7,902 research outputs found
Kondo effect in a one dimensional d-wave superconductor
We derive a solvable resonant-level type model, to describe an impurity spin
coupled to zero-energy bound states localized at the edge of a one dimensional
d-wave superconductor. This results in a two-channel Kondo effect with a quite
unusual low-temperature thermodynamics. For instance, the local impurity
susceptibility yields a finite maximum at zero temperature (but no
logarithmic-divergence) due to the splitting of the impurity in two Majorana
fermions. Moreover, we make comparisons with the Kondo effect occurring in a
two dimensional d-wave superconductor.Comment: 9 pages, final version; To be published in Europhysics Letter
Black Hole Lightning from the Peculiar Gamma-Ray Loud Active Galactic Nucleus IC 310
The nearby active galaxy IC 310, located in the outskirts of the Perseus
cluster of galaxies is a bright and variable multi-wavelength emitter from the
radio regime up to very high gamma-ray energies above 100 GeV. Originally, the
nucleus of IC 310 has been classified as a radio galaxy. However, studies of
the multi-wavelength emission showed several properties similarly to those
found from blazars as well as radio galaxies. In late 2012, we have organized
the first contemporaneous multi-wavelength campaign including radio, optical,
X-ray and gamma-ray instruments. During this campaign an exceptionally bright
flare of IC 310 was detected with the MAGIC telescopes in November 2012
reaching an averaged flux level in the night of up to one Crab above 1 TeV with
a hard spectrum over two decades in energy. The intra-night light curve showed
a series of strong outbursts with flux-doubling time scales as fast as a few
minutes. The fast variability constrains the size of the gamma-ray emission
regime to be smaller than 20% of the gravitational radius of its central black
hole. This challenges the shock acceleration models, commonly used to explain
gamma-ray radiation from active galaxies. Here, we will present more details on
the MAGIC data and discuss several possible alternative emission models.Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray
Conference, 30 July - 6 August, 2015, The Hague, The Netherland
Insights into the particle acceleration of a peculiar gamma -ray radio galaxy IC 310
IC 310 has recently been identified as a gamma-ray emitter based on
observations at GeV energies with Fermi-LAT and at very high energies (VHE, E >
100 GeV) with the MAGIC telescopes. Despite IC 310 having been classified as a
radio galaxy with the jet observed at an angle > 10 degrees, it exhibits a
mixture of multiwavelength properties of a radio galaxy and a blazar, possibly
making it a transitional object. On the night of 12/13th of November 2012 the
MAGIC telescopes observed a series of violent outbursts from the direction of
IC 310 with flux-doubling time scales faster than 5 min and a peculiar spectrum
spreading over 2 orders of magnitude. Such fast variability constrains the size
of the emission region to be smaller than 20% of the gravitational radius of
its central black hole, challenging the shock acceleration models, commonly
used in explanation of gamma-ray radiation from active galaxies. Here we will
show that this emission can be associated with pulsar-like particle
acceleration by the electric field across a magnetospheric gap at the base of
the jet.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Regularization of 2d supersymmetric Yang-Mills theory via non commutative geometry
The non commutative geometry is a possible framework to regularize Quantum
Field Theory in a nonperturbative way. This idea is an extension of the lattice
approximation by non commutativity that allows to preserve symmetries. The
supersymmetric version is also studied and more precisely in the case of the
Schwinger model on supersphere [14]. This paper is a generalization of this
latter work to more general gauge groups
Review of Results from the NA49 Collaboration
New results of the NA49 collaboration on strange particle production are
presented. Rapidity and transverse mass spectra as well as total multiplicities
are discussed. The study of their evolution from AGS over SPS to the highest
RHIC energy reveals a couple of interesting features. These include a sudden
change in the energy dependence of the mt-spectra and of the yields of strange
hadrons around 30 AGeV. Both are found to be difficult to be reproduced in a
hadronic scenario, but might be an indication for a phase transition to a quark
gluon plasma.Comment: 8 pages, 7 figures. Proceedings of the SQM04 conference, Capetow
A generation apart? Youth and political participation in Britain
Conventional wisdom holds that young people in Britain are alienated from politics, with some claiming that this reflects a wider crisis of legitimacy that should be met by initiatives to increase citizenship. This article addresses these areas, presenting both panel survey and focus group data from first-time voters. It concludes that, contrary to the findings from many predominantly quantitative studies of political participation, young people are interested in political matters, and do support the democratic process. However they feel a sense of anti-climax having voted for the first time, and are critical of those who have been elected to positions of political power. If they are a generation apart, this is less to do with apathy, and more to do with their engaged scepticism about ‘formal’ politics in Britain
Making the most of community energies:Three perspectives on grassroots innovation
Grassroots innovations for sustainability are attracting increasing policy attention. Drawing upon a wide range of empirical research into community energy in the UK, and taking recent support from national government as a case study, we apply three distinct analytical perspectives: strategic niche management; niche policy advocacy; and critical niches. Whilst the first and second perspectives appear to explain policy influence in grassroots innovation adequately, each also shuts out more transformational possibilities. We therefore argue that, if grassroots innovation is to realise its full potential, then we need to also pursue a third, critical niches perspective, and open up debate about more socially transformative pathways to sustainability
Evolution of emission line activity in intermediate mass young stars
We present optical spectra of 45 intermediate mass Herbig Ae/Be stars.
Together with the multi-epoch spectroscopic and photometric data compiled for a
large sample of these stars and ages estimated for individual stars by using
pre-main sequence evolutionary tracks, we have studied the evolution of
emission line activity in them. We find that, on average, the H_alpha emission
line strength decreases with increasing stellar age in HAeBe stars, indicating
that the accretion activity gradually declines during the PMS phase. This would
hint at a relatively long-lived (a few Myr) process being responsible for the
cessation of accretion in Herbig Ae/Be stars. We also find that the accretion
activity in these stars drops substantially by ~ 3 Myr. This is comparable to
the timescale in which most intermediate mass stars are thought to lose their
inner disks, suggesting that inner disks in intermediate mass stars are
dissipated rapidly after the accretion activity has fallen below a certain
level. We, further find a relatively tight correlation between strength of the
emission line and near-infrared excess due to inner disks in HAeBe stars,
indicating that the disks around Herbig Ae/Be stars cannot be entirely passive.
We suggest that this correlation can be understood within the frame work of the
puffed-up inner rim disk models if the radiation from the accretion shock is
also responsible for the disk heating.Comment: 39 pages, accepted for publication in Ap
- …