A5061242206- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Relativity and Gravitational Theory
- Quantum Mechanics and Applications
- Dark Matter and Cosmic Phenomena
- Noncommutative and Quantum Gravity Theories
- Space Science and Extraterrestrial Life
- Galaxies: Formation, Evolution, Phenomena
- Reconstructive Surgery and Microvascular Techniques
- Earth Systems and Cosmic Evolution
- Particle physics theoretical and experimental studies
- Advanced Thermodynamics and Statistical Mechanics
- Astronomy and Astrophysical Research
- Orthopedic Surgery and Rehabilitation
- Stellar, planetary, and galactic studies
- Microbial Metabolic Engineering and Bioproduction
- History and Developments in Astronomy
- Philosophy and History of Science
- Surgical Simulation and Training
- Monoclonal and Polyclonal Antibodies Research
- Computational Physics and Python Applications
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Diversity and Career in Medicine
- Digital Imaging in Medicine
California Institute of Technology
2014-2023
Johns Hopkins University
2022-2023
St. Vincent's University Hospital
2006-2022
Royal College of Surgeons in Ireland
2008-2022
Santa Fe Institute
2021
Itasca Consultants (United States)
2017-2020
James A. Haley Veterans' Hospital
2020
Axcella Health (United States)
2016-2019
Creative Commons
2017
Harvard University
1994-2017
We show that cosmic acceleration can arise due to very tiny corrections the usual gravitational action of general relativity, form ${R}^{\ensuremath{-}n}$ with $n>0.$ This model eliminates need for a nonzero cosmological constant or any other dark energy, attributing purely origin universe.
The cosmological constant problem is examined in the context of both astronomy and physics. Effects a nonzero are discussed with reference to expansion dynamics, age universe, distance measures, comoving density objects, growth linear perturbations, gravitational lens probabilities. observational status reviewed, attention given existence high-redshift derivation from globular clusters cosmic nuclear data, dynamical tests Omega sub Lambda, quasar absorption line statistics, lensing,...
The Chern-Simons Lagrangian has been studied previously in (2+1)-dimensional spacetime, where it is both gauge and Lorentz invariant. In 3+1 dimensions, this term couples the dual electromagnetic tensor to an external four-vector. If we take four-vector be fixed, invariant but not paper, examine theoretical consequences of such a modification observational limits can put on its magnitude. would rotate plane polarization radiation from distant galaxies, effect which observed. From...
Models of dark energy are conveniently characterized by the equation-of-state parameter $w=p/\ensuremath{\rho},$ where $\ensuremath{\rho}$ is density and p pressure. Imposing dominant condition, which guarantees stability theory, implies that $w>~\ensuremath{-}1.$ Nevertheless, it conceivable a well-defined model could (perhaps temporarily) have $w<\ensuremath{-}1 ,$ indeed such models been proposed. We study dynamical exhibiting $w<\ensuremath{-}1$ virtue negative kinetic term. Although...
A nearly massless, slowly rolling scalar field $\ensuremath{\varphi}$ may provide most of the energy density current Universe. One potential difficulty with this idea is that couplings to ordinary matter should lead observable long-range forces and time dependence constants nature. I explore possibility an approximate global symmetry serves suppress such even further. Such a would allow coupling pseudoscalar ${F}_{\ensuremath{\mu}\ensuremath{\nu}}{\stackrel{\ifmmode \tilde{}\else...
The role of Lorentz symmetry in noncommutative field theory is considered. Any realistic found to be physically equivalent a subset general Lorentz-violating standard-model extension involving ordinary fields. Some theoretical consequences are discussed. Existing experiments bound the scale noncommutativity parameter $(10\mathrm{TeV}{)}^{\ensuremath{-}2}$.
We use Type Ia supernovae studied by the High-z Supernova Search Team to constrain properties of an energy component that may have contributed accelerating cosmic expansion. find for a flat geometry equation-of-state parameter unknown component, αx = Px/ρx, must be less than -0.55 (95% confidence) any value Ωm, and it is further limited < -0.60 if Ωm assumed greater 0.1. These values are inconsistent with being topological defects such as domain walls, strings, or textures. The supernova...
According to Darwinian theory, complexity evolves by a stepwise process of elaboration and optimization under natural selection. Biological systems composed tightly integrated parts seem challenge this view, because it is not obvious how any element's function can be selected for unless the partners with which interacts are already present. Here we demonstrate an molecular system-the specific functional interaction between steroid hormone aldosterone its partner mineralocorticoid...
We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions extremely low space-time curvature. investigate far future evolution universe such models, examining possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution exhibit interesting set attractor solutions which, some cases, provide alternatives to dark energy models.
These notes represent approximately one semester's worth of lectures on introductory general relativity for beginning graduate students in physics. Topics include manifolds, Riemannian geometry, Einstein's equations, and three applications: gravitational radiation, black holes, cosmology.
We explore the feasibility and astrophysical consequences of a new long-range $U(1)$ gauge field (``dark electromagnetism'') that couples only to dark matter, not standard model. The matter consists an equal number positive negative charges under force, but annihilations are suppressed if dark-matter mass is sufficiently high fine-structure constant $\stackrel{^}{\ensuremath{\alpha}}$ small. correct relic abundance can be obtained also conventional weak interactions, we verify this...
Rotational invariance is a well-established feature of low-energy physics. Violations this symmetry must be extremely small today, but could have been larger in earlier epochs. In paper we examine the consequences breaking rotational during inflationary era when primordial density fluctuations were generated. Assuming that fixed-norm vector picked out preferred-direction era, explore imprint it would leave on cosmic microwave background anisotropy, and provide explicit formulas for expected...
Despite its highly inflammatory nature, LPS is a molecule with remarkable therapeutic potential. Lipid A glycolipid that serves as the hydrophobic anchor of and constitutes potent ligand Toll-like receptor (TLR)4/myeloid differentiation factor 2 innate immune system. less toxic mixture monophosphorylated lipid species (MPL) recently became first new Food Drug Administration-approved adjuvant in over 70 y. Whereas wild-type Escherichia coli provokes strong MyD88 (myeloid primary response gene...
We examine how to construct a spatial manifold and its geometry from the entanglement structure of an abstract quantum state in Hilbert space. Given decomposition space $\mathcal{H}$ into tensor product factors, we consider class ``redundancy-constrained states'' that generalize area-law behavior for entropy usually found condensed-matter systems with gapped local Hamiltonians. Using mutual information define distance measure on graph, employ classical multidimensional scaling extract...
We consider the gravitational effects of a single, fixed-norm, Lorentz-violating timelike vector field. In cosmological background, such field acts to rescale effective value Newton's constant. The energy density this precisely tracks rest universe, but with opposite sign, so that universe experiences slower rate expansion for given matter content. This similarly rescales constant in Newtonian limit, although by different factor. put constraints on parameters theory using predictions...
The existence of large-scale magnetic fields in galaxies is well established, but there no accepted mechanism for generating a primordial field which could grow into what observed today. We discuss model attempts to account the necessary by invoking pseudo-Goldstone boson coupled electromagnetism. evolution this during inflation generates field; however, it seems difficult on rather general grounds obtain sufficient strength astrophysically interesting scales.
Measurements of CMB temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that fluctuation amplitude in one half sky differs from other half. We show such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to homogeneity Universe. In contrast, a multi-field inflationary theory, curvaton model, can produce this power constraint. The mechanism requires introduction large-amplitude superhorizon perturbation...
Significance Almost all biological systems need to respond multiple simultaneous inputs. In yeast catabolite repression, a textbook model for signaling integration, the preferred carbohydrate glucose is thought inhibit induction of galactose genes when above threshold concentration. Instead, we show that metabolic depends on ratio and glucose. Surprisingly, critical portion information processing determines response occurs upstream canonical pathway. The use modern combinatorial approaches...