37 research outputs found
Dynamical vacuum selection in field theories with flat directions in their potential
In this paper we show that in field theories with topologically stable kinks
and flat directions in their potential, a so-called dynamical vacuum selection
(DVS) takes place in the non-trivial, soliton sector of the theory. We explore
this DVS mechanism using a specific model. For this model we show that there is
only a static kink solution when very specific boundary conditions are met,
very similar to the case of vortices in two dimensions. In the case of other
boundary conditions a scalar cloud is expelled to infinity, leaving a static
kink behind. Other circumstances under which DVS may or may not take place are
discussed as well.Comment: 10 pages, 6 figure
More on core instabilities of magnetic monopoles
In this paper we present new results on the core instability of the 't Hooft
Polyakov monopoles we reported on before. This instability, where the spherical
core decays in a toroidal one, typically occurs in models in which charge
conjugation is gauged. In this paper we also discuss a third conceivable
configuration denoted as ``split core'', which brings us to some details of the
numerical methods we employed. We argue that a core instability of 't Hooft
Polyakov type monopoles is quite a generic feature of models with charged Higgs
particles.Comment: Latex, 15 pages, 6 figures; published versio
Anyons in discrete gauge theories with Chern-Simons terms
We study the effect of a Chern-Simons term in a theory with discrete gauge
group H, which in (2+1)-dimensional space time describes (non-abelian) anyons.
As in a previous paper, we emphasize the underlying algebraic structure, namely
the Hopf algebra D(H). We argue on physical grounds that the addition of a
Chern-Simons term in the action leads to a non-trivial 3-cocycle on D(H).
Accordingly, the physically inequivalent models are labelled by the elements of
the cohomology group H^3(H,U(1)). It depends periodically on the coefficient of
the Chern-Simons term which model is realized. This establishes a relation with
the discrete topological field theories of Dijkgraaf and Witten. Some
representative examples are worked out explicitly.Comment: 18 page
Quantumgroups in the Higgs Phase
In the Higgs phase we may be left with a residual finite symmetry group H of
the condensate. The topological interactions between the magnetic- and electric
excitations in these so-called discrete H gauge theories are completely
described by the Hopf algebra or quantumgroup D(H). In 2+1 dimensional space
time we may add a Chern-Simons term to such a model. This deforms the
underlying Hopf algebra D(H) into a quasi-Hopf algebra by means of a 3-cocycle
H. Consequently, the finite number of physically inequivalent discrete H gauge
theories obtained in this way are labelled by the elements of the cohomology
group H^3(H,U(1)). We briefly review the above results in these notes. Special
attention is given to the Coulomb screening mechanism operational in the Higgs
phase. This mechanism screens the Coulomb interactions, but not the
Aharonov-Bohm interactions. (Invited talk given by Mark de Wild Propitius at
`The III International Conference on Mathematical Physics, String Theory and
Quantum Gravity', Alushta, Ukraine, June 13-24, 1993. To be published in Theor.
Math. Phys.)Comment: 19 pages in Latex, ITFA-93-3
Dead time effect on the Brewer measurements: correction and estimated uncertainties
Brewer spectrophotometers are widely used instruments which perform spectral measurements of the direct, the scattered and the global solar UV irradiance. By processing these measurements a variety of secondary products can be derived such as the total columns of ozone (TOC), sulfur dioxide and nitrogen dioxide and aerosol optical properties. Estimating and limiting the uncertainties of the final products is of critical importance. High-quality data have a lot of applications and can provide accurate estimations of trends
Decay of Metastable Topological Defects
We systematically analyze the decay of metastable topological defects that
arise from the spontaneous breakdown of gauge or global symmetries.
Quantum-mechanical tunneling rates are estimated for a variety of decay
processes. The decay rate for a global string, vortex, domain wall, or kink is
typically suppressed compared to the decay rate for its gauged counterpart. We
also discuss the decay of global texture, and of semilocal and electroweak
strings.Comment: 43 pages, harvmac, HUTP-92/A018, CALT-68-178
Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV¿visible spectrometers during CINDI-2
40 pags., 22 figs., 13 tabs.In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17¿d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97¿¿N, 4.93¿¿E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation.
The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions.
The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.CINDI-2 received funding from the Netherlands Space Office (NSO). Funding for this study was provided
by ESA through the CINDI-2 (ESA contract no. 4000118533/16/ISbo) and FRM4DOAS (ESA contract no. 4000118181/16/I-EF)
projects and partly within the EU 7th Framework Programme
QA4ECV project (grant agreement no. 607405). The BOKU
MAX-DOAS instrument was funded and the participation of Stefan F. Schreier was supported by the Austrian Science Fund
(FWF): I 2296-N29. The participation of the University of Toronto
team was supported by the Canadian Space Agency (through
the AVATARS project) and the Natural Sciences and Engineering Research Council (through the PAHA project). The instrument was primarily funded by the Canada Foundation for Innovation and is usually operated at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network
for the Detection of Atmospheric Change (CANDAC). Funding for
CISC was provided by the UVAS (“Ultraviolet and Visible Atmospheric Sounder”) projects SEOSAT/INGENIO, ESP2015-71299-
R, MINECO-FEDER and UE. The activities of the IUP-Heidelberg
were supported by the DFG project RAPSODI (grant no. PL
193/17-1). SAOZ and Mini-SAOZ instruments are supported by the
Centre National de la Recherche Scientifique (CNRS) and the Centre National d’Etudes Spatiales (CNES). INTA recognises support
from the National funding projects HELADO (CTM2013-41311-P) and AVATAR (CGL2014-55230-R). AMOIAP recognises support from the Russian Science Foundation (grant no. 16-17-10275) and the Russian Foundation for Basic Research (grant nos. 16-05-
01062 and 18-35-00682). Ka L. Chan received transnational access funding from ACTRIS-2 (H2020 grant agreement no. 654109).
Rainer Volkamer recognises funding from NASA’s Atmospheric Composition Program (NASA-16-NUP2016-0001) and the US National Science Foundation (award AGS-1620530). Henning Finkenzeller is the recipient of a NASA graduate fellowship. Mihalis Vrekoussis recognises support from the University of Bremen and the DFG Research Center/Cluster of Excellence “The Ocean in the
Earth System-MARUM”. Financial support through the University of Bremen Institutional Strategy in the framework of the
DFG Excellence Initiative is gratefully appreciated for Anja Schönhardt. Pandora instrument deployment was supported by Luftblick
through the ESA Pandonia Project and NASA Pandora Project at the Goddard Space Flight Center under NASA Headquarters’ Tropospheric Composition Program. The article processing charges for
this open-access publication were covered by BK Scientific