Search

The quest for new heavy states is a critical component of the LHC physics program. In this letter, we study the search for pseudoscalar bosons produced in association with a $t\bar{t}$ pair. We consider the final state $t\bar{t} A \to t\bar{t} b\bar{b}$ with di-leptonic top pair signature, and reconstruct the boosted $A \to b\bar{b}$ candidate with jet substructure techniques, achieving a remarkable sensitivity over a broad range of pseudoscalar masses and Yukawa couplings. We apply this strategy to a Type-I Two-Higgs-Doublet Model, demonstrating its ability to probe a realistic, UV-complete extended Higgs sector. In particular, we find that the $13~TeV$ LHC with $300~fb^{-1}$ of data can constrain the region $\tan\beta>1.5$ at 95$\%$ CL for a light pseudoscalar with $m_A = 50$ GeV. Moreover, the whole mass range $20~GeV, Comment: 10 pages, 7 figures, 4 tables

Effective Lagrangians are a useful tool for a data-driven approach to physics beyond the Standard Model at the LHC. However, for the new physics scales accessible at the LHC, the effective operator expansion is only relatively slowly converging at best. For tree-level processes, it has been found that the agreement between the effective Lagrangian and a range of UV-complete models depends sensitively on the appropriate definition of the matching. We extend this analysis to the one-loop level, which is relevant for electroweak precision data and Higgs decay to photons. We show that near the scale of electroweak symmetry breaking the validity of the effective theory description can be systematically improved through an appropriate matching procedure. In particular, we find a significant increase in accuracy when including suitable terms suppressed by the Higgs vacuum expectation value in the matching., no appendix

With the LHC close to complete its 8 TeV run, the experimental searches have already started to probe the vast beyond-the-standard Model scenery. Providing next-to-leading order (NLO) predictions for the major new physics discovery channels is therefore a most pressing request to particle phenomenologists these days. MadGolem is a new computational tool that automates NLO calculations of generic 2->2 new physics processes in the MadGraph/Golem framework. In this contribution we concisely describe the structure and performance of the code, with particular focus on the generation of the renormalized one-loop amplitudes and the automatized subtraction of infrared and on-shell divergences. We briefly survey the many dedicated tests of all these aspects and outline some applications to LHC phenomenology., Prepared for the proceedings to Loops and Legs in Quantum Field Theory - 11th DESY Workshop on Elementary Particle Physics, April 15-20, 2012, Wernigerode, Germany

We review selected results for Higgs boson production at Linear Colliders in the framework of the general Two-Higgs-Doublet Model (2HDM). We concentrate on the analysis of i) the pairwise production of neutral Higgs bosons (hA,HA); and ii) the neutral Higgs boson-strahlung modes (hZ, HZ). We identify sizable production rates, in the range of 10-100 fb for center-of-mass energies of 0.5 TeV, alongside with large quantum effects (up to 50 %), which we can fundamentally track down to the enhancement power of the triple-Higgs self-interactions. This constitutes a telltale signature of the 2HDM, with no counterpart in e.g. the Minimal Supersymmetric Standard Model (MSSM). We compare these results with several complementary double and triple Higgs-boson production mechanisms at order O(\alpha^3_{ew})-O(\alpha^4_{ew} and spotlight a characteristic phenomenological profile which could eventually be highly distinctive of a non-supersymmetric two-Higgs-doublet structure., Comment: 8 pages, 4 figures, 2 tables. Prepared for the proceedings of the 3rd LC-Forum meeting, 7-9 February 2012, DESY, Hamburg

We consider the loop-induced production of a single Higgs boson from direct photon-photon scattering at a photon collider. A dedicated analysis of the total cross section and the relative strength of the effective $h\gamma\gamma$ coupling is carried out within the general Two-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric Standard Model (MSSM). We systematically survey representative regions over the parameter space, in full agreement with brought-to-date theoretical and phenomenological restrictions, and obtain production rates up to $10^4$ Higgs boson events per $500 fb^{-1}$ of integrated luminosity. We identify trademark phenomenological profiles for the different $\gamma\gamma \to h$ channels and trace them back to the distinctive dynamical features characterizing each of these models -- most significantly, the enhancement potential of the Higgs self-interactions in the general 2HDM. The upshot of our results illustrates the possibilities of $\gamma\gamma$-physics and emphasizes the relevance of linear colliders for the Higgs boson research program., Comment: LaTeX, 9 pages, 2 Figures, prepared for the proceedings to the workshop Linear Collider 2011: Understanding QCD at Linear Colliders in searching for old and new physics, 12-16 September 2011, ECT*, Trento, Italy

We present an updated overview on the phenomenology of one-loop Higgs boson production at Linear Colliders within the general Two-Higgs-Doublet Model (2HDM). First we report on the Higgs boson pair production, and associated Higgs-Z boson production, at O(alpha^3_{ew}) from e+e- collisions. These channels furnish cross-sections in the range of 10-100 fb for Ecm=0.5 TeV and exhibit potentially large radiative corrections (of order 50%), whose origin can be traced back to the genuine enhancement capabilities of the triple Higgs boson self-interactions. Next we consider the loop-induced production of a single Higgs boson from direct gamma-gamma scattering. We single out sizable departures from the corresponding rates in the Standard Model, which are again correlated to trademark dynamical features of the 2HDM -- namely the balance of the non-standard Higgs/gauge, Higgs/fermion and Higgs self-interactions leading to sizable (destructive) interference effects. This pattern of quantum effects is unmatched in the MSSM, and could hence provide distinctive footprints of non-supersymmetric Higgs boson physics. Both calculations are revisited within a common, brought-to-date framework and include, in particular, the most stringent bounds from unitarity and flavor physics., LaTeX, 11 pages, 5 figures

The associated production of neutral Higgs bosons with the Z gauge boson is investigated in the context of the future linear colliders, such as the ILC and CLIC, within the general two-Higgs-doublet model (2HDM). We compute the corresponding production cross-sections at one-loop, in full consistency with the available theoretical and phenomenological constraints. We find that the wave-function renormalization corrections to the external Higgs fields are the dominant source of the quantum effects, which turn out to be large and negative, and located predominantly in the region around \tan\beta=1 and moderate values of the parameter \lambda_5 (being \lambda_5 < 0). This behavior can be ultimately traced back to the enhancement potential of the triple Higgs boson self-couplings, a trademark feature of the 2HDM with no counterpart in the Higgs sector of the Minimal Supersymmetric Standard Model. The predicted Higgs-strahlung rates comfortably reach a few tens of femtobarn, which means barely 10^3 - 10^4 events per 500 inverse femtobarn of integrated luminosity. Due to their great complementarity, we argue that the combined analysis of the Higgs-strahlung events and the previously computed one-loop Higgs-pair production processes could be instrumental to probe the structure of the Higgs sector at future linac facilities., Comment: LaTeX, 16 pages, 9 Figures, 2 Tables. Extended discussion, references added, matches published version in Phys. Rev. D

The pairwise production of neutral Higgs bosons is analyzed in the context of the future linear colliders, such as the ILC and CLIC, within the general Two-Higgs-Doublet Model (2HDM). The corresponding cross-sections are computed at the one-loop level in full compliance with the current phenomenological bounds and the stringent theoretical constraints inherent to the consistency of the model. We uncover regions across the 2HDM parameter space, mainly for low tan\beta near 1 and moderate values of the relevant lambda_5 parameter, wherein the radiative corrections to the Higgs-pair production cross sections can comfortably reach 50% This behavior can be traced back to the enhancement capabilities of the trilinear Higgs self-interactions -- a trademark feature of the 2HDM, with no counterpart in the Minimal Supersymmetric Standard Model. Interestingly enough, the quantum effects are positive for energies around 500 GeV, thereby producing a significant enhancement in the expected number of events precisely around the fiducial startup energy of the ILC. The Higgs-pair production rates can be substantial, typically amounting to a few thousand events per 500 inverse femtobarn of integrated luminosity. In contrast, the corrections are negative in the highest energy range (1 TeV). We also compare the exclusive pairwise production of Higgs bosons with the inclusive gauge boson fusion channels leading to 2H+X finals states, and also with the exclusive triple Higgs boson production. We find that these multiparticle final states can be highly complementary in the overall Higgs bosons search strategy., Comment: 42 pages, 23 figures, 10 tables. Accepted in Phys. Rev. D (the published version is shorter)

The production of a single neutral Higgs boson h through (loop-induced) gamma-gamma collisions is explored in the context of the linear colliders within the general Two-Higgs-Doublet Model (2HDM). Two different mechanisms are analyzed: on the one hand, the scattering gamma gamma-> h of two real photons in a gamma-gamma collider; on the other, the more traditional mechanism of virtual photon fusion, e+e- -->e+e- + h. Owing to the peculiar properties of the Higgs boson self-interactions within the general 2HDM, we find that the overall production rates can be boosted up significantly, provided the charged Higgs mass is not too heavy. For example, if the latter is slightly above 100 GeV and, in addition, the lightest CP-even Higgs boson falls in the ballpark of the LEP bound on the SM Higgs mass up to a few hundred GeV, the cross-sections may typically render ��(gamma gamma-> h)= 0.1-1 pb and ��(e+e- --> e+e- + h)\sim 0.01 pb -- in both cases well above the SM prediction. Although for charged Higgs masses above 300 GeV the rates become virtually insensitive to the Higgs boson self-couplings, a significant tail of non-SM effects produced by the combined contribution of the Yukawa couplings and gauge bosons could still reveal a smoking gun., References and comments added. Accepted in Phys. Lett. B