Adrian Ghinculov
University of Freiburg
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Featured researches published by Adrian Ghinculov.
Nuclear Physics | 1995
Adrian Ghinculov; J.J. van der Bij
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.
Nuclear Physics | 1998
Adrian Ghinculov; York-Peng Yao
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.
Nuclear Physics | 1995
Adrian Ghinculov
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.
Physics Letters B | 1994
Adrian Ghinculov
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.
Nuclear Physics | 1996
Adrian Ghinculov; J.J. van der Bij
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.
Physics Letters B | 1997
Adrian Ghinculov; Thomas Binoth
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.
Physical Review D | 1997
Thomas Binoth; Adrian Ghinculov
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
Physics Letters B | 1998
Thomas Binoth; Adrian Ghinculov; J.J. van der Bij
{ensuremath{mu}}^{+}{ensuremath{mu}}^{ensuremath{-}}ensuremath{rightarrow}Hensuremath{rightarrow}mathrm{ZZ}
Physical Review D | 1998
Adrian Ghinculov; Thomas Binoth; J.J. van der Bij
and
Physics Letters B | 1996
Adrian Ghinculov
{ensuremath{mu}}^{+}{ensuremath{mu}}^{ensuremath{-}}ensuremath{rightarrow}Hensuremath{rightarrow}toverline{t}