Higgs Pair Production Cross Section Research Articles

High-energy expansion of two-loop massive four-point diagrams

We apply the method of regions to the massive two-loop integrals appearing in the Higgs pair production cross section at the next-to-leading order, in the high energy limit. For the non-planar integrals, a subtle problem arises because of the indefinite sign of the second Symanzik polynomial. We solve this problem by performing an analytic continuation of the Mandelstam variables such that the second Symanzik polynomial has a definite sign. Furthermore, we formulate the procedure of applying the method of regions systematically. As a by-product of the analytic continuation of the Mandelstam variables, we obtain crossing relations between integrals in a simple and systematic way. In our formulation, a concept of “template integral” is introduced, which represents and controls the contribution of each region. All of the template integrals needed in the computation of the Higgs pair production at the next-to-leading order are given explicitly. We also develop techniques to solve Mellin-Barnes integrals, and show them in detail. Although most of the calculation is shown for the concrete example of the Higgs pair production process, the application to other similar processes is straightforward, and we anticipate that our method can be useful also for other cases.

Higgs Pair Production as a Signal of Enhanced Yukawa Couplings.

We present a nontrivial correlation between the enhancement of the Higgs-fermion couplings and the Higgs pair production cross section in two Higgs doublet models with a flavor symmetry, with implications for LHC searches. This symmetry suppresses flavor-changing neutral couplings of the Higgs boson and allows for a partial explanation of the hierarchy in the Yukawa sector. After taking into account the constraints from electroweak precision measurements, Higgs coupling strength measurements, and unitarity and perturbativity bounds, we identify an interesting region of parameter space leading to enhanced Yukawa couplings as well as enhanced di-Higgs gluon fusion production at the LHC reach. This effect is visible in both the resonant and nonresonant contributions to the Higgs pair production cross section. We encourage dedicated searches based on differential distributions as a novel way to indirectly probe enhanced Higgs couplings to light fermions.

Corrections to di-Higgs boson production with light stops and modified Higgs couplings

The Higgs pair production in gluon fusion is a sensitive probe of beyond-standard model (BSM) phenomena and its detection is a major goal for the LHC and higher energy hadron collider experiments. In this work we reanalyze the possible modifications of the Higgs pair production cross section within low energy supersymmetry models. We show that the supersymmetric contributions to the Higgs pair production cross section are strongly correlated with the ones of the single Higgs production in the gluon fusion channel. Motivated by the analysis of ATLAS and CMS Higgs production data, we show that the scalar superpartners' contributions may lead to significant modification of the di-Higgs production rate and invariant mass distribution with respect to the SM predictions. We also analyze the combined effects on the di-Higgs production rate of a modification of the Higgs trilinear and top-quark Yukawa couplings in the presence of light stops. In particular, we show that due to the destructive interference of the triangle and box amplitude contributions to the di-Higgs production cross section, even a small modification of the top-quark Yukawa coupling can lead to a significant increase of the di-Higgs production rate.

The CP-violating 2HDM in light of a strong first order electroweak phase transition and implications for Higgs pair production

We investigate the strength of the electroweak phase transition (EWPT) within the CP-violating 2-Higgs-Doublet Model (C2HDM). The 2HDM is a simple and well-studied model, which can feature CP violation at tree level in its extended scalar sector. This makes it, in contrast to the Standard Model (SM), a promising candidate for explaining the baryon asymmetry of the universe through electroweak baryogenesis. We apply a renormalisation scheme which allows efficient scans of the C2HDM parameter space by using the loop-corrected masses and mixing matrix as input parameters. This procedure enables us to investigate the possibility of a strong first order EWPT required for baryogenesis and study its phenomenological implications for the LHC. Like in the CP-conserving (real) 2HDM (R2HDM) we find that a strong EWPT favours mass gaps between the non-SM-like Higgs bosons. These lead to prominent final states comprised of gauge+Higgs bosons or pairs of Higgs bosons. In contrast to the R2HDM, the CP-mixing of the C2HDM also favours approximately mass degenerate spectra with dominant decays into SM particles. The requirement of a strong EWPT further allows us to distinguish the C2HDM from the R2HDM using the signal strengths of the SM-like Higgs boson. We additionally find that a strong EWPT requires an enhancement of the SM-like trilinear Higgs coupling at next-to-leading order (NLO) by up to a factor of 2.4 compared to the NLO SM coupling, establishing another link between cosmology and collider phenomenology. We provide several C2HDM benchmark scenarios compatible with a strong EWPT and all experimental and theoretical constraints. We include the dominant branching ratios of the non-SM-like Higgs bosons as well as the Higgs pair production cross section of the SM-like Higgs boson for every benchmark point. The pair production cross sections can be substantially enhanced compared to the SM and could be observable at the high-luminosity LHC, allowing access to the trilinear Higgs couplings.

Higgs pair production: choosing benchmarks with cluster analysis

New physics theories often depend on a large number of free parameters. The precise values of those parameters in some cases drastically affect the resulting phenomenology of fundamental physics processes, while in others finite variations can leave it basically invariant at the level of detail experimentally accessible. When designing a strategy for the analysis of experimental data in the search for a signal predicted by a new physics model, it appears advantageous to categorize the parameter space describing the model according to the corresponding kinematical features of the final state. A multi-dimensional test statistic can be used to gauge the degree of similarity in the kinematics of different models; a clustering algorithm using that metric may then allow the division of the space into homogeneous regions, each of which can be successfully represented by a benchmark point. Searches targeting those benchmark points are then guaranteed to be sensitive to a large area of the parameter space. In this document we show a practical implementation of the above strategy for the study of non-resonant production of Higgs boson pairs in the context of extensions of the standard model with anomalous couplings of the Higgs bosons. A non-standard value of those couplings may significantly enhance the Higgs pair production cross section, such that the process could be detectable with the data that the Large Hadron Collider will collect in Run 2.

LIGHT LEPTOQUARKS AND HIGGS PAIR PRODUCTION

The data collected by the LHC experiments at 7 and 8 TeV with ~5 and 20fb-1 respectively is refining the details of the Higgs like resonances found last year [1,2]. Many decay channels have been searched for and the individual channels so far have given us a consistent picture with what one expects from the SM Higgs. On the other hand, the self interaction of the Higgs, which is probed by the Higgs pair production [3-7], is too feeble in the SM to be detected with these early data set. Even at 14 TeV run, the luminosity required for probing this process is very high [7-17]. This fact, namely the smallness of the corresponding Higgs pair production cross-section, makes it sensitive to a presence of a new physics [18-31]. In particular, relatively light colored particles are known to affect the cross-section substantially [18-22]. As a mater of fact there are many models with various motivations including models of GUT remnants [32-39], composite models [40-48] or a radiative neutrino mass models [49-51] which may give such contributions. Among these the scalars are interesting as they may play crucial role in the spontaneous symmetry breaking through additional terms with large portal couplings in the scalar potential. In the present work we study the phenomenological consequences of the Standard Model extension by two or more colored scalar particles. As a case study we take several leptoquarks (LQ) since there is an active experimental program by both ATLAS and CMS [52-57] and the lower bounds on their masses have now reached impressive levels some as high as a TeV value. On the other hand simultaneous presence of several LQs, may open up additional channels and therefore weakens these bounds. Specific models where the LQs are introduced to explain a certain phenomenon usually requires more than one LQs as in the model we study here. I examine a possibility of the existence of LQs with masses as light as ~180 GeV and study their effect for the single and di Higgs productions. As we will see the Higgs pair production is substantially altered in the low mass range below 300 GeV without too much change in the Higss diphoton decay channel if portal couplings are large. These couplings are required to have opposite signs by the latest Higgs data or small in magnitude. The model I consider has two LQs, an SU(2) doublet ω and a singlet χ. As we will see their simultaneous presence still allows them to have relatively light masses and escape the current bounds. In particular, the current bounds do not include LQs decaying to τt the masses below 200 GeV. Such a scenario, for example, has appeared in a model considered by Babu and Julio [49], where the light neutrino masses are induced by two-loop effects from LQs. If their masses are only of order few hundred GeV, as it is required in this case, the scenario can be probed or even excluded with the data from the LHC. Therefore this is one of the easiest model which can be tested and is the subject of the current study. Although I consider a particular model, it should be stressed that other models with colored particles can affect the pair productions in a similar manner.In Section II, I briefly list the current experimental status on the Higgs production and decay rates. Then I introduce the model I examined in the paper. Section III contains main part of this work where the numerical results for the single and pair Higgs productions are presented. The conclusion is given in Section IV.

Hidden sector effects on double Higgs production near threshold at the LHC

In this Letter we study a novel effect of a hidden sector coupling to the standard model Higgs boson: an enhancement of the Higgs pair production cross section near threshold due to bound state effects. After summing the ladder contributions of the hidden sector to the effective ggHH coupling, we find the amplitude for gluon–gluon scattering via a Higgs loop. We relate this amplitude to the double Higgs production cross section via the optical theorem. We find that enhancements of the O(100) for the partonic cross section near the threshold region can be obtained for a hidden sector strongly coupled to the Higgs boson. The corresponding cross section at the LHC can be as large as O(10) times the SM result for extreme values of the coupling. The detection of such an effect could in principle lead to important information about the hidden sector.

Higgs pair production at the LHC in models with universal extra dimensions

In this Letter we study the process of gluon fusion into a pair of Higgs bosons in a model with one universal extra dimension. We find that the contributions from the extra top quark Kaluza–Klein excitations lead to a Higgs pair production cross section at the LHC that can be significantly altered compared to the Standard Model value for small values of the compactification scale.