1,508 research outputs found
Hyperons in neutron stars and supernova cores
The properties of compact stars and their formation processes depend on many
physical ingredients. The composition and the thermodynamics of the involved
matter is one of them. We will investigate here uniform strongly interacting
matter at densities and temperatures, where potentially other components than
free nucleons appear such as hyperons, mesons or even quarks. In this paper we
will put the emphasis on two aspects of stellar matter with non-nucleonic
degrees of freedom. First, we will study the phase diagram of baryonic matter
with strangeness, showing that the onset of hyperons, as that of quark matter,
could be related to a very rich phase structure with a large density domain
covered by phase coexistence. Second, we will investigate thermal effects on
the equation of state (EoS), showing that they favor the appearance of
non-nucleonic particles. We will finish by reviewing some recent results on the
impact of non-nucleonic degrees freedom in compact star mergers and
core-collapse events, where thermal effects cannot be neglected.Comment: 20 pages, 14 figures, contribution to the EPJA topical issue "Exotic
matter in neutron stars
Hyperons in neutron star matter within relativistic mean-field models
Since the discovery of neutron stars with masses around 2 solar masses the
composition of matter in the central part of these massive stars has been
intensively discussed. Within this paper we will (re)investigate the question
of the appearance of hyperons. To that end we will perform an extensive
parameter study within relativistic mean field models. We will show that it is
possible to obtain high mass neutron stars (i) with a substantial amount of
hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses,
and (iii) a spinodal instability at the onset of hyperons. The results depend
strongly on the interaction in the hyperon-hyperon channels, on which only very
little information is available from terrestrial experiments up to now.Comment: 15 pages, 10 figure
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
On unifying the description of meson and baryon properties
A Poincare' covariant Faddeev equation is presented, which enables the
simultaneous prediction of meson and baryon observables using the leading-order
in a truncation of the Dyson-Schwinger equations that can systematically be
improved. The solution describes a nucleon's dressed-quark core. The evolution
of the nucleon mass with current-quark mass is discussed. A nucleon-photon
current, which can produce nucleon form factors with realistic Q^2-evolution,
is described. Axial-vector diquark correlations lead to a neutron Dirac form
factor that is negative, with r_1^{nu}>r_1^{nd}. The proton electric-magnetic
form factor ratio falls with increasing Q^2.Comment: 5 pages, 4 figures, 1 tabl
Everything Hits at Once: How Remote Rainfall Matters for the Prediction of the 2021 North American Heat Wave
In June 2021, Western North America experienced an intense heat wave with unprecedented temperatures and far-reaching socio-economic consequences. Anomalous rainfall in the West Pacific triggers a cascade of weather events across the Pacific, which build up a high-amplitude ridge over Canada and ultimately lead to the heat wave. We show that the response of the jet stream to diabatically enhanced ascending motion in extratropical cyclones represents a predictability barrier with regard to the heat wave magnitude. Therefore, probabilistic weather forecasts are only able to predict the extremity of the heat wave once the complex cascade of weather events is captured. Our results highlight the key role of the sequence of individual weather events in limiting the predictability of this extreme event. We therefore conclude that it is not sufficient to consider such rare events in isolation but it is essential to account for the whole cascade over different spatiotemporal scales
Portable Vis-NIR und MIR Spektroskopie zur Erfassung von Bodeneigenschaften im Labor und im Gelände: Ergebnisse einer Fallstudie an Lößböden der Querfurter Platte (Sachsen-Anhalt)
Laborbasierte spektroskopische Verfahren im nahen Infrarot (inklusive dem sichtbaren Bereich; Vis-NIR, 400 – 2500 nm) und im mittleren Infrarot (MIR, 2500 – 25000 nm) stellen erprobte Methoden zur quantitativen Erfassung verschiedenster Bodeneigenschaften in Ergänzung zur klassischen Laboranalytik dar. Im MIR-Bereich hat sich als Technik die DRIFT („Diffuse Reflectance Infrared Fourier Transform“)-Spektroskopie etabliert, die, vergleichbar mit der Vis-NIR Spektroskopie, wenig Aufwand bei der Probenaufbereitung erfordert. Im Gegensatz zum Vis-NIR Bereich fehlen im MIR-Bereich Fallstudien mit „in-situ“ Messungen, da portable FTIR-Spektrometer erst seit wenigen Jahren verfügbar sind. Die vorliegende Untersuchung trägt hier zum Lückenschluss bei. Für 100 Ackerstandorte der Querfurter Platte (Tschernoseme der Mitteldeutschen Trockengebiete) wurden mit portablen Vis-NIR und MIR-Geräten (ASD FieldSpec-4 Wide-Res Feldpektroradiometer mit „Contact Probe“; aktives Agilent 4300 Handheld FTIR-Spektrometer mit „Diffuse Reflectance Sample Interface“) in-situ Messungen durchgeführt. Zusätzlich erfolgten eine Probennahme und erneute spektrale Vermessung der aufbereiteten Proben (gemahlen und luftgetrocknet) im Labor; nasschemisch wurden Referenzwerte für den gesamten und den organischen Kohlenstoff, Gesamt-Stickstoffgehalte und ph-Werte ermittelt. Auf dieser Datenbasis werden folgende Fragestellungen behandelt: 1) Vergleich beider Techniken hinsichtlich ihrer Potenziale zur Quantifizierung der genannten Bodengrößen (sowohl im Labor als auch im Gelände) mit verschiedenen multivariaten Kalibrationsansätzen (insbesondere Partial Least Squares Regression mit und ohne Spektralvariablenselektion); 2) Bewertung von Limitationen beider Techniken bei der praktischen Durchführung von Geländemessungen; 3) Möglichkeiten zur synergistischen Nutzung beider Spektralbereiche für eine verbesserte Abschätzung der Bodeneigenschaften
Socioeconomic impact of restless legs syndrome and inadequate restless legs syndrome management across European settings
Restless legs syndrome (RLS) is one of the most common neurological disorders. It describes an irresistible urge to move the legs, mostly manifested in the evening and at night, which can lead to severe sleep disturbance. As part of the European Brain Council (EBC)-led Value-of-Treatment project, this study aimed at capturing the socioeconomic impact of RLS related to the inadequate diagnosis and treatment across different European healthcare settings. The economic burden of RLS was estimated using the published EBC framework of analysis in three separate European Union healthcare systems (France, Germany, and Italy). The RLS care pathway was mapped to identify the unmet needs of patients. Based on specific patient stories, the economic impact of correctly diagnosing RLS and changing between inadequate and target treatment was calculated using appropriate scenario analysis. RLS proved to be a significant personal and social burden, when epidemiological data, high prevalence of RLS, and its need for treatment are combined. By looking at the savings emerging from the provision of optimal care management (timely and correct diagnosis, evidence-based therapy, avoidance of therapy-related complications such as augmentation), the authors foresee substantial economic savings with the achievement of adequate diagnosis and treatment of RLS. Education about RLS is urgently needed for all subspecialties involved in RLS patient care as well as the general public. Equally important, the search for new causal treatment strategies should be intensified to reduce suffering and substantial societal cost
Little Higgs Models and Precision Electroweak Data
We study the low energy limit of Little Higgs models. The method consists in
eliminating the heavy fields using their classical equations of motion in the
infinite mass limit. After the elimination of the heavy degrees of freedom we
can directly read off deviations from the precision electroweak data. We also
examine the effects on the low energy precision experiments.Comment: Misprint in eps3 for the custodial model corrected and additional
discussion of the triplet higg
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