Primordial Power Spectra from Anisotropic Inflation

We examine cosmological perturbations in a dynamical theory of inflation in which an Abelian gauge field couples directly to the inflaton, breaking conformal invariance. When the coupling between the gauge field and the inflaton takes a specific form, inflation becomes anisotropic and anisotropy can persist throughout inflation, avoiding Wald's no-hair theorem. After discussing scenarios in which anisotropy can persist during inflation, we calculate the dominant effects of a small persistent anisotropy on the primordial gravitational wave and curvature perturbation power spectra using the "in-in" formalism of perturbation theory. We find that the primordial power spectra of cosmological perturbations gain significant direction dependence and that the fractional direction dependence of the tensor power spectrum is suppressed in comparison to that of the scalar power spectrum.Comment: 25 pages, 2 figures; References added, typos corrected and some discussion expanded; version submitted for publication in PR

Classical stability of a homogeneous, anisotropic inflating space-time

We study the classical stability of an anisotropic space-time seeded by a spacelike, fixed norm, dynamical vector field in a vacuum-energy-dominated inflationary era. It serves as a model for breaking isotropy during the inflationary era. We find that, for a range of parameters, the linear differential equations for small perturbations about the background do not have a growing mode. We also examine the energy of fluctuations about this background in flat-space. If the kinetic terms for the vector field do not take the form of a field strength tensor squared then there is a negative energy mode and the background is unstable. For the case where the kinetic term is of the form of a field strength tensor squared we show that perturbations about the background have positive energy at lowest order.Comment: 12 pages, no figures; references added, content in section V revised and some clarification made in text; minor typos corrected, v4 closely resembles version published in Phys. Rev. D; in v5 - incorrect argument in section V removed and one reference adde

Sigma-Model Aether

Theories of low-energy Lorentz violation by a fixed-norm "aether" vector field with two-derivative kinetic terms have a globally bounded Hamiltonian and are perturbatively stable only if the vector is timelike and the kinetic term in the action takes the form of a sigma model. Here we investigate the phenomenological properties of this theory. We first consider the propagation of modes in the presence of gravity, and show that there is a unique choice of curvature coupling that leads to a theory without superluminal modes. Experimental constraints on this theory come from a number of sources, and we examine bounds in a two-dimensional parameter space. We then consider the cosmological evolution of the aether, arguing that the vector will naturally evolve to be orthogonal to constant-density hypersurfaces in a Friedmann-Robertson-Walker cosmology. Finally, we examine cosmological evolution in the presence of an extra compact dimension of space, concluding that a vector can maintain a constant projection along the extra dimension in an expanding universe only when the expansion is exponential.Comment: 8 pages, 2 figures; fixed minor typo and changed references in v

Dark Matter, Baryon Asymmetry, and Spontaneous B and L Breaking

We investigate the dark matter and the cosmological baryon asymmetry in a simple theory where baryon (B) and lepton (L) number are local gauge symmetries that are spontaneously broken. In this model, the cold dark matter candidate is the lightest new field with baryon number and its stability is an automatic consequence of the gauge symmetry. Dark matter annihilation is either through a leptophobic gauge boson whose mass must be below a TeV or through the Higgs boson. Since the mass of the leptophobic gauge boson has to be below the TeV scale one finds that in the first scenario there is a lower bound on the elastic cross section of about 5x10^{-46} cm^2. Even though baryon number is gauged and not spontaneously broken until the weak scale, a cosmologically acceptable baryon excess is possible. There is tension between achieving both the measured baryon excess and the dark matter density.Comment: 23 pages, 5 figures; revised version, typos removed, references added, discussion expande

Instabilities in the Aether

We investigate the stability of theories in which Lorentz invariance is spontaneously broken by fixed-norm vector "aether" fields. Models with generic kinetic terms are plagued either by ghosts or by tachyons, and are therefore physically unacceptable. There are precisely three kinetic terms that are not manifestly unstable: a sigma model $(\partial_\mu A_\nu)2$, the Maxwell Lagrangian $F_{\mu\nu}F^{\mu\nu}$, and a scalar Lagrangian $(\partial_\mu A^\mu)2$. The timelike sigma-model case is well-defined and stable when the vector norm is fixed by a constraint; however, when it is determined by minimizing a potential there is necessarily a tachyonic ghost, and therefore an instability. In the Maxwell and scalar cases, the Hamiltonian is unbounded below, but at the level of perturbation theory there are fewer degrees of freedom and the models are stable. However, in these two theories there are obstacles to smooth evolution for certain choices of initial data.Comment: 23 pages, 1 figure; in v2: added references and made minor minor changes to text in sections I and VI; in v3 (version accepted by PRD): added references and made minor changes to discussion in section II

The collective quantization of three-flavored Skyrmions revisited

A self-consistent large $N_c$ approach is developed for the collective quantization of SU(3) flavor hedgehog solitons, such as the Skyrmion. The key to this analysis is the determination of all of the zero modes associated with small fluctuations around the hedgehog. These are used in the conventional way to construct collective coordinates. This approach differs from previous work in that it does not implicitly assume that each static zero mode is associated with a dynamical zero mode. It is demonstrated explicitly in the context of the Skyrmion that there are fewer dynamical zero modes than static ones due to the Witten-Wess-Zumino term in the action. Group-theoretic methods are employed to identify the physical states resulting from canonical quantization of the collectively rotating soliton. The collective states fall into representations of SU(3) flavor labeled by $(p,q)$ and are given by $(2J, \frac{Nc}{2} -J)$ where $J={1/2},{3/2},...$ is the spin of the collective state. States with strangeness $S > 0$ do not arise as collective states from this procedure; thus the $\theta^{+}$ (pentaquark) resonance does not arise as a collective excitation in models of this type.Comment: 12 pages; uses package "youngtab

Chronic dialysis in the infant less than 1 year of age

Dialysis in the infant carries a mortality rate of 16%. Institution of dialysis may be the result of adequate nutritional intake, but avoidance of nutritional intake should never be seen as a way to prevent dialysis. Increased caloric intake, usually via enteral feeding tubes, is needed for optimal growth in the infant with end-stage renal disease (ESRD) in order to attain adequate nutrition with resulting good growth. “Renal” formulae may be constituted as dilute (as in the polyuric infant) or concentrated (as in the anuric infant) to fit the infants needs. Peritoneal dialysis (PD) is the usual mode of renal replacement therapy (97%), with access via a surgically placed cuffed catheter with attention to the placement of the exit site in order to avoid fecal or urinary contamination. PD volumes of 30–40 ml/kg per pass or 800–1,200 ml/m 2 per pass usually result in dialysis adequacy. Additional dietary sodium (3–5 mEq/kg per day) and protein (3–4 g/kg per day) are needed, due to sodium and protein losses in the dialysate. Protein losses are associated with significant infectious morbidity and nonresponsiveness to routine immunizations. Hemodialysis (HD) can be performed either as single- or dual-needle access that have minimal dead space (less then 2 ml) and recirculation rate (less then 5%). Attnetion to extracorporeal blood volume (<10% of intravascular volume), blood flow rates (3–5 ml/kg per min), heparinization (activated clotting times), ultrafiltration (ultrafiltration monitor), and temperature control is imperative during each treatment. Because infants' nutrition is mostly fluid, HD may be needed 4–6 days/week (especially in the oligoanuric infant) to avoid excessive volume overload between treatments. At the end of the treatment a slow blood return with minimal saline rinse is needed to avoid hemodynamic compromise. Infant dialysis, although technically challenging with a significant morbidity and mortality rate, can be safely carried out in the infant with ESRD but requires infant-specific equipment and trained personnel.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47836/1/467_2004_Article_BF00867678.pd

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo