4,580 research outputs found
Mach's Principle and Model for a Broken Symmetric Theory of Gravity
We investigate spontaneous symmetry breaking in a conformally invariant
gravitational model. In particular, we use a conformally invariant scalar
tensor theory as the vacuum sector of a gravitational model to examine the idea
that gravitational coupling may be the result of a spontaneous symmetry
breaking. In this model matter is taken to be coupled with a metric which is
different but conformally related to the metric appearing explicitly in the
vacuum sector. We show that after the spontaneous symmetry breaking the
resulting theory is consistent with Mach's principle in the sense that inertial
masses of particles have variable configurations in a cosmological context.
Moreover, our analysis allows to construct a mechanism in which the resulting
large vacuum energy density relaxes during evolution of the universe.Comment: 9 pages, no figure
Novel Ï-Extended Quinazoline-Ferrocene Conjugates: Synthesis, Structure, and Redox Behavior
Novel ferrocene conjugates of tricyclic quinazoline derivatives are prepared by condensation of active C-6 methylene groups of mackinazolinones with ferrocenecarbaldehyde. Following this route the conjugated parent alkaloid as well as derivatives with nitro, amino, and alkanoylamino groups at C-2 were attached at the ferrocene moiety, thereby significantly extending the delocalized Ï system. In addition, the parent compound was subjected to the reaction with ferrocene-1,1'-dicarbaldehyde, giving rise to the symmetrical and unsymmetrical double condensation products â 1,1'-disubstituted ferrocene derivatives, which bear two alkaloid substituents. Some of the compounds obtained were subjected to X-ray crystallographic analyses. The influence of the substituents at C-2 through the extended conjugated Ï system on the iron atom is reflected by results of cyclovoltammetric measurements
The Inflationary Brane-Antibrane Universe
We show how the motion through the extra dimensions of a gas of branes and
antibranes can, under certain circumstances, produce an era of inflation as
seen by observers trapped on a 3-brane, with the inflaton being the inter-brane
separation. Although most of our discussion refers to arbitrary p-branes, when
we need to be specific we assume that they are D-branes of Type II or Type I
string theory. For realistic brane couplings, such as those arising in string
theory, the inter-brane potentials are too steep to inflate the universe for
acceptably long times. However, for special regions of the parameter space of
brane-antibrane positions the brane motion is slow enough for there to be
sufficient inflation. Inflation would be more generic in models where the
inter-brane interactions are much weaker. The spectrum of primordial density
fluctuations predicted has index n slightly less than 1, and an acceptable
amplitude, provided that the extra dimensions have linear size 1/r ~ 10^{12}
GeV. Reheating occurs as in hybrid inflation, with the tachyonic instability of
the brane-antibrane system taking over for small separations. The tachyon field
can induce a cascade mechanism within which higher-dimension branes annihilate
into lower-dimension ones. We argue that such a cascade naturally stops with
the production of 3-branes in 10-dimensional string theory.Comment: Final version published in JHE
Management options for restoring estuarine dynamics and implications for ecosystems: a quantitative approach for the Southwest Delta in the Netherlands
The Delta Works, a series of dams and barriers constructed in the 1960'sâ1980's changed the estuarine landscape of the Rhine-Meuse-Scheldt delta (SW Netherlands) into more stagnant and disengaged freshwater, brackish water or saltwater lakes. The remaining tidal systems were adapted by building a storm surge barrier in the Oosterschelde and dike reinforcement works along the Westerschelde. The Delta Works brought protection against flooding, but at the same time resulted in environmental and socio-economic problems, such as degradation of ecological quality and ecosystem functioning, disruption of fish migration routes, water and sediment quality problems.In this study we explore in an integrated, quantitative way the consequences of a number of management options for the Southwest Delta and their implications for the occurrence and distribution of aquatic and estuarine habitats, considering the mutual coherence between the water basins. Five scenarios were evaluated using a 1D hydraulic, water quality and primary production numerical model and GIS habitat mapping. Scenarios vary from small-scale interventions, such as changes in day-to-day management of hydraulic infrastructures or creation of small inlets in dams, feasible in the short term, to restoration of an open delta by removing dams and barriers, as a long term potential. We evaluate the outcomes in relation to the restoration of estuarine dynamics, as this is in policy plans proposed as a generic solution for the current ecological and environmental problems. Net water flow rates show more complex patterns when connectivity between water basins is increased and when sluice management is less strict. Estuarine transition zones and fish migration routes are partly restored, but only fully develop when basins are in open connection with each other. Area of intertidal habitats, tidal flats and tidal marshes, increases in each scenario, ranging between 7 and 83%, 1â56%, and 8â100% respectively, depending on scenario. Large scale infrastructural adaptations are needed to restore estuarine dynamics at large scale.The use of a 1D numerical model allowed to quantify the effect of different management measures for all water basins simultaneously, but also has its limitations. The model does not resolve more complex processes such as vertical mixing and morphodynamic changes. This requires expert judgment and more detailed 3D modelling
Operator Product Expansion for Exclusive Decays: B^+ ->Ds^+ e+e- and B^+ -> Ds^{*+} e+e-
The decays and proceed
through a weak and an electromagnetic interaction. This is a typical ``long
distance'' process, usually difficult to compute systematically. We propose
that over a large fraction of phase space a combination of an operator product
and heavy quark expansions effectively turns this process into one in which the
weak and electromagnetic interactions occur through a local operator. Moreover,
we use heavy quark spin symmetry to relate all the local operators that appear
in leading order of the operator expansion to two basic ones. We use this
operator expansion to estimate the decay rates for .Comment: 4 pages, 1 figure, Latex, published version in PR
New experimental limit on Pauli Exclusion Principle violation by electrons (the VIP experiment)
The Pauli exclusion principle (PEP) represents one of the basic principles of
modern physics and, even if there are no compelling reasons to doubt its
validity, it still spurs a lively debate, because an intuitive, elementary
explanation is still missing, and because of its unique stand among the basic
symmetries of physics. A new limit on the probability that PEP is violated by
electrons was estabilished by the VIP (VIolation of the Pauli exclusion
principle) Collaboration, using the method of searching for PEP forbidden
atomic transitions in copper. The preliminary value, {1/2}\beta^{2} \textless
4.5\times 10^{-28}, represents an improvement of about two orders of magnitude
of the previous limit. The goal of VIP is to push this limit at the level of
.Comment: submitted to Journal of Physics: Conference Series, by the Institute
of Physic
Sphalerons in Two Higgs Doublet Theories
We undertake a comprehensive investigation of the properties of the sphaleron
in electroweak theories with two Higgs doublets. We do this in as
model-independent a way as possible: by exploring the physical parameter space
described by the masses and mixing angles of the Higgs particles. If there is a
large split in the masses of the neutral Higgs particles, there can be several
sphaleron solutions, distinguished by their properties under parity and the
behaviour of the Higgs field at the origin. In general, these solutions appear
in parity conjugate pairs and are not spherically symmetric, although the
departure from spherical symmetry is small. Including CP violation in the Higgs
potential can change the energy of the sphaleron by up to 14 percent for a
given set of Higgs masses, with significant implications for the baryogenesis
bound on the mass of the lightest Higgs
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