, will be able to significantly constrain the parameter space of decays to μ^+μ^-, and rule out decays to τ^+τ^- and annihilations to μ^+μ^- in less than five years of running. These analyses rely on measuring tracklike events in IceCube + DeepCore from down-going ν_μ. In this paper we show that by instead measuring cascade events, which are induced by all neutrino flavors, IceCube + DeepCore can rule out decays to μ^+μ^- in only three years of running, and rule out decays to τ^+τ^- and annihilation to μ^+μ^- in only one year of running. These constraints are highly robust to the choice of dark matter halo profile and independent of dark matter-nucleon crosssection

Correspondence from E.B. Lovejoy, June 28, 1862

Correspondence from E.B. Lovejoy regarding absent soldiers from Androscoggin Countyhttps://digitalmaine.com/absent_soldiers/1002/thumbnail.jp

Effects of vertical vibration on hopper flows of granular material

The discharge of granular material from a hopper subject to vertical sinusoidal oscillations was investigated using experiments and discrete element computer simulations. With the hopper exit closed, side-wall convection cells are observed, oriented such that particles move up along the inclined walls of the hopper and down at the center line. The convection cells are a result of the granular bed dilation during free fall and the subsequent interaction with the hopper walls. The mass discharge rate for a vibrating hopper scaled by the discharge rate without vibration reaches a maximum value at a dimensionless velocity amplitude just greater than 1. Further increases in the velocity decrease the discharge rate. The decrease occurs due to a decrease in the bulk density of the discharging material when vibration is applied

The Vascular Flora of Clay Prairie State Preserve (Butler County, Iowa): Recommendations to the Iowa State Preserve System

Clay Prairie State Preserve (1.2 ha) is an upland prairie located in Butler County, IA, and represents one of the last remnants of black-soil tallgrass prairie in northeast Iowa. An annotated checklist of the vascular flora of Clay Prairie is presented here, based on a previously published flora of the preserve and recent field work conducted by the authors between 1997 to 2001, and 2008 to 2011. The preserve contains a diverse vascular flora representing 50 families, 145 genera and 214 taxa (174 native to Iowa). In comparison with 26 larger prairies (4 to 121 ha) protected in the Iowa state preserves system, the Clay Prairie flora ranks 10th in total number of native Iowa prairie plant taxa (135 taxa) and 10th in total number of native Iowa prairie plant taxa assigned high (7 to 10) values of the Iowa Conservation Coefficient (55 taxa). As a remnant of formerly much more extensive tallgrass prairie in Iowa, Clay Prairie protects individual plant taxa, plant assemblages, and ecological and evolutionary processes, while providing opportunities for people to experience native prairie. The floristic comparisons presented in this paper suggest that the floras of many other prairies protected in the Iowa State Preserves system are not thoroughly documented. Hence, we recommend that floristic studies of these other prairie preserves be undertaken to include documentation of the entire flora by voucher specimens. We also encourage site managers of prairies in the Iowa State Preserves system to prepare annual reports summarizing management and educational activities that occur in these preserves