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Amsterdam-Zuidoost, Netherlands

Aybat S.M.,Nikhef Theory Group | Prokudin A.,Jefferson Lab | Rogers T.C.,State University of New York at Stony Brook
Physical Review Letters | Year: 2012

The Sivers transverse single spin asymmetry (TSSA) is calculated and compared at different scales using the transverse-momentum-dependent (TMD) evolution equations applied to previously existing extractions. We apply the Collins-Soper-Sterman (CSS) formalism, using the version recently developed by Collins. Our calculations rely on the universality properties of TMD functions that follow from the TMD-factorization theorem. Accordingly, the nonperturbative input is fixed by earlier experimental measurements, including both polarized semi-inclusive deep inelastic scattering (SIDIS) and unpolarized Drell-Yan (DY) scattering. It is shown that recent preliminary COMPASS measurements are consistent with the suppression prescribed by TMD evolution. © 2012 American Physical Society. Source


de Adelhart Toorop R.,Nikhef Theory Group | Feruglio F.,University of Padua | Hagedorn C.,University of Padua
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We show that a non-vanishing angle θ13 of order 0.1 can be predicted in the framework of discrete flavour symmetries. We assume that left-handed leptons transform as triplets under a group Gf which is broken in such a way that neutrino and charged lepton sectors remain invariant under the subgroups Gν and Ge of Gf, respectively. In this limit mixing angles and the Dirac CP violating phase δ CP are determined. By choosing G f=δ(6n 2) (n=4,8), Gν=Z 2×Z 2 and G e=Z 3 we find sin2θ13=0.045(0.011) for n=4(8). At the same time θ23 and θ12 remain close to their experimental best fit values, particularly in the case n=8, where sin2θ23θ0.424 and sin2θ12θ0.337. δCP is predicted to be 0 or Π so that CP is conserved in our examples. © 2011 Elsevier B.V. Source


Tentyukov M.,Karlsruhe Institute of Technology | Vermaseren J.A.M.,Nikhef Theory Group
Computer Physics Communications | Year: 2010

We present TFORM, the version of the symbolic manipulation system FORM that can make simultaneous use of several processors in a shared memory architecture. The implementation uses Posix threads, also called pthreads, and is therefore easily portable between various operating systems. Most existing FORM programs will be able to take advantage of the increased processing power, without the need for modifications. In some cases some minor additions may be needed. For a computer with two processors a typical improvement factor in the running time is 1.7 when compared to the traditional version of FORM. In the case of computers with 4 processors a typical improvement factor in the execution time is slightly above 3. © 2010 Elsevier B.V. All rights reserved. Source


Butter D.,Nikhef Theory Group
Journal of High Energy Physics | Year: 2015

Abstract: Projective superspace provides a natural framework for the construction of actions coupling hypermultiplets to conformal supergravity. We review how the off-shell actions are formulated in superspace and then discuss how to eliminate the infinite number of auxiliary fields to produce an on-shell N=2$$ \mathcal{N}=2 $$ supersymmetric sigma model, with the target space corresponding to a generic 4n-dimensional hyperkähler cone. We show how the component action coupling the hypermultiplets to conformal supergravity may be constructed starting from curved superspace. The superspace origin of the geometric data — the hyperkähler potential, complex structures, and any gauged isometries — is also addressed. © 2015, The Author(s). Source


Gupta R.K.,Nikhef Theory Group | Lal S.,Harish Chandra Research Institute
Journal of High Energy Physics | Year: 2012

We calculate the one-loop partition function for a massless arbitrary-spin field on quotients of a general dimensional AdS background using the results of arXiv:1103.3627. We use these results to compute the one-loop partition function for a Vasiliev theory in AdS5. An interesting form of the answer, suggestive of a vacuum character of an enhanced symmetry algebra is obtained. We also observe a close connection between the partition function for this Vasiliev theory and the d-dimensional MacMahon function. © SISSA 2012. Source

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