15,947 research outputs found
Brane solitons of (1,0) superconformal theories in six dimensions with hypermultiplets
We solve the Killing spinor equations of 6-dimensional (1,0) superconformal
theories which include hyper-multiplets in all cases. We show that the
solutions preserve 1,2,3,4 and 8 supersymmetries. We find models with self-dual
string solitons which are smooth and supported by instantons with an arbitrary
gauge group, and 3-brane solitons as expected from the M-brane intersection
rules.Comment: 13 page
Spinorial geometry, horizons and superconformal symmetry in six dimensions
The spinorial geometry method of solving Killing spinor equations is reviewed
as it applies to 6-dimensional (1,0) supergravity. In particular, it is
explained how the method is used to identify both the fractions of
supersymmetry preserved by and the geometry of all supersymmetric backgrounds.
Then two applications are described to systems that exhibit superconformal
symmetry. The first is the proof that some 6-dimensional black hole horizons
are locally isometric to , where is
diffeomeorphic to . The second one is a description of all supersymmetric
solutions of 6-dimensional (1,0) superconformal theories and in particular of
their brane solitons.Comment: 51 pages, accepted for publication in CQG, additional references
adde
Superstring dualities and p-brane bound states
We show that the M-theory/IIA and IIA/IIB superstring dualities together with
the diffeomorphism invariance of the underlying theories require the presence
of certain p-brane bound states in IIA and IIB superstring theories preserving
1/2 of the spacetime supersymmetry. We then confirm the existence of IIA and
IIB supergravity solutions having the appropriate p-brane bound states
interpretation.Comment: 21 pages, Phyzzx, Minor corrections, Version that will appear in
Nucl. Phys.
Dominant QCD Backgrounds in Higgs Boson Analyses at the LHC: A Study of pp -> t anti-t + 2 jets at Next-To-Leading Order
We report the results of a next-to-leading order simulation of top quark pair
production in association with two jets. With our inclusive cuts, we show that
the corrections with respect to leading order are negative and small, reaching
11%. The error obtained by scale variation is of the same order. Additionally,
we reproduce the result of a previous study of top quark pair production in
association with a single jet.Comment: 4 pages, 5 figures, 1 tabl
Assault on the NLO Wishlist: pp -> tt bb
We present the results of a next-to-leading order calculation of QCD
corrections to the production of an on-shell top-anti-top quark pair in
association with two flavored b-jets. Besides studying the total cross section
and its scale dependence, we give several differential distributions. Where
comparable, our results agree with a previous analysis. While the process under
scrutiny is of major relevance for Higgs boson searches at the LHC, we use it
to demonstrate the ability of our system built around Helac-Phegas to tackle
complete calculations at the frontier of current studies for the LHC. On the
technical side, we show how the virtual corrections are efficiently computed
with Helac-1Loop, based on the OPP method and the reduction code CutTools,
using reweighting and Monte Carlo over color configurations and polarizations.
As far as the real corrections are concerned, we use the recently published
Helac-Dipoles package. In connection with improvements of the latter, we give
the last missing integrated dipole formulae necessary for a complete
implementation of phase space restriction dependence in the massive dipole
subtraction formalism.Comment: 19 pages, 11 figures, 2 tables. References added, version to appear
in JHE
(1,0) superconformal theories in six dimensions and Killing spinor equations
We solve the Killing spinor equations of 6-dimensional (1,0) superconformal
theories in all cases. In particular, we derive the conditions on the fields
imposed by the Killing spinor equations and demonstrate that these depend on
the isotropy group of the Killing spinors. We focus on the models proposed by
Samtleben et al in \cite{ssw} and find that there are solutions preserving 1,2,
4 and 8 supersymmetries. We also explore the solutions which preserve 4
supersymmetries and find that many models admit string and 3-brane solitons as
expected from the M-brane intersection rules. The string solitons are smooth
regulated by the moduli of instanton configurations.Comment: 26 page
Identification issues in models for underreported counts
In this note we study the conditions under which leading models for underreported counts are identified. In particular, we highlight a peculiar identification problem that afflicts two of the most popular models in this class.
Top-antitop pair hadroproduction in association with a heavy boson at the NLO QCD accuracy + Parton Shower
The PowHel framework allows to make predictions of total and differential
cross-sections of multiparticle hadroproduction processes at both NLO QCD
accuracy and NLO QCD matched to Parton Shower, on the basis of the interface
between the POWHEG-BOX and HELAC-NLO codes. It has already been applied to
study several processes involving a top-antitop pair in association with a
third particle or hadronic jet. Our most recent predictions concern
top-antitop-V hadroproduction (with V = W or Z), at both parton and hadron
level, by considering different decay channels (hadronic and leptonic) of the
heavy particles. In particular, we show the results of our phenomenological
analyses under the same system of cuts also recently adopted by the CMS
collaboration at LHC.Comment: 4 pages, 2 figures, Proceedings of TOP 2012 - 5th International
Workshop on Top Quark Physics, September 16 - 21 2012, Winchester, U
Z0 - boson production in association with a top anti-top pair at NLO accuracy with parton shower effects
We present predictions for the production cross section of a Standard Model
Z0-boson in association with a top-antitop pair at the next-to-leading order
accuracy in QCD, matched with shower Monte Carlo programs to evolve the system
down to the hadronization energy scale. We adopt a framework based on three
well established numerical codes, namely the POWHEG-BOX, used for computing the
cross section, HELAC-NLO, which generates all necessary input matrix elements,
and finally a parton shower program, such as PYTHIA or HERWIG, which allows for
including t-quark and Z0-boson decays at the leading order accuracy and
generates shower emissions, hadronization and hadron decays.Comment: 10 pages, 5 figures; found and corrected a bug in the
phenomenological analysis, just affecting Fig.4 - 5 that turn out to change
slightly with respect to our previous version and the cross-section values
after all cuts. Conclusions qualitatively unchange
- …