HEP Theorie-Seminare WS 14/15

Do. 29.01.2015, 17.00 Uhr

S. Badger (CERN)

Multi-Loop Integrand Reduction Techniques

Abstract:
I will discuss recent progress in developing algebraic reduction methods extending the well known OPP formalism at one-loop. I will describe the application to the two-loop five-gluon amplitude with all helicities positive.

 

Do. 22.01.2015, 17.00 Uhr

S. Kraml (Grenoble)

Implications of the 125 GeV Higgs boson for new physics

 

Do. 15.01.2015, 17.00 Uhr

N. Beisert (ETH Zürich)

Smooth Wilson Loops in N=4 Superspace and Yangian Symmetry

 

Do. 11.12.2014, 17.00 Uhr

M. Pellen (RWTH)

Supersymmetry: from the algebra to NLO LHC phenomenology

 

Do. 04.12.2014, 17.00 Uhr

D. Rathlev (Uni Zürich)

Diboson production in NNLO QCD

Abstract:
I will report on our recent progress on computing the NNLO QCD corrections to diboson production at the LHC. I will describe the qT subtraction method used in the calculation and its origins in the formalism of qT resummation in some detail. The discussion of phenomenological results will put a particular emphasis on the excess in the WW cross section measurements at the LHC.

 

Do. 27.11.2014, 17.00 Uhr

T. Kasemets (NIKHEF Amsterdam)

Transverse momentum dependent (un)polarized gluon distributions in Higgs production

Abstract:
We discuss transverse momentum dependent (un)polarized gluon distributions (gluon TMDs) and their proper definitions in the context of factorization theorems. All the gluon TMDs have a scale evolution driven by a universal evolution kernel which is resummed to NNLL. Through an explicit NLO calculation of unpolarized and linearly polarized gluon TMDs we demonstrate that they are free from rapidity divergences, and calculate the Wilson coefficients of their expansion in terms of the (collinear) parton distribution functions. We investigate the effect of the linearly polarized gluons on the transverse momentum spectrum of the Higgs boson and compare with data.

 

Do. 20.11.2014, 16.00 Uhr !!!

C. Anastasiou (ETH Zürich)

Higgs production at N3LO beyond the threshold approximation

Abstract: 
Higgs boson signals provide stringent tests of the Standard Model and they are excellent probes of new physics.  The inclusive cross-section for Higgs production is an important input for these studies. I will talk about the calculation of the cross-section at N3LO in perturbative QCD, the mathematical methods used in order to break the NNLO barrier for hadron collider observables, the calculation of the cross-section at N3LO in the threshold limit and recent work to calculate the cross-section beyond that limit.  Finally, I will make a critical appraisal of the threshold approximation and the precision that can be achieved with the complete N3LO correction.

 

 

Do. 13.11.2014, 17.00 Uhr

B. Hartanto (RWTH)

Hard-photon production with b jets at hadron colliders

 

Do. 06.11.2014, 17.00 Uhr

E. Re (Oxford)

Towards NNLO Event Generators for the LHC

Abstract:
Monte Carlo event generators are used extensively in many LHC searches. I will briefly explain the basic concepts and approximations upon which these tools are built and review the theoretical developments that in the last decade allowed to improve substantially the accuracy of these programs. I will then explain how a combination of two of these methods (POWHEG and MiNLO) allows to match parton showers with NNLO computations, and show recent results for Higgs and Drell-Yan production.

 

Do. 30.10.2014, 17.00 Uhr

D. Gonçalves Netto (Durham)

Mass Effects in the Higgs-Gluon Coupling: Boosted vs Off-Shell Production

Abstract:
In the upcoming LHC run we will be able to probe the structure of the loop-induced Higgs-gluon coupling through kinematics. First, we establish state-of-the-art simulations with up to two jets to next-to-leading order including top mass effects. They allow us to search for deviations from the low-energy limits in boosted Higgs production. In addition, the size of the top mass effects suggests that they should generally be included in Higgs studies at the LHC. Next, we show how off-shell Higgs production with a decay to four leptons is sensitive to the same top mass effects. We compare the potential of both methods based on the same top-Higgs Lagrangian. Finally, we comment on related model assumptions required for a Higgs width measurement.

 

Do. 23.10.2014, 17.00 Uhr

M. Garny (CERN)

Dark matter with t-channel mediators

Abstract:
From the experimental point of view, two of the most profound reasons to search for physics beyond the Standard Model come from cosmological observations: the baryon asymmetry and dark matter. In this talk we discuss the interplay of indirect, direct and collider searches for WIMP dark matter that interacts with the Standard Model fermions via a t-channel mediator. When the mediator is close in mass to the Majorana dark matter particle (similar to the coannihilation region in the MSSM), a spectral feature in the gamma ray flux from internal bremsstrahlung gives a very characteristic signature that can be searched for in future observatories like CTA. For somewhat larger mass splitting, LHC searches for jets and missing energy yield the strongest constraints. We also discuss the relevance of taking the mediator into account.