S. Alekhin

The top quark and Higgs boson masses and the stability of the electroweak vacuum

Abstract The ATLAS and CMS experiments observed a particle at the LHC with a mass ≈ 126 GeV , which is compatible with the Higgs boson of the Standard Model. A crucial question is, if for such a Higgs mass value, one could extrapolate the model up to high scales while keeping the minimum of the scalar potential that breaks the electroweak symmetry stable. Vacuum stability requires indeed the Higgs boson mass to be M H ≳ 129 ± 1 GeV , but the precise value depends critically on the input top quark pole mass which is usually taken to be the one measured at the Tevatron, m t exp = 173.2 ± 0.9 GeV . However, for an unambiguous and theoretically well-defined determination of the top quark mass one should rather use the total cross section for top quark pair production at hadron colliders. Confronting the latest predictions of the inclusive p p ¯ → t t ¯ + X cross section up to next-to-next-to-leading order in QCD to the experimental measurement at the Tevatron, we determine the running mass in the MS ¯ -scheme to be m t MS ¯ ( m t ) = 163.3 ± 2.7 GeV which gives a top quark pole mass of m t pole = 173.3 ± 2.8 GeV . This leads to the vacuum stability constraint M H ⩾ 129.4 ± 5.6 GeV to which a ≈ 126 GeV Higgs boson complies as the uncertainty is large. A very precise assessment of the stability of the electroweak vacuum can only be made at a future high-energy electron–positron collider, where the top quark pole mass could be determined with a few hundred MeV accuracy.

Mellin Representation for the Heavy Flavor Contributions to Deep Inelastic Structure Functions

We derive semi–analytic expressions for the analytic continuation of the Mellin transforms of the heavy flavor QCD coefficient functions for neutral current deep inelastic scattering in leading and next-to-leading order to complex values of the Mellin variable N. These representations are used in Mellin–space QCD evolution programs to provide fast evaluations of the heavy flavor contributions to the structure functions F2(x,Q 2 ),FL(x,Q 2 ) and g1(x,Q 2 ).

Precise charm-quark mass from deep-inelastic scattering

Abstract We present a determination of the charm-quark mass in the MS ¯ scheme using the data combination of charm production cross section measurements in deep-inelastic scattering at HERA. The framework of global analyses of the proton structure accounts for all correlations of the charm-quark mass with the other non-perturbative parameters, most importantly the gluon distribution function in the proton and the strong coupling constant α s ( M Z ) . We obtain at next-to-leading order in QCD the value m c ( m c ) = 1.15 ± 0.04 ( exp ) − 0.00 + 0.04 ( scale ) GeV and at approximate next-to-next-to-leading order m c ( m c ) = 1.24 ± 0.03 ( exp ) − 0.02 + 0.03 ( scale ) − 0.07 + 0.00 ( theory ) GeV with an accuracy competitive with other methods.

Parton distribution functions,

We determine a new set of parton distribution functions (ABMP16), the strong coupling constant

\alpha_s

\alpha_s

, and heavy-quark masses for LHC Run II

and the quark masses

NNLO benchmarks for gauge and Higgs boson production at TeV hadron colliders

m_c

Higher-order constraints on the Higgs production rate from fixed-target DIS data

,

Determination of strange sea distributions from νN deep inelastic scattering

m_b

Update of the NNLO PDFs in the 3-, 4-, and 5-flavour scheme

and