16,523 research outputs found
Comment on "Scalar-tensor gravity coupled to a global monopole and flat rotation curves" by Lee and Lee
The recent paper by Lee and Lee (2004) may strongly leave the impression that
astronomers have established that the rotation curves of spiral galaxies are
flat. We show that the old paradigm of Flat Rotation Curves lacks, today, any
observational support and following it at face value leads to intrinsically
flawed alternatives to the Standard Dark Matter Scenario. On the other side, we
claim that the rich systematics of spiral galaxy rotation curves, that reveals,
in the standard Newtonian Gravity framework, the phenomenon of dark matter, in
alternative scenarios, works as a unique benchmark.Comment: 3 pages, 2 figures, accepted in Phys. Rev.
Higgs-Flavor Groups, Naturalness, and Dark Matter
In the absence of low-energy supersymmetry, a multiplicity of weak-scale
Higgs doublets would require additional fine-tunings unless they formed an
irreducible multiplet of a non-abelian symmetry. Remnants of such symmetry
typically render some Higgs fields stable, giving several dark matter particles
of various masses. The non-abelian symmetry also typically gives simple,
testable mass relations.Comment: Some comments added after Eqs. (2) and (12
On the Creation of the Universe out of Nothing
We explain how the Universe was created with no expenditure of energy or
initial mass.Comment: To be presented at IWARA 2009 (4th International Workshop on
Astronomy and Relativistic Astrophysics), to be held in Brazil, October 200
The resultant parameters of effective theory
This is the 4-th paper in the series devoted to a systematic study of the
problem of mathematically correct formulation of the rules needed to manage an
effective field theory. Here we consider the problem of constructing the full
set of essential parameters in the case of the most general effective
scattering theory containing no massless particles with spin J > 1/2. We
perform the detailed classification of combinations of the Hamiltonian coupling
constants and select those which appear in the expressions for renormalized
S-matrix elements at a given loop order.Comment: 21 pages, 4 LaTeX figures, submitted to Phys. Rev.
NVV auger spectra from W(100)
The NVV Auger spectrum from a clean W(100) surface has been measured in the second derivative, d^2N (E)/dE^2, mode to enhance fine structure. This measurement is compared with spectra generated from both the self‐convolution of the tungsten valence‐band bulk density of states (obtained from a relativistic APW energy band calculation) and a "restricted convolution" in which only transitions involving electrons from the same valence energy are allowed. The restricted convolution for a model of the Auger process in which both N_6VV and N_7VV transitions contribute offers the best match of theory and experiment. No distinct evidence of Auger emission involving the surface resonance present on W(100) is observed. Effects of H_2 and O_2 adsorption on the Auger spectrum of the W(100) surface are reported
The gravitational analogue to the hydrogen atom (A summer study at the borders of quantum mechanics and general relativity)
This article reports on a student summer project performed in 2006 at the
University of Frankfurt. It is addressed to undergraduate students familiar
with the basic principles of relativistic quantum mechanics and general
relativity. The aim of the project was to study the Dirac equation in curved
space time. To obtain the general relativistic Dirac equation we use the
formulation of gravity as a gauge theory in the first part. After these general
considerations we restrict the further discussion to the special case of the
Schwarzschild metric. This setting corresponds to the hydrogen atom, with the
electromagnetic field replaced by gravity. Although there is a singularity at
the event horizon it turns out that a regular solution of the time independent
Dirac equation exists. Finally the Dirac equation is solved numerically using
suitable boundary conditions.Comment: 19 pages, 3 figure
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
Line element in quantum gravity: the examples of DSR and noncommutative geometry
We question the notion of line element in some quantum spaces that are
expected to play a role in quantum gravity, namely non-commutative deformations
of Minkowski spaces. We recall how the implementation of the Leibniz rule
forbids to see some of the infinitesimal deformed Poincare transformations as
good candidates for Noether symmetries. Then we recall the more fundamental
view on the line element proposed in noncommutative geometry, and re-interprete
at this light some previous results on Connes' distance formula.Comment: some references added. Proceedings of the Second Workshop on Quantum
Gravity and Noncommutative Geometry, Universidade Lusofona, Lisbon 22-24
September 200
A response to arXiv:1310.2791: A self-consistent public catalogue of voids and superclusters in the SDSS Data Release 7 galaxy surveys
Recently, Nadathur & Hotchkiss (2013) submitted a paper discussing a new
cosmic void catalog. This paper includes claims about the void catalog
described in Sutter et al. (2012). In this note, we respond to those claims,
clarify some discrepancies between the text of Sutter et al. (2012) and the
most recent version of the catalog, and provide some comments on the
differences between our catalog and that of Nadathur & Hotchkiss (2013). All
updates and documentation for our catalog are available at
http://www.cosmicvoids.net.Comment: 3 pages, 1 figure, public catalog available at
http://www.cosmicvoids.ne
Constraints and Hamiltonian in Light-Front Quantized Field Theory
Self-consistent Hamiltonian formulation of scalar theory on the null plane is
constructed following Dirac method. The theory contains also {\it constraint
equations}. They would give, if solved, to a nonlinear and nonlocal
Hamiltonian. The constraints lead us in the continuum to a different
description of spontaneous symmetry breaking since, the symmetry generators now
annihilate the vacuum. In two examples where the procedure lacks
self-consistency, the corresponding theories are known ill-defined from
equal-time quantization. This lends support to the method adopted where both
the background field and the fluctuation above it are treated as dynamical
variables on the null plane. We let the self-consistency of the Dirac procedure
determine their properties in the quantized theory. The results following from
the continuum and the discretized formulations in the infinite volume limit do
agree.Comment: 11 pages, Padova University preprint DFPF/92/TH/52 (December '92
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