[ NIKHEF theory group ]

Purpose

To meet, discuss, collaborate, generate ideas, share expertise, in the context of the FOM programme "Higgs as Probe and Portal"

We hope to see you here!

Agenda September 29

Time: 10.00 - 17.00
  • 10.30 - 11.00, H320:

    Tom van Daal (Nikhef)
    Disentangling colors in Drell-Yan scattering

    Abstract: Factorization forms the cornerstone of QCD phenomenology. For Drell-Yan scattering it means that the cross-section can be factorized into a product of a calculable hard part and two parton distribution functions (PDFs). For the usual PDFs only the motion of partons collinear to the parent hadron is taken into account. Going beyond collinear kinematics, one can define 3D density functions called transverse momentum distributions (TMDs). Recently there has been some discussion about whether a particular contribution to the Drell-Yan cross-section involving the so-called Boer-Mulders TMD is suppressed due to color entanglement effects, stemming from the nonabelian nature of QCD. This effect could lead to a violation of factorization. We have investigated this issue by performing an explicit model calculation along the lines of the Drell-Yan factorization proof and find that this particular contribution completely disentangles in color space, leading to the expected 1/N_c overall color factor.



  • 13.00 - 13.30, H320
    Plot of the Month/Pie of the Month



  • 14.00 - 15.00, H320
    Student meeting/discussion:

    Manus Visser (UVA)
    Verlinde’s theory of emergent gravity: a status report.

    Abstract: Last year Verlinde proposed that the flattening of galaxy rotation curves is due to a modification of Einstein gravity at long distances. I will explain why Einstein gravity has to be modified at galactic scales according to Verlinde, and how the universal acceleration scale which appears in rotation curves naturally arises from an entropic argument. Moreover, I will discuss Verlinde's formula for the extra dark gravitational force which, he argues, makes dark matter obsolete at galactic scales. My talk will be quite basic, with not many formulas, so I expect lots of questions!



  • 15.30 - 16.00, H320

    Takahiro Ueda (Nikhef)
    Perturbative QCD at four and five loops

    Abstract: In recent years, physics programmes of the LHC have become more and more precise. For some processes even the next-to-next-to-next-to-leading (N^3LO) corrections to partonic cross sections in perturbative QCD are now available. However, in principle N^3LO analyses need parton distributions evolved with four-loop splitting functions, which are still unknown. Motivated by this, we developed Forcer, a FORM program for analytically calculating four-loop massless propagator-type Feynman integrals. In this talk, the status of calculations of the four-loop splitting functions will be presented. I will also discuss five-loop physics results obtained by Forcer with local R^*-operations.



  • 16.00 Nikhef "Science Cafe", including borrel
    This is not a HPP activity, but you are welcome to join.
    Speakers (giving 10 minute presentations) are:
    - Elena Petreska (Theoretical Physics), Title: What are protons and nuclei made of?
    - Sean Benson (LHCb) Title: New discoveries with real-time analysis