Adrian Ghinculov

Massive two--loop diagrams : The Higgs propagator

Abstract Formulae are provided to express any two-loop scalar integral with arbitrary masses and arbitrary external momenta in terms of an integral of one fairly simple function or of its derivatives. Such integrals can be calculated numerically with high precision. Good agreement is found with known analytical expressions of specific two-loop diagrams. To prove the effectiveness of these techniques, the two-loop self-energy of the Higgs boson to order ( g 2 M 2 H / m 2 w ) 2 is calculated, and the correctness of the result is checked by using the unitarity of the S -matrix. This result allows one to disentangle the leading correction to the location of the Higgs resonance in fermion scattering, and to derive a perturbative bound of ∼1.2 TeV on the mass of the Higgs boson.

Massive two-loop integrals in renormalizable theories

We propose a framework for calculating two-loop Feynman diagrams which appear within a renormalizable theory in the general mass case and at finite external momenta. Our approach is a combination of analytical results and of high accuracy numerical integration, similar to a method proposed previously [A. Ghinculov and J.J. van der Bij, Nucl. Phys. B 436 (1995) 30] for treating diagrams without numerators. We reduce all possible tensor structures to a small set of scalar integrals, for which we provide integral representations in terms of four basic functions. The algebraic part is suitable for implementing in a computer program for the automatic generation and evaluation of Feynman graphs. The numerical part is essentially the same as in the case of Feynman diagrams without numerators.

Two-loop heavy Higgs correction to Higgs decay into vector bosons

Abstract The leading m H radiative correction to the Higgs decay width into a pair of weak vector bosons is calculated at the two-loop level, using the equivalence theorem in Landau gauge. The result indicates the breakdown of perturbation theory if the Higgs boson is heavier than ∼ 930 GeV, in spite of the smallness of the one-loop radiative correction.

Two-loop heavy Higgs corrections to the Higgs fermionic width

Abstract We calculate the two-loop electroweak corrections to the fermionic decay width of the Higgs boson at leading order in m H . The sum of one-loop and two-loop radiative corrections turns out to be at the 6% level over the whole range of m H where the perturbation theory is supposed to be a sensible approximation. We show that the perturbative approach breaks down at m H ∼1.4 TeV, and address the question of its relevance beyond this limit.

THE HIGGS RESONANCE SHAPE IN GLUON FUSION: HEAVY HIGGS EFFECTS

We study the influence of two-loop radiative corrections of enhanced electroweak strength on Higgs production at the LHC. We consider Higgs production by the gluon fusion mechanism, with the subsequent decay of the Higgs boson into a pair of Z bosons, and incorporate the resonance shape corrections up to the order (g2mH2/mW2)2. We take into account the full gg → ZZ process and the qq → ZZ background, as well as the subsequent decay of the Z pair into leptons. We also discuss the theoretical uncertainty related to the use of the equivalence theorem in this process.

Position of a heavy Higgs pole

Abstract Higher loop calculations in the Higgs sector of the standard model at the Higgs mass scale have shown that perturbation theory diverges very badly at about 1 TeV in the on-shell renormalization scheme. The prediction of the position of the Higgs pole in the complex s plane becomes unreliable. We show that in the pole renormalization scheme this appears to have much better convergence properties, while showing good agreement with the on-shell scheme over the validity range of the latter. This suggests that the pole scheme should be preferable for phenomenological studies of heavy Higgs bosons. We discuss whether this behaviour can be the result of a certain relation between the on-shell mass and the pole mass at the nonperturbative level.

Radiative corrections to the lineshape of a heavy Higgs boson at muon colliders

We study the next to next to leading order radiative corrections of enhanced electroweak strength to the lineshape of the Higgs boson in the processes

NLO correction to Higgs boson parameters in the 1/N expansion

{ensuremath{mu}}^{+}{ensuremath{mu}}^{ensuremath{-}}ensuremath{rightarrow}Hensuremath{rightarrow}mathrm{ZZ}

Nonperturbative Higgs propagator: NLO correction in the 1/N expansion

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On the evaluation of three-loop scalar integrals in the massive case☆

{ensuremath{mu}}^{+}{ensuremath{mu}}^{ensuremath{-}}ensuremath{rightarrow}Hensuremath{rightarrow}toverline{t}