HEP Theory Seminars SS 16

Thu 14.04.2016, 16.30 h

L. Lopez Honorez (Brüssel)

Dark matter annihilations and 21cm signal

Dark matter (DM) annihilations into charged particles change the thermal history of the Universe and, as a consequence, affect the 21 cm signal. In my talk I will discuss how predicting the effect of DM strongly relies on the modeling of annihilations inside halos. Given current uncertainties on the description of the astrophysical processes driving the epochs of reionization, X-ray heating and Lyman-α pumping, we found in a recent work that disentangling DM signatures from purely astrophysical effects, related to early-time star formation processes or late-time galaxy X-ray emissions, will be a challenging task. We have concluded that only annihilations of DM particles with masses of ∼100 MeV, could leave an unambiguous imprint on the 21 cm signal and, in particular, on the 21 cm power spectrum. Additional measurements of the 21 cm signal at different cosmic epochs should help to break the strong parameter degeneracies between DM annihilations and astrophysical effects in order to undoubtedly single out a DM imprint for masses different from ∼100 MeV.


Thu 21.04.2016, 16.30 h

C. Schwinn (RWTH)

Precise predictions for squark and gluino production at the LHC


Thu 28.04.2016, 16.30 h

C. Degrande (Durham)

Automated BSM at NLO

After an introduction of the tools that have been developed to automate the study of BSM at NLO, I will discuss two examples : charged Higgs production and gluino pair production.


Thu 12.05.2016, 16.30 h

B. Garbrecht (TU München)


With the discovery of neutrino mixing and oscillations, leptogenesis became one of the most plausible scenarios for explaining the matter-antimatter asymmetry of the Universe because the observed neutrino mass parameters happen to roughly agree with the values that are preferred by leptogenesis. I will explain the standard scenario for leptogenesis in the strong washout regime as well as popular variants and refinements such as the resonant scenario and effects from the mixing of active lepton flavours. Further, I will discuss leptogenesis from oscillations of hypothetical GeV scale sterile neutrinos, which are among the search targets of current and proposed high-luminosity experiments.


Thu 02.06.2016, 16.30 h

M. Worek (RWTH)

Precision predictions for top quark pair production in association with a jet at the LHC

I will discuss top quark pair production in association with a jet in the di-lepton channel at NLO in QCD. First I will discuss theoretical status for this process and afterwords I will describe NLO QCD corrections to this process with complete off-shell effects. Such calculations include all non-resonant diagrams, interferences and off-shell effects of the top quark. Moreover, non-resonant and off-shell effects due to the finite W gauge boson width are taken into account. This calculation constitutes the first fully realistic NLO computation for top quark pair production with a final state jet in hadronic collisions. I will also present numerical results for differential distributions as well as total cross sections  for the LHC at 8 TeV and 13 TeV.


Thu 09.06.2016, 16.30 h

F. Donato (Turin)

Antimatter in the Galaxy: Open problems for fundamental physics

The physics of the galactic cosmic rays is entering a precision era, which touches also the rare species as the cosmic antimatter.  We show how the interpretation of antiproton data by recent experiments, mostly by AMS-02,
starts to be limited by the lack of data on the relevant cross sections. In particular, all the reactions occurring in the Galaxy between hydrogen and helium whether are not sufficiently accurate, or are lacking at all. We discuss at which extent  the models for galactic cosmic ray data - including also a viable dark matter component - could improve with dedicated experiments at colliders. We finally inspect the effect of close sources - such as supernovae and pulsars - on the positron and electron fluxes measured by AMS-02.


Thu 16.06.2016, 16.30 h

O.  Philipsen (Frankfurt)

Towards the QCD phase diagram for hot and dense QCD

The physics of matter at finite and large baryon densities plays an imortant role for the astrophysics of compact stars as well as for heavy ion collisions or the description of nuclear matter. Because of the so-called sign problem of the quark determinant, lattice QCD cannot be simulated at finite baryon densities. I review techniques to work around that problem and summarize our knowledge of the QCD phase diagram.


Thu 14.07.2016, 16.30 h

J. Schaffner-Bielich (Frankfurt)

Compact Stars: Neutron Stars or Quark Stars?

The recent measurement of two solar mass pulsars has put stringent constraints on the properties of neutron star matter. The questions arises whether or not exotic phases or a first order phase transition in the core of neutron stars are still compatible with the new pulsar mass constraint. In addition the equation of state of neutron stars can be constrained at high densities by perturbative QCD with implications for the mass-radius relation of neutron stars. The possible existence of pure quark stars which are bound by gravity only will be also discussed in the presentation.