arXiv subjects

Pier Paolo Giardino

Publications and source records attributed to Pier Paolo Giardino.

44 records · Page 3Linked to original sources

arXiv2016

On the two-loop virtual QCD corrections to Higgs boson pair production in the Standard Model

We compute the next-to-leading order virtual QCD corrections to Higgs pair production via gluon fusion. We present analytic results for the two-loop contributions to the spin-0 and spin-2 form factors in the amplitude. The reducible contributions, given by the double-triangle diagrams, are evaluated exactly while the two-loop irreducible diagrams are evaluated by an asymptotic expansion in heavy top quark mass up to and including terms of $\mathcal{O}(1/m_t^8)$. Assuming that the finite top-quark mass effects are of similar size in the entire range of partonic energies we estimate that mass effects can reduce the hadronic cross section by at most $10\%$.

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arXiv2014

The $m_{\scriptscriptstyle W}-m_{\scriptscriptstyle Z}$ interdependence in the Standard Model: a new scrutiny

The $m_{\scriptscriptstyle W}-m_{\scriptscriptstyle Z}$ interdependence in the Standard Model is studied at $O(α^2) $ in the $\overline{MS}$ scheme. The relevant radiative parameters, $Δ\hatα (μ),\, Δ\hat{r}_{W},\, \hatρ$ are computed at the full two-loop level augmented by higher-order QCD contributions and by resummation of reducible contributions. We obtain $m_{\scriptscriptstyle W} = 80.357 \pm 0.009 \pm 0.003$ GeV where the errors refer to the parametric and theoretical uncertainties, respectively. A comparison with the known result in the On-Shell scheme gives a difference of $ \approx 6$ MeV. As a byproduct of our calculation we also obtain the $\overline{MS}$ electromagnetic coupling and the Weinberg angle at the top mass scale, $\hatα (M_t) = (127.73)^{-1} \pm 0.0000003$ and $\sin^{2}\!\hatθ_{W} (M_t) = 0.23462 \pm 0.00012$.

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arXiv2014

Investigating the near-criticality of the Higgs boson

We extract from data the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.

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arXiv2014

The universal Higgs fit

We perform a state-of-the-art global fit to all Higgs data. We synthesise them into a 'universal' form, which allows to easily test any desired model. We apply the proposed methodology to extract from data the Higgs branching ratios, production cross sections, couplings and to analyse composite Higgs models, models with extra Higgs doublets, supersymmetry, extra particles in the loops, anomalous top couplings, invisible Higgs decay into Dark Matter. Best fit regions lie around the Standard Model predictions and are well approximated by our 'universal' fit. Latest data exclude the dilaton as an alternative to the Higgs, and disfavour fits with negative Yukawa couplings. We derive for the first time the SM Higgs boson mass from the measured rates, rather than from the peak positions, obtaining $M_h = 125.0 \pm 1.8$ GeV.

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arXiv2012

Is the resonance at 125 GeV the Higgs boson?

The recently discovered resonance at 125 GeV has properties remarkably close to those of the Standard Model Higgs boson. We perform model-independent fits of all presently available data. The non- standard best-fits found in our previous analyses remain favored with respect to the SM fit, mainly but not only because the γγ rate remains above the SM prediction.

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arXiv2012

Reconstructing Higgs boson properties from the LHC and Tevatron data

We perform a phenomenological fit to all ATLAS, CMS, CDF and D0 Higgs boson data available after Moriond 2012. We allow all Higgs boson branching fractions, its couplings to standard model particles, as well as to an hypothetical invisible sector to vary freely, and determine their current favourite values. The standard model Higgs boson with a mass 125 GeV correctly predicts the average observed rate and provides an acceptable global fit to data. However, better fits are obtained by non-standard scenarios that reproduce anomalies in the present data (more γγ and less WW signals than expected), such as modified rates of loop processes or partial fermiophobia. We find that present data disfavours Higgs boson invisible decays. We consider implications for the standard model, for supersymmetric and fermiophobic Higgs bosons, for dark matter models, for warped extra-dimensions.

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arXiv2011

Threshold corrections to hard supersymmetric relations

We compute the one-loop threshold corrections to hard supersymmetric relations involving gauge and gaugino couplings for the case of a Split-SUSY-like spectrum with moderate splitting. We show that these contributions are small, however in principle they will typically have to be taken into account if the heavy scalar sector is below 100 TeV and if one reaches, at future linear colliders, the precision that is necessary to perform this kind of measurements.

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arXiv2011

LHC bounds on large extra dimensions

We derive new dominant bounds on the coefficient of the effective operator generated by tree-level graviton exchange in large extra dimensions from pp \rightarrow jj data at LHC: M_T > 2.1TeV (ATLAS after 3.1/pb of integrated luminosity), M_T > 3.4 TeV (CMS after 36/pb), MT > 3.2 TeV (ATLAS after 36/pb). We clarify the role of on-shell graviton exchange and compare the full graviton amplitude to ATLAS data, setting bounds on the fundamental quantum-gravity scale.

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