2,089 research outputs found
The Structure of the Proton in the LHC Precision Era
We review recent progress in the determination of the parton distribution
functions (PDFs) of the proton, with emphasis on the applications for precision
phenomenology at the Large Hadron Collider (LHC). First of all, we introduce
the general theoretical framework underlying the global QCD analysis of the
quark and gluon internal structure of protons. We then present a detailed
overview of the hard-scattering measurements, and the corresponding theory
predictions, that are used in state-of-the-art PDF fits. We emphasize here the
role that higher-order QCD and electroweak corrections play in the description
of recent high-precision collider data. We present the methodology used to
extract PDFs in global analyses, including the PDF parametrization strategy and
the definition and propagation of PDF uncertainties. Then we review and compare
the most recent releases from the various PDF fitting collaborations,
highlighting their differences and similarities. We discuss the role that QED
corrections and photon-initiated contributions play in modern PDF analysis. We
provide representative examples of the implications of PDF fits for
high-precision LHC phenomenological applications, such as Higgs coupling
measurements and searches for high-mass New Physics resonances. We conclude
this report by discussing some selected topics relevant for the future of PDF
determinations, including the treatment of theoretical uncertainties, the
connection with lattice QCD calculations, and the role of PDFs at future
high-energy colliders beyond the LHC.Comment: 170 pages, 85 figures, version to be published in Physics Report
Non-Hermitian dynamics of slowly-varying Hamiltonians
We develop a theoretical description of non-Hermitian time evolution that
accounts for the break- down of the adiabatic theorem. We obtain closed-form
expressions for the time-dependent state amplitudes, involving the complex
eigen-energies as well as inter-band Berry connections calculated using basis
sets from appropriately-chosen Schur decompositions. Using a two-level system
as an example, we show that our theory accurately captures the phenomenon of
"sudden transitions", where the system state abruptly jumps from one eigenstate
to another.Comment: 12 pages, 4 figure
Electroweak Chiral Lagrangian for a Hypercharge-universal Topcolor Model
Electroweak chiral Lagrangian for a hypercharge-universal topcolor model is
investigated. We find that the assignments of universal hypercharge improve the
results obtained previously from K.Lane's prototype natural TC2 model by
allowing a larger Z' mass resulting in a very small T parameter and the S
parameter is still around the order of +1Comment: 12 pages, 7 figure
Weyl points and topological nodal superfluids in a face-centered cubic optical lattice
We point out that a face-centered cubic (FCC) optical lattice, which can be
realised by a simple scheme using three lasers, provides one a highly
controllable platform for creating Weyl points and topological nodal
superfluids in ultracold atoms. In non-interacting systems, Weyl points
automatically arise in the Floquet band structure when shaking such FCC
lattices, and sophisticated design of the tunnelling is not required. More
interestingly, in the presence of attractive interaction between two hyperfine
spin states, which experience the same shaken FCC lattice, a three-dimensional
topological nodal superfluid emerges, and Weyl points show up as the gapless
points in the quasiparticle spectrum. One could either create a double Weyl
point of charge 2, or split it to two Weyl points of charge 1, which can be
moved in the momentum space by tuning the interactions. Correspondingly, the
Fermi arcs at the surface may be linked with each other or separated as
individual ones.Comment: 5 pages, 2 figures in the main text; 2 pages, 2 figures in the
supplemental materia
Towards Ultimate Parton Distributions at the High-Luminosity LHC
Since its start of data taking, the LHC has provided an impressive wealth of
information on the quark and gluon structure of the proton. Indeed, modern
global analyses of parton distribution functions (PDFs) include a wide range of
LHC measurements of processes such as the production of jets, electroweak gauge
bosons, and top quark pairs. In this work, we assess the ultimate constraining
power of LHC data on the PDFs that can be expected from the complete dataset,
in particular after the High-Luminosity (HL) phase, starting in around 2025.
The huge statistics of the HL-LHC, delivering ab to
ATLAS and CMS and ab to LHCb, will lead to an
extension of the kinematic coverage of PDF-sensitive measurements as well as to
an improvement in their statistical and systematic uncertainties. Here we
generate HL-LHC pseudo-data for different projections of the experimental
uncertainties, and then quantify the resulting constraints on the PDF4LHC15 set
by means of the Hessian profiling method. We find that HL-LHC measurements can
reduce PDF uncertainties by up to a factor of 2 to 4 in comparison to
state-of-the-art fits, leading to few-percent uncertainties for important
observables such as the Higgs boson transverse momentum distribution via
gluon-fusion. Our results illustrate the significant improvement in the
precision of PDF fits achievable from hadron collider data alone, and motivate
the continuation of the ongoing successful program of PDF-sensitive
measurements by the LHC collaborations.Comment: 30 pages, 20 figure
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