3,060 research outputs found
Symmetric discrete quotients of supersymmetric Hpp-waves and spin structures
We explore the importance of the choice of spin structure in determining the
amount of supersymmetry preserved by a symmetric M-theory background
constructed by quotienting a supersymmetric Hpp-wave with a discrete subgroup
in the centraliser of its isometry group.Comment: 16 pages, 2 table
Nuclear PDFs from the LHeC perspective
We study the prospects for constraining the nuclear parton distribution
functions by small-x deep inelastic scattering. Performing a global fit of
nuclear parton distribution functions including a sample of pseudodata
representing expected measurements at the planned LHeC collider, we demonstrate
that the accuracy of the present nuclear parton distributions could be be
improved substantially. We also discuss the impact of flavour-tagged data.Comment: A transcription of the talk given in XXI International Workshop on
Deep-Inelastic Scattering and Related Subjects, Marseilles, Franc
Binary systems in Palatini-f(R) gravity
We consider compact binary systems in f(R) gravity theories in the Palatini
approach and calculate the post-Newtonian parameters to the 1.5PN order using
the method of Direct Integration of the Relaxed Einstein equations (DIRE). The
Palatini-type modifications of gravity can be formulated as Einsteins gravity
with modified response to matter sources, and it is shown in detail how to
treat these correctly within the DIRE formalism. Our results explicitly confirm
the expectation that for binary black holes the new effects can be absorbed
into redefinitions of the binary masses, rendering such systems observationally
identical to general relativity.Comment: 11 page
Dijets in p+Pb collisions and their quantitative constraints for nuclear PDFs
We present a perturbative QCD analysis concerning the production of high-pT
dijets in p+Pb collisions at the LHC. The next-to-leading order corrections,
scale variations and free-proton PDF uncertainties are found to have only a
relatively small influence on the normalized dijet rapidity distributions.
Interestingly, however, these novel observables prove to retain substantial
sensitivity to the nuclear effects in the PDFs. Especially, they serve as a
more robust probe of the nuclear gluon densities at , than e.g. the
inclusive hadron production. We confront our calculations with the recent data
by the CMS collaboration. These preliminary data lend striking support to the
gluon antishadowing similar to that in the EPS09 nuclear PDFs.Comment: Transcription of the talk given in Quark Matter 2014 conferenc
Constraining nPDFs with inclusive pions and direct photons at forward rapidities in p+Pb collisions at the LHC
In this talk, we present NLO pQCD predictions for inclusive pion and direct
photon nuclear modifications in p+Pb collisions at mid- and forward rapidities
at the LHC. In addition to the minimum bias predictions, we also address the
centrality dependence with spatially dependent nuclear PDFs. To understand
which regions of the nuclear momentum fraction these observables
predominantly probe, we present also the underlying distributions at
different rapidities. We are led to conclude that the isolated photons at
forward rapidities are more sensitive to the small- dynamics than the
inclusive pions.Comment: 4 pages, 5 figures. Prepared for the Proceedings of "Hard Probes
2013", the 6th International Conference on Hard and Electromagnetic Probes of
High-Energy Nuclear Collisions, Stellenbosch, South Africa, November 4-8,
201
Event-by-event hydrodynamics and elliptic flow from fluctuating initial state
We develop a framework for event-by-event ideal hydrodynamics to study the
differential elliptic flow which is measured at different centralities in Au+Au
collisions at Relativistic Heavy Ion Collider (RHIC). Fluctuating initial
energy density profiles, which here are the event-by-event analogues of the eWN
profiles, are created using a Monte Carlo Glauber model. Using the same event
plane method for obtaining as in the data analysis, we can reproduce both
the measured centrality dependence and the shape of charged-particle
elliptic flow up to ~GeV. We also consider the relation of elliptic
flow to the initial state eccentricity using different reference planes, and
discuss the correlation between the physical event plane and the initial
participant plane. Our results demonstrate that event-by-event hydrodynamics
with initial state fluctuations must be accounted for before a meaningful lower
limit for viscosity can be obtained from elliptic flow data.Comment: 10 pages, 7 figures; v2: figures updated and v2{PP} results adde
ADM Analysis of Gravity Models within the Framework of Bimetric Variational Formalism
Bimetric variational formalism was recently employed to construct novel
bimetric gravity models. In these models an affine connection is generated by
an additional tensor field which is independent of the physical metric. In this
work we demonstrate how the ADM decomposition can be applied to study such
models and provide some technical intermediate details. Using ADM decomposition
we are able to prove that a linear model is unstable as has previously been
indicated by perturbative analysis. Moreover, we show that it is also very
difficult if not impossible to construct a non-linear model which is ghost-free
within the framework of bimetric variational formalism. However, we demonstrate
that viable models are possible along similar lines of thought. To this end, we
consider a set up in which the affine connection is a variation of the
Levi-Civita one. As a proof of principle we construct a gravity model with a
massless scalar field obtained this way.Comment: 16 pages. Version to be published in JCA
Centrality dependence of inclusive prompt photon production in d+Au, Au+Au, p+Pb, and Pb+Pb collisions
We calculate the centrality dependence of the midrapidity nuclear
modification for inclusive prompt photon production in d+Au and Au+Au
collisions at RHIC and in p+Pb and Pb+Pb collisions at the LHC. Our results,
using the recent spatially dependent nuclear PDF set EPS09s, are consistent
with the existing high-pT data from the PHENIX and CMS collaborations. The good
agreement even in the case of nucleus+nucleus collisions suggests that the
high-pT direct photon production is not significantly altered by the strongly
interacting medium produced in such collisions. We find the centrality
dependence of the nuclear modifications generally rather weak but perhaps
measurable at low pT.Comment: 14 pages, 7 figures; v2: Corrected a small inaccuracy related to the
scale choice mu=pT/2 in figures 1, 2, and
The present status of the EPS nuclear PDFs
The recent global analyses of the nuclear parton distribution functions
(nPDFs) lend support to the validity of the factorization theorem of QCD in
high-energy processes involving bound nucleons. With a special attention on our
latest global analysis EPS09, we review the recent developements in the domain
of nuclear PDFs.Comment: A talk given in 35th International Conference of High Energy Physic
Transiting exoplanet candidates from K2 Campaigns 5 and 6
We introduce a new transit search and vetting pipeline for observations from
the K2 mission, and present the candidate transiting planets identified by this
pipeline out of the targets in Campaigns 5 and 6. Our pipeline uses the
Gaussian Process-based K2SC code to correct for the K2 pointing systematics and
simultaneously model stellar variability. The systematics-corrected,
variability-detrended light curves are searched for transits with the Box Least
Squares method, and a period-dependent detection threshold is used to generate
a preliminary candidate list. Two or three individuals vet each candidate
manually to produce the final candidate list, using a set of
automatically-generated transit fits and assorted diagnostic tests to inform
the vetting. We detect 147 single-planet system candidates and 5 multi-planet
systems, independently recovering the previously-published hot~Jupiters EPIC
212110888b, WASP-55b (EPIC 212300977b) and Qatar-2b (EPIC 212756297b). We also
report the outcome of reconnaissance spectroscopy carried out for all
candidates with Kepler magnitude Kp < 13, identifying 12 targets as likely
false positives. We compare our results to those of other K2 transit search
pipelines, noting that ours performs particularly well for variable and/or
active stars, but that the results are very similar overall. All the light
curves and code used in the transit search and vetting process are publicly
available, as are the follow-up spectra.Comment: Accepted to MNRA
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