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Quantum Mechanical Formulation of the Busch Theorem
No full textElectron vortex beams offer unique opportunities for the study of chiral or magnetic structures in electron microscopes and of fundamental effects of quantum interference in particle physics. Immersing a cathode in a solenoid field presents a highly efficient and flexible method for the generation of vortex electron beams which is utilized at accelerators, but has not yet been realized in an electron microscope. The conditions for the generation of vortex beams with quantized orbital angular momentum from an immersed cathode in an electron microscope are discussed, and general possibilities of this technique for the production of vortex beams of other charged particles are pointed out
Precision Global Determination of the Decay Rate
No full textWe perform the first global fit to inclusive measurements using a model-independent treatment of the nonperturbative -quark distribution function, with next-to-next-to-leading logarithmic resummation and fixed-order contributions. The normalization of the decay rate, given by , is sensitive to physics beyond the Standard Model (SM). We determine , in good agreement with the SM prediction, and the -quark mass . Our results suggest that the uncertainties in the extracted rate have been underestimated by up to a factor of two, leaving more room for beyond-SM contributions
Two-loop coefficient function for DVCS: Vector contributions
No full textUsing the approach based on conformal symmetry we calculate the two-loop coefficient function for the vector flavor-nonsinglet contribution to deeply-virtual Compton scattering (DVCS). The analytic expression for the coefficient function in momentum fraction space is presented in the scheme. The corresponding next-to-next-to-leading order correction to the Compton form factor for a simple model of the generalized parton distribution appears to be rather large: a factor two smaller than the next-to-leading order correction, approximately \% of the tree level result in the bulk of the kinematic range, for ~GeV
4D SCFTs and spin chains
No full textThis is the writeup of the lectures given at the Winter School ‘YRISW 2018’ to appear in a special issue of J. Phys. A: Math. Theor. In the first part of these lecture notes we review some important facts about 4D SCFTs. We begin with basic textbook material, the supersymmetry algebra and its massless representations and the construction of Lagrangians using superspace. Then we turn to more modern topics, the study of the SCA and its representation theory. Our intention is to understand how much we can learn from representation theory alone, even about the dynamics of SCFTs. In the second part of the notes we use these tools to construct spin chains for SCFTs, the spectral problem of which computes anomalous dimensions of local operators. We discuss their novel features comparing them with their counterparts in SYM and search for possible integrability structures that emerge
Electronic-structure calculations for nonisothermal warm dense matter
No full textWarm dense matter (WDM) is an exotic state of matter that is inherently difficult to model theoretically, due to the fact that the thermal Coulomb coupling and quantum effects are comparable in magnitude and must be treated on equal footing, foregoing the employment of conventional methods from either plasma physics or condensed-matter physics. Our work focuses on describing electronic states present in a transient, nonisothermal WDM state, where electrons become hot and ions remain cold, during the first 10–100 fs after the irradiation of a solid sample with an intense femtosecond x-ray pulse. We present a methodology, combining the finite-temperature Hartree-Fock-Slater approach with the Bloch-wave approach within a periodic atomic lattice, implemented in a new toolkit, xcrystal. In xcrystal, electronic states are represented in a hybrid basis comprising plane waves and localized core orbitals on a radial pseudospectral grid. This hybrid basis ensures a high numerical efficiency as highly localized states need not be described using plane waves. Additionally, these core orbitals are responsive to the presence of delocalized plasma electrons through an interwoven optimization between inner-shell and outer-shell electronic states employed in xcrystal. Therefore, not only does xcrystal model the plasma electrons efficiently, it also allows for access to inner-shell modifications at high electronic temperatures. To benchmark our method, we calculate -shell threshold energies of x-ray-excited solid-density aluminum as well as the ionization potential depression and show their agreement with experiment. In comparing our method with other theoretical models, we conclude that the incorporation of optimized inner-shell orbitals is essential to obtain accurate results, and we find that the inclusion of the full crystal structure has a limited effect. Furthermore, we obtain temperature-dependent band structure predictions at WDM conditions, up to temperatures of 100 eV, which, to the best of our knowledge, are the first of their kind for this nonisothermal system. We expect that our proposed methodology will aid in the theoretical description of nonisothermal WDM, as well as advance the understanding of this exotic state of matter
Approximate four-loop QCD corrections to the Higgs-boson production cross section
No full textWe study the soft and collinear contributions to inclusive Higgs-boson production in gluon-gluon fusion at four loops. Using recent progress for the quark and gluon form factors and Mellin moments of splitting functions, we are able to complete the soft-gluon enhanced contributions exactly in the limit of a large number of colours, and to a sufficiently accurate numerical accuracy for QCD. The four-loop soft and virtual contributions increase the QCD cross section at 14 TeV by 2.7% and 0.2% for the standard choices and of the renormalization scale, and reduce the scale uncertainty to below 3% . As by-products, we derive the complete term for the gluon-gluon splitting function at four loops and its purely Abelian contributions at five loops, and provide a numerical result for the single pole of the four-loop gluon form factor in dimensional regularization. Finally we present the closely related fourth-order coefficients D4 for the soft-gluon exponentiation of Higgs-boson and Drell-Yan lepton-pair production
Search for a light pseudoscalar Higgs boson in the boosted final state in proton-proton collisions at 13 TeV
No full textA search for a light pseudoscalar Higgs boson (a) decaying from the 125 GeV (or a heavier) scalar Higgs boson (H) is performed using the 2016 LHC proton-proton collision data at 13 TeV, corresponding to an integrated luminosity of 35.9 fb, collected by the CMS experiment. The analysis considers gluon fusion and vector boson fusion production of the H, followed by the decay H aa , and considers pseudoscalar masses in the range 3.6 21 GeV. Because of the large mass difference between the H and the a bosons and the small masses of the a boson decay products, both the and the pairs have high Lorentz boost and are collimated. The reconstruction efficiency is increased by modifying the standard technique for hadronic lepton decay reconstruction to account for a nearby muon. No significant signal is observed. Model-independent limits are set at 95% confidence level, as a function of , on the branching fraction () for H aa , down to 1.5 (2.0) for 125 (300) GeV. Model-dependent limits on (H aa) are set within the context of two Higgs doublets plus singlet models, with the most stringent results obtained for Type-III models. These results extend current LHC searches for heavier a bosons that decay to resolved lepton pairs and provide the first such bounds for an H boson with a mass above 125 GeV