| 1. |
- Aoyama, T., et al.
(författare)
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The anomalous magnetic moment of the muon in the Standard Model
- 2020
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Ingår i: Physics reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 887, s. 1-166
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Forskningsöversikt (refereegranskat)abstract
- We review the present status of the Standard Model calculation of the anomalous magnetic moment of the muon. This is performed in a perturbative expansion in the fine-structure constant α and is broken down into pure QED, electroweak, and hadronic contributions. The pure QED contribution is by far the largest and has been evaluated up to and including O(α5) with negligible numerical uncertainty. The electroweak contribution is suppressed by (mμ/MW)2 and only shows up at the level of the seventh significant digit. It has been evaluated up to two loops and is known to better than one percent. Hadronic contributions are the most difficult to calculate and are responsible for almost all of the theoretical uncertainty. The leading hadronic contribution appears at O(α2) and is due to hadronic vacuum polarization, whereas at O(α3) the hadronic light-by-light scattering contribution appears. Given the low characteristic scale of this observable, these contributions have to be calculated with nonperturbative methods, in particular, dispersion relations and the lattice approach to QCD. The largest part of this review is dedicated to a detailed account of recent efforts to improve the calculation of these two contributions with either a data-driven, dispersive approach, or a first-principle, lattice-QCD approach. The final result reads aμSM = 116 591 810(43) x 10-11 and is smaller than the Brookhaven measurement by 3.7 σ. The experimental uncertainty will soon be reduced by up to a factor four by the new experiment currently running at Fermilab, and also by the future J-PARC experiment. This and the prospects to further reduce the theoretical uncertainty in the near future - which are also discussed here - make this quantity one of the most promising places to look for evidence of new physics.
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| 2. |
- Baumgart, Mona, et al.
(författare)
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Design of buried charged networks in artificial proteins
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Soluble proteins are universally packed with a hydrophobic core and a polar surface that drive the protein folding process. Yet charged networks within the central protein core are often indispensable for the biological function. Here, we show that natural buried ion-pairs are stabilised by amphiphilic residues that electrostatically shield the charged motif from its surroundings to gain structural stability. To explore this effect, we build artificial proteins with buried ion-pairs by combining directed computational design and biophysical experiments. Our findings illustrate how perturbation in charged networks can introduce structural rearrangements to compensate for desolvation effects. We validate the physical principles by resolving high-resolution atomic structures of the artificial proteins that are resistant towards unfolding at extreme temperatures and harsh chemical conditions. Our findings provide a molecular understanding of functional charged networks and how point mutations may alter the protein's conformational landscape.
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| 3. |
- Bernard, C., et al.
(författare)
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Semileptonic kaon decay in staggered chiral perturbation theory
- 2014
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 89:5
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Tidskriftsartikel (refereegranskat)abstract
- The determination of vertical bar V-us vertical bar from kaon semileptonic decays requires the value of the form factor f(+)(q(2) = 0), which can be calculated precisely on the lattice. We provide the one-loop partially quenched staggered chiral perturbation theory expressions that may be employed to analyze staggered simulations of f(+)(q(2)) with three light flavors. We consider both the case of a mixed action, where the valence and sea sectors have different staggered actions, and the standard case, where these actions are the same. The momentum transfer q(2) of the form factor is allowed to have an arbitrary value. We give results for the generic situation where the u, d, and s quark masses are all different, N-f = 1 + 1 + 1, and for the isospin limit, N-f = 2 + 1. The expression we obtain for f(+)(q(2)) is independent of the mass of the ( valence) spectator quark. In the limit of vanishing lattice spacing, our results reduce to the one-loop continuum partially quenched expression for f(+)(q(2)), which has not previously been reported in the literature for the N-f = 1 + 1 + 1 case. Our expressions have already been used in staggered lattice analyses of f(+)(0) and should prove useful in future calculations as well.
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| 4. |
- Bijnens, Johan, et al.
(författare)
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Hadronic matrix elements for kaons
- 2004
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Ingår i: Nuclear Physics B - Proceedings Supplements. - : Elsevier BV. - 0920-5632. ; 133, s. 245-251
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Tidskriftsartikel (refereegranskat)abstract
- We review some work done by us calculating matrix elements for Kaons. Emphasis is put on the matrix elements which are relevant to predict non-leptonic Kaon CP violating observables. In particular, we recall our results for the (B) over cap (K) parameter which governs the (K-0) over bar - K-0 mixing and update our results for epsilon(K)' including estimated all-higher-order CHPT corrections and the new results from recent analytical calculations of the DeltaI = 3/2 component. Some comments on future prospects on calculating matrix elements for Kaons are also added.
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| 5. |
- Bijnens, Johan, et al.
(författare)
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QCD Short-distance constraints and hadronic approximations
- 2003
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :4: 055
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses a general class of ladder resummation inspired hadronic approximations. It is found that this approach naturally reproduces many successes of single meson per channel saturation models (e.g. VMD) and NJL based models. In particular the existence of a constituent quark mass and a gap equation follows naturally. We construct an approximation that satisfies a large set of QCD short-distance and large N-c constraints and reproduces many hadronic observables. We show how there exists in general a problem between QCD short-distance constraints for Green Functions and those for form factors and cross-sections following from the quark-counting rule. This problem while expected for Green functions that do not vanish in purely perturbative QCD also persists for many Green functions that are order parameters.
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| 6. |
- Bijnens, Johan, et al.
(författare)
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The B-K kaon parameter in the chiral limit
- 2006
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We introduce four-point functions in the hadronic ladder resummation approach to large N-c QCD Green functions. We determine the relevant one to calculate the B-K kaon parameter in the chiral limit. This four-point function contains both the large momenta QCD OPE and the small momenta ChPT at NLO limits, analytically. We get (B) over cap (X)(K) = 0.38 +/- 0.15. We also give the ChPT result at NLO for the relevant four-point function to calculate B-K outside the chiral limit, while the leading QCD OPE is the same as the chiral limit one.
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| 7. |
- Donetti, L., et al.
(författare)
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Hole effective mass in silicon inversion layers with different substrate orientations and channel directions
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:6, s. 063711-
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Tidskriftsartikel (refereegranskat)abstract
- We explore the possibility to define an effective mass parameter to describe hole transport in inversion layers in bulk MOSFETs and silicon-on-insulator devices. To do so, we employ an accurate and computationally efficient self-consistent simulator based on the six-band k . p model. The valence band structure is computed for different substrate orientations and silicon layer thicknesses and is then characterized through the calculation of different effective masses taking account of the channel direction. The effective masses for quantization and density of states are extracted from the computed energy levels and subband populations, respectively. For the transport mass, a weighted averaging procedure is introduced and justified by comparing the results with hole mobility from experiments and simulations.
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| 8. |
- Donetti, L., et al.
(författare)
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On the effective mass of holes in inversion layers
- 2011
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Ingår i: International Conference on Ultimate Integration on Silicon. - 9781457700903 ; , s. 50-53
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Konferensbidrag (refereegranskat)abstract
- We study hole inversion layers in bulk MOSFETs and silicon-on-insulator devices employing a self-consistent simulator based on the six-band kp model. Valence Band structure is computed for different device orientations and silicon layer thicknesses, and then it is characterized through the calculation of different effective masses.
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| 9. |
- Gamiz, E, et al.
(författare)
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Matching the electroweak penguins Q(7) and Q(8)
- 2003
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Ingår i: Nuclear Physics B - Proceedings Supplements (Proceedings of the QCD 02 9th High-Energy Physics International Conference on Quantum ChromoDynamics). - 0920-5632. ; 121, s. 195-198
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Konferensbidrag (refereegranskat)abstract
- We report on recent advances on the computation of the matrix elements of the electroweak penguins Q(7) and Q(8) which are relevant for the DeltaI = 3/2 contribution to epsilon'(K) in the chiral limit. The matching of scale and scheme dependences between Wilson coefficients and these matrix elements is done analytically at NLO in alpha(S).
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| 10. |
- Mühlbauer, Max E., et al.
(författare)
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Functional Dynamics of an Ancient Membrane-Bound Hydrogenase
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:49, s. 20873-20883
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Tidskriftsartikel (refereegranskat)abstract
- The membrane-bound hydrogenase (Mbh) is a redox-driven Na+/H+ transporter that employs the energy from hydrogen gas (H2) production to catalyze proton pumping and Na+/H+ exchange across cytoplasmic membranes of archaea. Despite a recently resolved structure of this ancient energy-transducing enzyme [Yu et al. Cell2018, 173, 1636–1649], the molecular principles of its redox-driven ion-transport mechanism remain puzzling and of major interest for understanding bioenergetic principles of early cells. Here we use atomistic molecular dynamics (MD) simulations in combination with data clustering methods and quantum chemical calculations to probe principles underlying proton reduction as well as proton and sodium transport in Mbh from the hyperthermophilic archaeon Pyrococcus furiosus. We identify putative Na+ binding sites and proton pathways leading across the membrane and to the NiFe-active center as well as conformational changes that regulate ion uptake. We suggest that Na+ binding and protonation changes at a putative ion-binding site couple to proton transfer across the antiporter-like MbhH subunit by modulating the conformational state of a conserved ion pair at the subunit interface. Our findings illustrate conserved coupling principles within the complex I superfamily and provide functional insight into archaeal energy transduction mechanisms.
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