arXiv subjects

Johannes Braathen

Publications and source records attributed to Johannes Braathen.

At least 19 recordsLinked to original sources

arXiv2026

Impact of model-independent higher-order contributions to the Higgs-boson self-couplings

We point out the relevance of a new class of model-independent higher-order contributions to the trilinear and quartic self-couplings of the detected Higgs boson giving rise to potentially large effects of physics beyond the Standard Model (SM). It consists of SM-like diagrams with insertions of loop-corrected values for the trilinear and quartic Higgs self-couplings. While up to now predictions in specific models of physics beyond the SM were only evaluated up to the one-loop or, in some cases, up to the two-loop level, we demonstrate how potentially large higher-order contributions can consistently be incorporated into existing one-loop or two-loop predictions. These model-independent higher-order contributions therefore improve the existing predictions that were obtained in specific models. Confronting our predictions with the relevant experimental results and theoretical constraints, we perform a simultaneous determination of the trilinear and quartic Higgs-boson self-couplings. We show that the new set of model-independent higher-order contributions can induce sizeable shifts in the inferred bounds on the trilinear and quartic Higgs self-couplings. For example, including the new higher-order corrections can shift the upper bound on the trilinear self-coupling modifier entering the theoretical predictions to $\sim4.9$ from the experimental limit of $ 6.1$. Our results demonstrate that incorporating these higher-order contributions is essential for a reliable interpretation of present and future measurements. We further provide a public tool that implements these effects and enables direct comparison with experimental limits.

hep-ph↗

arXiv2026

Complementarity of gravitational wave analyses and di-Higgs production in the exploration of the Electroweak Phase Transition dynamics in the RxSM

The real singlet extension of the Standard Model (SM), RxSM, is one of the simplest Beyond-the-Standard Model (BSM) theories that can accommodate a strong first-order electroweak phase transition (SFOEWPT). We survey the possible thermal histories of the early Universe in the RxSM, and find that a SFOEWPT can occur in this model as single- or two-step phase transitions. We investigate complementary approaches to probe such scenarios experimentally: either via searches for a stochastic background of gravitational waves (GWs) or via searches for di-Higgs production processes at future collider experiments: the HL-LHC, or a possible high-energy $e^+e^-$ collider. For these analyses we consistently include one-loop corrections to the trilinear Higgs couplings. We find that entirely different phenomenological signals are possible, depending on how the SFOEWPT occurs. In scenarios where such a transition is driven by the Higgs doublet direction in field space, BSM deviations in properties of the detected Higgs boson, particularly in the trilinear scalar coupling, typically lead to observable signals at colliders, while the regions of parameter space with detectable GW signals are very narrow. On the other hand, if the SFOEWPT is triggered by the singlet field direction, the detected Higgs boson is very SM-like and no signs of BSM physics would appear in di-Higgs production processes. However, strong GW signals could be produced for significant parts of the RxSM parameter space with singlet-driven SFOEWPT. This work highlights the crucial importance of exploiting complementary experimental directions to determine the dynamics of the electroweak phase transition and access the shape of the Higgs potential realised in Nature.

hep-ph↗

arXiv2026

Investigating a strong first-order electroweak phase transition in the RxSM at future linear $e^+e^-$ colliders and LISA

The general real singlet extension of the Standard Model (SM), the RxSM, is one of the simplest theories Beyond-the-Standard Model (BSM) that can accommodate a strong first-order electroweak phase transition (SFOEWPT). We investigate the possible thermal histories of the scalar potential in the RxSM, and the regions of the model parameter space in which SFOEWPT can be realised. We then explore complementary avenues to probe such scenarios experimentally: either using searches for a stochastic background of gravitational waves (GWs), or using searches for di-Higgs production processes at future collider experiments, focusing on the case of a high-energy $e^+e^-$ collider. An important aspect of our work is that one-loop corrections to all relevant trilinear scalar couplings are consistently included both in the calculation of dynamics of the electroweak phase transition (EWPT) and in collider processes. We find entirely different phenomenological signatures for different parts of the RxSM parameter space giving rise to SFOEWPTs. On the one hand, if the SFOEWPT is driven by the singlet field, the 125 GeV Higgs boson is very SM-like and signs of BSM physics would be difficult to find at colliders, but strong GW signals could be produced. On the other hand, in scenarios where a SFOEWPT is driven by the doublet field, BSM deviations in properties of the detected Higgs boson, particularly in its trilinear self-coupling, typically lead to observable signals at colliders, while detectable GW signals are much more challenging to achieve. This work highlights the complementarity of collider experiments and cosmological observations to determine the dynamics of the EWPT and reconstruct the shape of the Higgs potential realised in Nature.

hep-ph↗

arXiv2026

Refining two-loop corrections to trilinear Higgs couplings in the Two-Higgs-Doublet Model

The precise determination of the Higgs self-couplings is an essential task for understanding electroweak symmetry breaking and probing physics beyond the Standard Model (SM). The calculation of two-loop corrections to scalar couplings is important as it provides a critical test of the perturbative stability of the theoretical predictions, especially in scenarios with extended scalar sectors where large one-loop corrections can occur. Moreover, two-loop corrections need to be taken into account for the future perspective of precisely measuring the trilinear Higgs self-coupling. We present new results for the leading two-loop corrections to trilinear Higgs couplings in the Two-Higgs-Doublet Model (2HDM). We focus in particular on the couplings $λ_{hhh}$ and $λ_{hhH}$, which are relevant for Higgs pair production at the (HL-)LHC or at future linear colliders. We address the renormalisation of the alignment limit in the Higgs basis and give some insights into technical details of the calculation. Finally, we discuss the phenomenological impact of our results on di-Higgs production differential distributions.

hep-ph↗

arXiv2026

Precision predictions for trilinear scalar couplings and Higgs pair production in models with extended scalar sectors

Reconstructing the shape of the Higgs potential realised in Nature is one of the most pressing tasks of current and future colliders. This will offer deep insights into the dynamics of the electroweak phase transition and provide a unique opportunity to probe physics beyond the Standard Model (BSM). In this context, it is essential to have precise theory predictions for trilinear scalar couplings, which control the form of the potential, and for Higgs pair production processes, which are the observables that allow accessing the trilinear couplings. I summarise in these proceedings recent progress in precision calculations of both trilinear scalar couplings and Higgs pair production at the (HL-)LHC in BSM models with extended scalar sectors.

hep-ph↗

arXiv2026

Precise predictions for trilinear Higgs couplings and Higgs pair production in extended scalar sectors with anyH3 and anyHH

A central objective of future collider experiments is to probe the structure of the Higgs potential, which requires access to trilinear scalar couplings, in particular the self-coupling of the observed Higgs boson. While this coupling is fixed in the Standard Model (SM), it can receive sizable modifications in many Beyond the SM (BSM) scenarios, often connected to solutions of open problems such as the origin of the matter-antimatter asymmetry of the Universe. In theories with extended scalar sectors, radiative corrections involving additional scalar states can significantly affect both the Higgs self-coupling and other trilinear scalar interactions, with important consequences for predictions of physical observables. Precise theoretical calculations are therefore essential for the interpretation of precision Higgs measurements and for identifying indirect signatures of new physics. This contribution presents the latest version of the public tool anyBSM, which provides automated calculations of all trilinear scalar couplings at full one-loop order in arbitrary renormalisable theories, including full momentum dependence and flexible renormalisation-scheme choices. In addition, the new module anyHH for di-Higgs production in gluon fusion is discussed in several exemplary BSM models, including scenarios with multiple resonances.

hep-ph↗

arXiv2026

Sensitivity to new physics: single-Higgs couplings vs. the trilinear Higgs coupling

The trilinear Higgs self-coupling provides a unique probe of the structure of the Higgs potential and of the nature of the electroweak phase transition, and constitutes a key target for future collider experiments. Recent studies have shown that confronting theoretical predictions for the trilinear Higgs coupling with current experimental bounds offers a powerful and complementary way to test effects of physics beyond the Standard Model (BSM), in particular those arising from extended Higgs sectors. Meanwhile, substantial progress has been achieved in the precise calculation and automation of the trilinear Higgs coupling in a wide class of BSM models. This contribution discusses several BSM scenarios, compatible with existing constraints, in which sizeable deviations in the trilinear Higgs coupling w.r.t. the Standard Model (SM) value are predicted, while other Higgs observables remain close to their SM expectations and are therefore difficult to probe experimentally. These results highlight the strong physics motivation for a precise measurement of the trilinear Higgs coupling at a future Higgs factory.

hep-ph↗

arXiv2025

Assessing uncertainties in the determination of the trilinear Higgs self-coupling from single-Higgs observables

Circular $e^{+}e^{-}$ colliders operating at energies below the di-Higgs production threshold can provide information on the trilinear Higgs self-coupling $λ_{hhh}$ via its loop contributions to single Higgs production processes and electroweak precision observables. We investigate how well a non-SM value of $λ_{hhh}$ can be determined indirectly via its loop contributions within a global EFT fit. Using an inert doublet extension of the SM Higgs sector as an example for a scenario of physics beyond the SM that could be realised in nature, we find that theoretical uncertainties related to the treatment of loop contributions and the truncation of the EFT expansion, which are usually neglected, play an important role in determining the sensitivity to $λ_{hhh}$ in a global fit. The results obtained from such an indirect determination of $λ_{hhh}$ without taking these additional uncertainties into account would be too optimistic, leading to an artificially high resulting precision for $λ_{hhh}$. They could therefore be misleading in the quest to precisely identify the underlying physics of electroweak symmetry breaking.

hep-ph↗

arXiv2025

MuCol Milestone Report No. 7: Consolidated Parameters

This document is comprised of a collection of consolidated parameters for the key parts of the muon collider. These consolidated parameters follow on from the October 2024 Preliminary Parameters Report. Attention has been given to a high-level consistent set of baseline parameters throughout all systems of the complex, following a 10 TeV center-of-mass design. Additional details of the designs contributing to this baseline design are featured in the appendix. Likewise, explorative variations from this baseline set can be found in the appendix. The data is collected from a collaborative spreadsheet and transferred to overleaf.

physics.acc-ph↗

arXiv2025

Impact of one-loop corrections to trilinear scalar couplings on di-Higgs production in the RxSM

We investigate di-Higgs production at the (HL-)LHC and possible high-energy future $e^+e^-$ colliders within the real Higgs singlet extension of the Standard Model (SM), the RxSM. This model has two CP-even Higgs bosons, $h$ and $H$, for which we assume $m_h\sim 125 \text{ GeV} < m_H$. We analyse the effect of one-loop corrections to the two trilinear scalar couplings relevant for di-Higgs production, $λ_{hhh}$ and $λ_{hhH}$, by performing an extensive parameter scan within the RxSM. We find that the one-loop corrections have a strong impact on the total production cross-sections, as well as on the differential cross-sections with respect to the invariant di-Higgs mass, $m_{hh}$. We evaluate the sensitivity of the HL-LHC and a high-energy $e^+e^-$ collider with $\sqrt{s} = 1 \text{ TeV}$, the ILC1000, to probe BSM physics effects in these processes. We demonstrate that the RxSM can be distinguished from the SM for large parts of the sampled parameter space. The resonant $H$ structure in the $m_{hh}$ distribution, on the other hand, can be observed only if the corresponding couplings, in particular $λ_{hhH}$, are sufficiently large. Here the ILC1000 yields a substantially better sensitivity than the HL-LHC.

hep-ph↗

arXiv2025

Probing the Higgs potential at a Photon Collider

A $γγ$ collider, either in conjunction with an $e^+e^-$ linear collider or as a stand-alone facility, offers a very attractive Higgs physics programme at relatively low centre-of-mass (c.m.) energies. While the Higgs boson that has been discovered at the LHC can be studied in detail in resonant production at 125~GeV, a c.m.\ energy as low as 280~GeV can probe the Higgs potential via the Higgs pair production process providing access to the trilinear Higgs-boson self-coupling. High polarisation of the photon beams (produced via Compton back-scattering) can be achieved and adjusted by flipping the polarisation of the incident laser. The prospects for exploring the Higgs pair production process at a $γγ$ collider are assessed by comparing different running scenarios utilising different types of the incident laser. The possibility to use photon polarisations for disentangling different kinds of contributions to the Higgs pair production process is emphasised.

hep-ph↗

arXiv2025

Generic two-loop results for trilinear and quartic scalar self-interactions

Reconstructing the shape of the Higgs potential realised in Nature is a central part of the physics programme at the LHC and future colliders. In this context, accurate theoretical predictions for trilinear and quartic Higgs couplings are becoming increasingly important. In this paper, we present results that enable significant progress in the automation of these calculations at the two-loop level in a wide range of models. Specifically, we calculate the generic two-loop corrections for scalar n-point functions with n<=4 assuming that all external scalars are identical. Working in the zero-momentum approximation, we express the results in terms of generic couplings and masses. Additionally, by exploiting permutation invariances, we reduce the number of Feynman diagrams appearing to a substantially smaller set of basis diagrams. To ease the application of our setup, we also provide routines that allow to map our generic results to scalar two-loop amplitudes generated with the package FeynArts. We perform a series of calculations to cross-check our results with existing results in the literature. Moreover, we present new two-loop results for the trilinear Higgs coupling in the general singlet extension of the Standard Model. We also present the public Python package Tintegrals, which allows for fast and stable evaluations of all relevant two-loop integrals with vanishing external momenta.

hep-ph↗

arXiv2025

Probing the Inert Doublet Model via Vector-Boson Fusion at a Muon Collider

In this work, we explore the discovery potential of the Inert Doublet Model (IDM) via the vector boson fusion (VBF) channel at a muon collider with centre-of-mass energy of 10 TeV. The Inert Doublet Model is a two-Higgs-doublet model variant with an unbroken discrete $\mathbb{Z}_2$ symmetry, featuring new stable scalar particles that can serve as dark matter candidates. Current dark matter data constrain the phenomenologically viable parameter space of the IDM and render certain collider signatures elusive due to tiny couplings. However, VBF-type processes can still exhibit significant enhancements compared to the Standard Model, presenting a promising avenue to probe the IDM at a high-energy muon collider. We consider as our specific target process $μ^+μ^-\to ν_μ\barν_μAA\to ν_μ\barν_μjj \ell\ell HH$, where $H$ and $A$ are the lightest and second-lightest new scalars and $\ell$ can be electrons or muons. We perform both cut-based and machine-learning improved sensitivity analyses for such a signal, finding a population of promising benchmark scenarios. We additionally investigate the impact of the collider energy by comparing sensitivities to the target process at 3 TeV and 10 TeV. Our results provide a clear motivation for a muon collider design capable of reaching a 10 TeV centre-of-mass energy. We furthermore discuss constraints stemming from new-physics corrections to the Higgs to di-photon decay rate as well as the trilinear Higgs coupling in detail, using state-of-the-art higher-order calculations.

hep-ph↗

arXiv2025

Leading two-loop corrections to the Higgs di-photon decay in the Inert Doublet Model

Leading two-loop contributions to the di-photon decay of the Higgs boson are evaluated for the first time in the Inert Doublet Model (IDM). We employ for this calculation the Higgs low-energy theorem, meaning that we obtain corrections to the Higgs decay process by taking Higgs-field derivatives of the leading two-loop contributions to the photon self-energy. Specifically, we have included corrections involving inert BSM Higgs bosons and gauge bosons, as well as external-leg contributions involving inert scalars, gauge bosons and fermions. Our calculation has been performed with a full on-shell renormalization, and in the gauge-less limit. Moreover, we performed two independent calculations, using the background-field method and the pinch technique, in order to apply the Higgs low-energy theorem consistently, and found full agreement between the two calculations. We investigate our results numerically in two scenarios of the IDM: one with a light dark matter (DM) candidate (Higgs resonance scenario), and another with all additional scalars heavy (heavy Higgs scenario). In both cases, we find that the inclusion of two-loop corrections qualitatively modifies the behavior of the decay width, compared with the one-loop ($i.e.$ leading) order, and that they increase the deviation from the Standard Model. Furthermore, we demonstrate that the inclusion of the newly-computed two-loop corrections is essential to reliably interpret the observation or non-observation of a deviation in the Higgs di-photon decay width at current and future colliders.

hep-ph↗

arXiv2025

The Muon Collider

Muons offer a unique opportunity to build a compact high-energy electroweak collider at the 10 TeV scale. A Muon Collider enables direct access to the underlying simplicity of the Standard Model and unparalleled reach beyond it. It will be a paradigm-shifting tool for particle physics representing the first collider to combine the high-energy reach of a proton collider and the high precision of an electron-positron collider, yielding a physics potential significantly greater than the sum of its individual parts. A high-energy muon collider is the natural next step in the exploration of fundamental physics after the HL-LHC and a natural complement to a future low-energy Higgs factory. Such a facility would significantly broaden the scope of particle colliders, engaging the many frontiers of the high energy community. The last European Strategy for Particle Physics Update and later the Particle Physics Project Prioritisation Panel in the US requested a study of the muon collider, which is being carried on by the International Muon Collider Collaboration. In this comprehensive document we present the physics case, the state of the work on accelerator design and technology, and propose an R\&D project that can make the muon collider a reality.

physics.acc-ph↗

arXiv2024

anyH3: precise predictions for the trilinear Higgs coupling in the Standard Model and beyond

The trilinear Higgs coupling $λ_{hhh}$ of the detected Higgs boson is an important probe for physics beyond the Standard Model. Correspondingly, improving the precision of the theoretical predictions for this coupling as well as the experimental constraints on it are among the main goals of particle physics in the near future. In this article, we present the public $\mathtt{Python}$ code $\mathtt{anyH3}$, which provides precise theoretical predictions for $λ_{hhh}$. The program can easily be used for any renormalisable model, where for the input the $\mathtt{UFO}$ format is adopted. It allows including corrections up to the full one-loop level with arbitrary values of the external squared momenta and features a semi-automatic and highly flexible renormalisation procedure. The code is validated against known results in the literature. Moreover, we present new results for $λ_{hhh}$ in models which so far have not been investigated in the literature.

hep-ph↗

arXiv2023

Precise predictions for the trilinear Higgs self-coupling in the Standard Model and beyond

Deviations in the trilinear self-coupling of the Higgs boson at 125 GeV from the Standard Model (SM) prediction are a sensitive test of physics Beyond the SM (BSM). The LHC experiments searching for the simultaneous production of two Higgs bosons start to become sensitive to such deviations. Therefore, precise predictions for the trilinear Higgs self-coupling in different BSM models are required in order to be able to test them against current and future bounds. We present the new framework $\texttt{anyH3}$, which is a $\texttt{Python}$ library that can be utilized to obtain predictions for trilinear scalar couplings up to the one-loop level in any renormalisable theory. The program makes use of the $\texttt{UFO}$ format as input and is able to automatically apply a wide variety of renormalisation schemes involving minimal and non-minimal subtraction conditions. External-leg corrections are also computed automatically, and finite external momenta can be optionally taken into account. The $\texttt{Python}$ library comes with convenient command-line as well as $\texttt{Mathematica}$ user interfaces. We perform cross-checks using consistency conditions such as UV-finiteness and decoupling, and also by comparing against results know in the literature. As example applications, we obtain results for the trilinear self-coupling of the SM-like Higgs boson in various concrete BSM models, study the effect of external momenta as well as of different renormalisation schemes.

hep-ph↗

arXiv2023

Experimental probes and theoretical concepts for BSM trilinear couplings: a case study for scalar top quarks

After the possible discovery of new particles, it will be crucial to determine the properties, and in particular the couplings, of the new states. Here, we focus on scalar trilinear couplings, employing as an example the case of the trilinear coupling of scalar top quarks (stops) to the Higgs boson in the Minimal Supersymmetric Standard Model (MSSM). We discuss possible strategies for experimentally determining the stop trilinear coupling parameter, which controls the stop--stop--Higgs interaction, and we demonstrate the impact of different prescriptions for the renormalisation of this parameter. We find that the best prospects for determining the stop trilinear coupling arise from its quantum effects entering the model prediction for the mass of the SM-like Higgs boson in comparison to the measured value, pointing out that the prediction for the Higgs-boson mass has a high sensitivity to the stop trilinear coupling even for heavy masses of the non-standard particles. Regarding the renormalisation of the stop trilinear coupling, we identify a renormalisation scheme that is preferred given the present level of accuracy, and we clarify the origin of potentially large logarithms that cannot be resummed with standard renormalisation group methods.

hep-ph↗