9,991 research outputs found
Note on lattice regularization and equal-time correlators for parton distribution functions
We show that a recent interesting idea to circumvent the difficulties with
the continuation of parton distribution functions to the Euclidean region, that
consists in looking at equal time correlators between proton states of infinite
momentum, encounters some problems related to the power divergent mixing
pattern of DIS operators, when implemented within the lattice regularization.Comment: 15 pages, no figures, Physical Review D (2017
On lattice chiral gauge theories
The Smit-Swift-Aoki formulation of a lattice chiral gauge theory is presented. In this formulation the Wilson and other non invariant terms in the action are made gauge invariant by the coupling with a nonlinear auxilary scalar field, omega. It is shown that omega decouples from the physical states only if appropriate parameters are tuned so as to satisfy a set of BRST identities. In addition, explicit ghost fields are necessary to ensure decoupling. These theories can give rise to the correct continuum limit. Similar considerations apply to schemes with mirror fermions. Simpler cases with a global chiral symmetry are discussed and it is shown that the theory becomes free at decoupling. Recent numerical simulations agree with those considerations
Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
A solar eruption after a flare on 7 Jun 2011 produced EUV-bright impacts of
fallbacks far from the eruption site, observed with the Solar Dynamics
Observatory. These impacts can be taken as a template for the impact of stellar
accretion flows. Broad red-shifted UV lines have been commonly observed in
young accreting stars. Here we study the emission from the impacts in the
Atmospheric Imaging Assembly's UV channels and compare the inferred velocity
distribution to stellar observations. We model the impacts with 2D hydrodynamic
simulations. We find that the localised UV 1600A emission and its timing with
respect to the EUV emission can be explained by the impact of a cloud of
fragments. The first impacts produce strong initial upflows. The following
fragments are hit and shocked by these upflows. The UV emission comes mostly
from the shocked front shell of the fragments while they are still falling, and
is therefore redshifted when observed from above. The EUV emission instead
continues from the hot surface layer that is fed by the impacts. Fragmented
accretion can therefore explain broad redshifted UV lines (e.g. C IV 1550A) to
speeds around 400 km/s observed in accreting young stellar objects.Comment: 12 pages, 4 figures (movies available upon request), accepted for
publicatio
Gemini optical observations of binary millisecond-pulsars
Milli-second pulsars (MSPs) are rapidly spinning neutron stars, with spin
periods P_s <= 10 ms, which have been most likely spun up after a phase of
matter accretion from a companion star. In this work we present the results of
the search for the companion stars of four binary milli-second pulsars, carried
out with archival data from the Gemini South telescope. Based upon a very good
positional coincidence with the pulsar radio coordinates, we likely identified
the companion stars to three MSPs, namely PSRJ0614-3329 (g=21.95 +- 0.05),
J1231-1411 (g=25.40 +-0.23), and J2017+0603 (g=24.72 +- 0.28). For the last
pulsar (PSRJ0613-0200) the identification was hampered by the presence of a
bright star (g=16 +- 0.03) at \sim 2" from the pulsar radio coordinates and we
could only set 3-sigma upper limits of g=25.0, r= 24.3, and i= 24.2 on the
magnitudes of its companion star. The candidate companion stars to
PSRJ0614-3329, J1231-1411, and J2017+0603 can be tentatively identified as He
white dwarfs (WDs) on the basis of their optical colours and brightness and the
comparison with stellar model tracks. From the comparison of our multi-band
photometry with stellar model tracks we also obtained possible ranges on the
mass, temperature, and gravity of the candidate WD companions to these three
MSPs. Optical spectroscopy observations are needed to confirm their possible
classification as He WDs and accurately measure their stellar parameters.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in MNRA
CV/TCR Control System Perspectives
At present, 35% of the CERN technical infrastructure points being monitored by the TCR are related to CV facilities. The adaptation of the CV systems to the LHC and the new experimental areas is leading to a re-engineering of all their control and monitoring systems in order to reach the more demanding requirements of the LHC era in terms of reliability and efficiency. In parallel, the TCR is redefining its role and establishing the means to continue providing a high-quality monitoring service to the community of CERN. The common aim is to achieve a smooth evolution from the existing systems to the new ones during the whole upgrading process. The integration of the CV control systems into a coherent TCR control and monitoring system requires the development and implementation of the appropriate technical solutions by a joint team in charge of co-ordinating the individual efforts and resources
Preference Theory and Low Fertility: A Comparative Perspective
The discussion on the causes of the most recent fertility decline in Europe, and in particular on the emergence of lowest low fertility, emphasises the relevance of cultural factors in addition to economic ones. Being part of such a cultural framework, the heterogeneity of preferences concerning the "career vs. family" dichotomy has been systematised in the "Preference Theory" approach developed by Catherine Hakim. So far, however, this heterogeneity in preferences has been underinvestigated in a comparative framework. This paper makes use of new comparative data from the 2004/05 Round of the European Social Survey to test the links between individual-level preferences and both fertility outcomes and intentions in a variety of social settings. Results confirm a link between work-family lifestyle preferences and realised fertility in a variety of European countries, while they do not support the relevance of lifestyle preferences for fertility intentions.Preference Theory, low and lowest low fertility, Europe, European Social Survey, welfare regime.
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
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