Are bottom PDFs needed at the LHC?
  Processes involving bottom quarks play a crucial role in the LHC phenomenology, from flavour physics to Higgs characterisation and as a window to new physics, appearing both as signals and irreducible background in BSM searches. These processes can be described in QCD either in a 4-flavor or 5-flavor scheme. In the former, $b$ quarks appear only in the final state and are considered massive. In 5-flavor schemes, calculations include $b$ quarks in the initial state. Possibly large logarithms originating from the collinear splitting of gluons into bottom pairs are resummed into the $b$ parton distribution function (PDF). In this contribution, I describe a simple method to assess the size of the logarithms in processes initiated by bottom quarks and show how a substantial and justified agreement between calculations in the two schemes can be achieved. As a consequence both calculations can be used in different context. To conclude, an overview of the current studies aiming to generalise the current appraisal is given and some preliminary results are discussed. 
Maria Ubiali
hep-ph