Search

The Next-to-Minimal 2-Higgs-Doublet Model (N2HDM) is an interesting benchmark model for a Higgs sector consisting of two complex doublet and one real singlet fields. Like the Next-to-Minimal Supersymmetric extension (NMSSM) it features light Higgs bosons that could have escaped discovery due to their singlet admixture. Thereby, the model allows for various different Higgs-to-Higgs decay modes. Contrary to the NMSSM, however, the model is not subject to supersymmetric relations restraining its allowed parameter space and its phenomenology. For the correct determination of the allowed parameter space, the correct interpretation of the LHC Higgs data and the possible distinction of beyond-the-Standard Model Higgs sectors higher order corrections to the Higgs boson observables are crucial. This requires not only their computation but also the development of a suitable renormalization scheme. In this paper we have worked out the renormalization of the complete N2HDM and provide a scheme for the gauge-independent renormalization of the mixing angles. We discuss the renormalization of the $\mathbb{Z}_2$ soft breaking parameter $m_{12}^2$ and the singlet vacuum expectation value $v_S$. Both enter the Higgs self-couplings relevant for Higgs-to-Higgs decays. We apply our renormalization scheme to different sample processes such as Higgs decays into $Z$ bosons and decays into a lighter Higgs pair. Our results show that the corrections may be sizeable and have to be taken into account for reliable predictions.

We discuss the current status of theoretical and experimental constraints on the real Higgs singlet extension of the Standard Model. For the second neutral (non-standard) Higgs boson the full mass range from 1 GeV to 1 TeV accessible at past and current collider experiments is considered. We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. We furthermore discuss electroweak corrections to the H to hh partial decay width within this model., Comment: 4 pages, 2 figures; Proceedings of 38th International Conference on High Energy Physics (ICHEP 2016) v2: Typo in affiliation corrected

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

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., Comment: no appendix

At the LHC, an effective theory of the Higgs sector allows us to analyze kinematic distributions in addition to inclusive rates, although there is no clear hierarchy of scales. We systematically analyze how well dimension-6 operators describe LHC observables in comparison to the full theory, and in a range where the LHC will be sensitive. The key question is how the breakdown of the dimension-6 description affects Higgs measurements during the upcoming LHC run for weakly interacting models. We cover modified Higgs sectors with a singlet and doublet extension, new top partners, and a vector triplet. First, weakly interacting models only generate small relevant subsets of dimension-6 operators. Second, the dimension-6 description tends to be justified at the LHC. Scanning over model parameters, significant discrepancies can nevertheless arise; their main source is the matching procedure in the absence of a well-defined hierarchy of scales. This purely theoretical problem should not affect future LHC analyses., Comment: 30 pages plus detailed appendices; v2: expanded discussion of matching procedure, new results added

If light--flavor squarks and gluinos are indeed heavy and chargino pair production is plagued with overwhelming backgrounds, pair production and associated production of stops and charginos will become the key signatures in the upcoming LHC runs. We present fully automated next-to-leading order predictions for heavy flavor squark production at the LHC, including stop-chargino associated production, based on MadGolem. We compute the total and differential NLO rates for a variety of MSSM scenarios with a light third generation. We focus on theoretical uncertainties on differential rates, including a comparison to multi-jet merging and the impact of bottom parton densities for stop-chargino associated production. We find that for the associated production channel the rates can reach tens of femtobarns, but the scale dependence does not provide a conservative estimate of the theoretical uncertainties., Comment: 17 Pages, 7 Figures, 3 tables

We study the production of Higgs boson pairs via gluon fusion at the LHC in the Two-Higgs-Doublet Model. We present predictions at NLO accuracy in QCD, matched to parton showers through the MC@NLO method. A dedicated reweighting technique is used to improve the NLO calculation upon the infinite top-mass limit. We perform our calculation within the MadGraph5_aMC@NLO framework, along with the 2HDM implementation based on the NLOCT package. The inclusion of the NLO corrections leads to large K-factors and significantly reduced theoretical uncertainties. We examine the seven 2HDM Higgs pair combinations using a number of representative 2HDM scenarios. We show how the model-specific features modify the Higgs pair total rates and distribution shapes, leading to trademark signatures of an extended Higgs sector., Comment: 39 pages, 10 figures, 11 tables, matching published version

We develop a technique to present Higgs coupling measurements, which decouple the poorly defined theoretical uncertainties associated to inclusive and exclusive cross section predictions. The technique simplifies the combination of multiple measurements and can be used in a more general setting. We illustrate the approach with toy LHC Higgs coupling measurements and a collection of new physics models., Comment: published version

Extended Higgs sectors appear in many models for physics beyond the Standard Model. Current Higgs measurements at the LHC are starting to significantly constrain them. We study their Higgs coupling patterns at tree level as well as including quantum corrections. Our benchmarks include a dark singlet-doublet extension and several two-doublet setups. Using SFitter we translate the current Higgs coupling measurements for one light Higgs state into their respective parameter spaces. Finally, we show how two-Higgs-doublet models can serve as a consistent ultraviolet completion of an assumed single Standard-Model-like Higgs boson with free couplings., Comment: 49 pages, including the updated SFitter Higgs couplings results for the Standard Model

We present search results based on next-to-leading order predictions for the pair production of color-adjoint leptons at the LHC. Quantum effects are sizable, dominated by pure QCD corrections, and sensitive to threshold effects. We illustrate the stabilization of scale dependences and confirm an excellent agreement between fixed-order and multi-jet predictions for representative distributions. Finally, we examine the trademark collider signatures of leptogluon pairs. Based on the CMS leptoquark search we derive a mass bound of 1.2-1.3 TeV for charged leptogluons, significantly improving the constraints available in the literature., Comment: LaTeX, 18 pages, 18 figures, 2 tables

After the recent discovery of a Higgs-like boson particle at the CERN LHC-collider, it becomes more necessary than ever to prepare ourselves for identifying its standard or non-standard nature. The Electroweak parameter Delta r relating the values of the gauge boson masses [MW,MZ] and the Fermi constant [G_F] is the traditional observable encoding high precision information of the electroweak physics at the quantum level. In this work we present a complete quantitative study of Delta r in the framework of the general (unconstrained) Two-Higgs-Doublet Model (2HDM). First of all we report on a systematic analysis of Delta r at the full one loop level in the general 2HDM, which to our knowledge was missing in the literature. Thereby we extract a theoretical prediction for the mass of the W-boson in this model, taking MZ, \alpha_{em} and G_F as experimental inputs. We find typical corrections leading to mass shifts $\delta MW \sim 20-40 MeV$ which help to improve the agreement with the experimentally measured value, in a degree no less significant than in the MSSM case. In the second part of our study we extend our calculation beyond the mere one-loop order. We devise an effective Lagrangian approach that captures the dominant higher order quantum effects on delta rho (viz. that part of Delta r describing the breaking of the approximate SU(2) custodial symmetry) in the limit of large Higgs boson self-interactions. This limit constitutes a telltale property of the general 2HDM which is unmatched by e.g. the MSSM. Our conclusion is that the Electroweak precision program to be conducted at the LHC, and maybe at a future linear collider, can nicely complement the direct searches. Should these distinctive loop effects be eventually found they would signal a smoking gun hinting at non-standard Higgs physics., Comment: LaTeX, 12 figures, 4 tables. Extended discussion, references added. Version accepted in Eur. Phys. J. C

We present completely general next-to-leading order predictions for squark and gluino production at the LHC, based on the fully automated MadGolem tool. Without any assumptions on the mass spectrum we predict production rates and examine the structure of the massless and massive quantum corrections. This allows us to quantify theory uncertainties induced by the spectrum assumptions commonly made. Going beyond total rates we compare general fixed-order distributions to resummed predictions from jet merging. As part of this comprehensive study we present the MadGolem treatment of ultraviolet, infrared and on-shell divergences., Comment: 28 pages, 20 figures, 4 tables

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., Comment: 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

Scalar color octets are generic signals for new physics at LHC energies. We examine their pair production at the LHC to next-to-leading order QCD. This computation serves as another test of the fully automized MadGolem framework. We find large NLO production rates and sizeable quantum effects which depend on the sgluon mass. The shift in the sgluon distributions is mild and in good agreement with a multi-jet merging calculation., Comment: 12 pages, 9 figures, 1 table

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., Comment: LaTeX, 11 pages, 5 figures

We revisit the production of a single Higgs boson from direct \gamma \gamma -scattering at a photon collider. We compute the total cross section \sigma(\gamma \gamma \to h) (for h=h0, H0, A0), and the strength of the effective g_{h \gamma \gamma} coupling normalized to the Standard Model (SM), for both the general Two-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric Standard Model (MSSM). In both cases the predicted production rates for the CP-even (odd) states render up to 10^4 (10^3) events per 500 \invfb of integrated luminosity, in full consistency with all the theoretical and phenomenological constraints. Depending on the channel the maximum rates can be larger or smaller than the SM expectations, but in most of the parameter space they should be well measurable. We analyze how these departures depend on the dynamics underlying each of the models, supersymmetric and non-supersymmetric, and highlight the possible distinctive phenomenological signatures. We demonstrate that this process could be extremely helpful to discern non-supersymmetric Higgs bosons from supersymmetric ones. Furthermore, in the MSSM case, we show that \gamma\gamma-physics could decisively help to overcome the serious impasse afflicting Higgs boson physics at the infamous "LHC wedge"., Comment: LaTeX, 16 pages, 6 Figures, 2 Tables. Minor typos fixed. Matches published version in Phys. Lett. B

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

We present a one-loop analysis of the pairwise production of neutral Higgs bosons (h0A0, H0A0) at linear colliders, such as the ILC and CLIC, within the general Two-Higgs-Doublet Model (2HDM). We single out sizable radiative corrections, which can well reach the level of 50 % and may be either positive (typically for \sqrt{s} \sim 0.5 TeV) and negative (for \sqrt{s} of 1 TeV and above). These large quantum effects, obtained in full agreement with the current phenomenological bounds and the stringent theoretical constraints on the parameter space of the model, can be traced back to the enhancement capabilities of the triple-Higgs self-interactions -- a trademark feature of the 2HDM, with no counterpart in e.g. the Minimal Supersymmetric Standard Model. In the most favorable scenarios, the Higgs-pair cross sections may be boosted up to barely 30 fb at the fiducial center-of-mass energy of 500 GeV -- amounting to a few thousand events per 500 inverse femtobarn of integrated luminosity. We also compare these results with several complementary double and triple Higgs-boson production mechanisms at order \alpha^3_{ew} and leading \alpha^4_{ew}, and we spotlight a plethora of potentially distinctive signatures of a Two-Higgs-Doublet structure of non-supersymmetric nature., Comment: 7 pages, 2 Figures, 2 Tables. To appear in the proceedings of the "9th International Symposium on Radiative Corrections (RADCOR 2009)", October 25-30 2009, Ascona, Switzerland

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 \sigma(gamma gamma-> h)= 0.1-1 pb and \sigma(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., Comment: References and comments added. Accepted in Phys. Lett. B

Inclusive Higgs boson pair production through the mechanism of gauge boson fusion e^{+} e^{-} -> V* V* -> h h + X (V=W,Z) in the general Two-Higgs-Doublet Model (2HDM), with h=h^0,H^0,A^0,H^{\pm}, is analyzed at order \alpha^4_{ew} in the linear colliders ILC and CLIC. This kind of processes is highly sensitive to the trilinear Higgs (3H) boson self-interactions and hence can be a true keystone in the reconstruction of the Higgs potential. For example, in the ILC at 1 TeV, the most favorable scenarios yield cross-sections up to roughly 1 pb, thus entailing 10^5 events per 100 fb^{-1} of integrated luminosity, whilst remaining fully consistent with the perturbativity and unitarity bounds on the 3H couplings, the electroweak precision data and the constraints from BR(b->s\gamma). Comparing with other competing mechanisms, we conclude that the Higgs boson-pair events could be the dominant signature for Higgs-boson production in the TeV-class linear colliders for a wide region of the 2HDM parameter space, with no counterpart in the Minimal Supersymmetric Standard Model. Owing to the extremely clean environment of these colliders, inclusive 2H events should allow a comfortable tagging and might therefore open privileged new vistas into the structure of the Higgs potential., Comment: LaTeX, 17 pages, 5 figures, 3 Tables. Extended discussion, Fig.4 corrected. Accepted in Phys. Lett. B

We analyze the production and subsequent decay of the neutral Higgs bosons of the MSSM into electrically neutral quark pairs qq'=bs,tc of different flavors at the LHC and compare with the direct FCNC production mechanisms. The cross-sections are computed in the unconstrained MSSM with minimal flavor-mixing sources and taking into account the stringent bounds from radiative B-meson decays. We extend the results previously found for these FCNC processes, which are singularly uncommon in the SM. Specifically, we report here on the SUSY-EW contribution of the Higgs-mediated FCNC cross-section into bs and tc final states and the SUSY-QCD and SUSY-EW contributions to bs-production. In this way, the complete map of MSSM predictions for the qq'-pairs produced at the LHC becomes available. The upshot is that the most favorable channels are: 1) the Higgs boson FCNC decays into bs, and 2) the direct production of tc pairs, both of them at the 1 pb level and mediated by SUSY-QCD effects. If, however, the latter are suppressed, we find a small SUSY-EW yield for the tc-production through Higgs decays but, at the same time, a cross-section of 0.1-1 pb for bs-production, which implies a significant number (10^4-10^5) of bs-pairs per 100 inverse femtobarn of integrated luminosity., Comment: LaTeX, 17 pages, 4 figures, 4 tables. Extended discussion. Accepted in Phys. Lett. B

We present a study of triple Higgs boson (3H) production at the International Linear Collider (ILC) within the general Two-Higgs-Doublet Model (2HDM). We compute the production cross-sections at the leading-order for the 3H final states and find values up to sigma ~ 0.1 pb. This result represents a large enhancement with respect to the corresponding MSSM cross-sections, which stay typically at the level of sigma ~ 10^(-6) pb or less. Furthermore, since the 3H cross-sections in the general 2HDM can be of the order of the double Higgs production cross-sections, such 3H processes could be a competitive (if not the dominant) mechanism for Higgs boson production at the ILC. In practice, these 3H events could be identified through the tagging of 6 heavy-quark jet final states and, in this case, they would provide strong evidence of an extended Higgs boson sector -- likely of non-supersymmetric nature., Comment: 5 pages, 1 figure. To appear in the proceedings of the "8th International Symposium on Radiative Corrections (RADCOR 2007)", October 1-5 2007, Florence, Italy

We discuss the production of single top-quark final states by direct supersymmetric flavor-changing interactions at the LHC. The total cross section pp(gg)->t\bar{c}+\bar{t}c is computed at the 1-loop order within the unconstrained MSSM. We prove that SUSY-QCD effects may furnish sizeable production rates amounting up to barely 10^5 t\bar{c}(c\bar{t}) events per 100 fb^{-1} of integrated luminosity, in full compliance with the stringent low-energy constraints from b->s gamma. Furthermore, we show that the cooperative SUSY-EW effects can be sizeable on their own, regardless of the SUSY-QCD contribution, with maximum production rates of the order of 10^3 events per 100 fb^{-1}. Owing to the fact that FCNC production of electrically neutral heavy-quark pairs is virtually absent within the SM, we conclude that the observation of such pp(gg)->t\bar{c}+\bar{t}c processes at the LHC could lead to evidence of new physics - of likely supersymmetric nature., Comment: LaTeX, 5 pages, 1 figure. To appear in the proceedings of the "8th International Symposium on Radiative Corrections (RADCOR 2007)", October 1-5 2007, Florence, Italy

(Abridged) We report on a complete study of the single top-quark production by direct supersymmetric flavor-changing neutral-current (FCNC) processes at the LHC. The total cross section for pp(gg)->t\bar{c}+\bar{t}c is computed at the 1-loop order within the unconstrained Minimal Supersymmetric Standard Model (MSSM). The present study extends the results of the supersymmetric strong effects (SUSY-QCD), which were advanced by some of us in a previous work, and includes the computation of the full supersymmetric electroweak corrections (SUSY-EW). Our analysis of pp(gg)->t\bar{c}+\bar{t}c in the MSSM has been performed in correspondence with the stringent low-energy constraints from b->s gamma. In the most favorable scenarios, the SUSY-QCD contribution can give rise to production rates of around 10^5 events per 100 fb^{-1} of integrated luminosity. Furthermore, we show that there exist regions of the MSSM parameter space where the SUSY-EW correction becomes sizeable. In the SUSY-EW favored regions, one obtains lower, but still appreciable, event production rates that can reach the 10^3 level for the same range of integrated luminosity. We study also the possible reduction in the maximum event rate obtained from the full MSSM contribution if we additionally include the constraints from B^0_s-\bar{B}^0_s. In view of the fact that the FCNC production of heavy quark pairs of different flavors is extremely suppressed in the SM, the detection of a significant number of these events could lead to evidence of new physics -- of likely supersymmetric origin., Comment: LaTex, 35 pages, typos corrected. Version accepted in JHEP

Triple Higgs boson production (3H) may provide essential information to reconstruct the Higgs potential. We consider 3H-production in the International Linear Collider (ILC) both in the Minimal Supersymmetric Standard Model (MSSM) and in the general Two-Higgs-doublet Model (2HDM). We compute the total cross-section for the various 3H final states, such as H^+ H^- h^0, H^0 A^0 h^0, etc. and compare with the more traditional double Higgs (2H) boson production processes. While the cross-sections for the 2H final states lie within the same order of magnitude in both the MSSM and 2HDM, we find that for the 3H states the maximum 2HDM cross-sections, being of order 0.1 pb, are much larger than the MSSM ones which in most cases are of order 10^{-6} pb or less. Actually, the 3H processes could be the dominant mechanism for Higgs boson production in the 2HDM. Ultimately the origin of the remarkable enhancement of the 3H channels in the 2HDM case (for both type I and type II models) originates in the structure of the trilinear Higgs boson couplings. The extremely clean environment of the ILC should allow a relatively comfortable tagging of the three Higgs boson events. In view of the fact that the MSSM contribution is negligible, these events should manifest themselves mainly in the form of 6 heavy-quark jet final states. Some of these signatures could be spectacular, and in case of being detected would constitute strong evidence of an extended Higgs sector of non-supersymmetric origin., Comment: LaTeX, 17 pages, 4 figures, 5 tables. References and comments added. Version accepted in Phys. Lett. B