arXiv subjects

Axel Maas

Publications and source records attributed to Axel Maas.

At least 19 recordsLinked to original sources

arXiv2026

Resonant scattering in two-flavored Sp(4) lattice gauge theories

We apply L\"uscher's method to the vector channel of the scattering amplitude of Pseudo-Nambu-Goldstone-Bosons (PNGBs), in the $Sp(4)$ lattice gauge theory coupled to $N_f=2$ flavors of Wilson-Dirac fundamental fermions. We generalize existing algorithms and numerical implementations of the method, to adapt them to this prominent candidate for the completion of proposed extensions of the Standard Model (SM). We present the first ab initio measurements of key properties of the vector resonances in the theory, including the coupling to the PNGBs, that are relevant to direct and indirect new physics searches, both for composite Higgs models (CHMs), as well as for strongly interacting massive particle (SIMP) realizations of dark matter. We also present a global update of the spectroscopy of the mesons in the theory, improving both the statistics and analysis systematics in respect to previous lattice measurements reported in the literature.

hep-lat↗

arXiv2026

Vector-channel scattering of dark particles in a Sp(4) gauge theory

We report new results obtained in our lattice studies of the $Sp(4)$ gauge theory coupled to two fundamental Dirac fermions. This theory provides a candidate for the dynamical origin of dark matter models within the strongly interacting massive particle paradigm. We employ L\"uscher's formalism to analyse finite-volume energy levels and study the scattering amplitude of two pseudoscalar states in the spin-1 channel. We present our preliminary findings for a set of ensembles generated within a broad range of (Wilson) fermion masses.

hep-lat↗

arXiv2026

Weak and Higgs physics from the lattice

The manifestly gauge-invariant and non-perturbatively complete lattice formulation of the weak interactions and the Brout-Englert-Higgs effect is connected to the usual perturbative description in phenomenology via the Fr\"ohlich-Morchio-Strocchi mechanism. However, slight differences between the two have been observed, which can potentially be accounted for by augmenting perturbation theory. We report on our ongoing lattice investigations of these additional effects using a setup with two generations of leptons coupled vectorially to the gauge-Higgs system. We explore the spectrum, inner structure in terms of weak (quasi-)PDFs, and spectral functions of the system to eventually compare cross sections to experimental results.

hep-lat↗

arXiv2025

Spectrum of the SU(2) scalar-fermion-gauge system under the influence of the Brout-Englert-Higgs effect

Gauge invariance requires physical states to be composite, even in the weak sector of the Standard Model (SM). The Fr\"ohlich-Morchio-Strocchi (FMS) mechanism resolves this subtlety and predicts additional Higgs contributions in SM processes. While this has been supported by theoretical investigations in the bosonic sector, its impact on fermionic observables remains largely unexplored. We use non-perturbative lattice techniques within a gauge-invariant framework to study a proxy theory of the weak sector with dynamical fermions. We determine the physical spectrum of the theory and interpret the results in the context of the FMS mechanism. Additionally, we identify suitable simulation points for a scattering analysis as a first step toward cross-sections relevant to (future lepton) colliders.

hep-lat↗

arXiv2025

Composite objects in quantum (super)gravity

It has been a long entertained idea that self-bound gravitons, so-called geons, could be a dark matter candidate or form (primordial) black holes. The development of viable candidates for quantum gravity allows now to investigate these ideas. Analytic methods show that the description of geons needs to be based on composite operators made out of the graviton field. We present results from a numerical investigation into this idea using causal dynamical triangulations, an ab-initio non-perturbative definition of quantum gravity based on general relativity, and accessible in lattice-gauge-theory-like simulations. Our results suggest an interesting dependence on cosmological time and other unexpected features. Finally, we extend the analytic part of the setting to a supergravity scenario. This provides hints which, if confirmed, could explain why supersymmetry may in a realistic universe in principle not be observable at low (collider) energy scales.

hep-lat↗

arXiv2025

Hints for a Geon from Causal Dynamic Triangulations

The existence of geons, physical states of self-bound gravitons, has long been proposed. In the context of four-dimensional causal dynamical triangulation simulations we investigate this possibility by measuring curvature-curvature correlators of different gravitational operators. We find a behavior consistent with a massive state, independent of the operators considered, over a certain distance window. While at most a hint, this is tantalizing due to its possible implications for dark matter or (primordial) black holes. We also find indications that the phase of rapid expansion of the obtained de Sitter universe impacts the mass, and relates to quantum fluctuations of space-time.

hep-lat↗

arXiv2025

Strongly Interacting Dark Matter admixed Neutron Stars

Dark matter may accumulate in neutron stars given its gravitational interaction and abundance. We investigate the influence of strongly-interacting dark matter, described by a QCD-like one-flavor $G_2$ gauge theory, on neutron stars. This choice allows to test, for the first time, a first-principles-determined non-Abelian dark matter equation of state, which supports composite fermionic dark matter and thus a Fermi-pressure-stabilized dark matter component. The ordinary matter part of the mixed star is described by available model-agnostic equations of state that interpolate between the low-density regime and high-density regime. We find that strongly-interacting dark matter has a similar impact on neutron stars as other model equation of states and confirm that strongly-interacting dark matter can be accommodated by constraints from neutron star observations within our uncertainties.

hep-ph↗

arXiv2025

The observable spectrum for GUT-like theories

The spectrum of nonabelian gauge theories cannot be described in terms of elementary particles, and so must be constructed from gauge-invariant composite operators, even in the presence of a Brout--Englert--Higgs effect. This leads to qualitative discrepancies in the prediction of the spectrum between perturbation theory and a full non-perturbative treatment in many theories. This is especially noticeable for GUTs. We present results corroborating this general statement using lattice simulations for a ''GUT-like'' toy theory, $\mathrm{SU}(3)$ Yang--Mills theory coupled to a Higgs field in the fundamental representation. Despite the apparent simplicity of the model, we find a rich spectrum with some previously unseen features. We also outline the next steps required to generate a large operator basis to extend this investigation to more realistic GUTs.

hep-lat↗

arXiv2025

Scattering of SIMPlectic Dark Pions

We study the scattering of two identical pNGBs (pseudo-Nambu-Goldstone Bosons) in Sp(4) gauge theory with two mass-degenerate Dirac fermions in the pseudo-real fundamental representation. This theory serves as a realization of a SIMP (Strongly Interacting Massive Particles) Dark Matter model. SIMPs are an exciting dark matter candidate as they make use of a new relic density mechanism and provide potential solutions to the so-called small-scale structure problems. These theories are realized by a confining dark sector which includes non-perturbative signatures. While most of the research focuses on ChPT (Chiral Perturbation Theory), first-principle verification of these models is indispensable. In these proceedings we give an update on scattering properties in the most common channel and give an outlook on the projects that lie ahead.

hep-lat↗

arXiv2024

Subleading Higgs effects at lepton colliders

Subtle field-theoretical effects suggest the presence of additional Higgs contributions in standard model processes. This has been supported by electroweak lattice calculation, e.\ g.\ for vector boson scattering. These effects can be included in perturbation theory by a suitable augmentation. We use such augmented perturbation theory to determine the impact at next-to-leading order at lepton colliders, from LEP to future machines such as FCC, in collisions with fermion-antifermion final states. After providing the formal background, we outline the calculational procedure, showing that in the fully exclusive process $e^-e^+\to f\bar{f}$ deviations only occur in fixed order at electroweak NNLO, but become relevant at the TeV scale already in resummed tree-level calculations. We discuss further processes where deviations are expected already at fixed-order NLO.

hep-ph↗

arXiv2024

Scattering of dark pions in Sp(4) gauge theory

Analyzes of astrophysical data provide first hints on the self-interactions of dark matter at low energies. Lattice calculations of dark matter theories can be used to investigate them, especially in the case of strongly-interacting dark matter. We consider Sp(4) gauge theory with two fundamental fermions as a candidate theory. We compute the scattering phase shift for the scattering of two identical dark pions and determine the parameters of the effective range expansion. Our exploratory results in the supposedly most common interaction channel provide a lower limit for the dark matter mass when compared to astrophysical data. We also provide first benchmarks of velocity-weighted cross-sections in the relevant non-relativistic domain.

hep-lat↗

arXiv2023

Scattering of dark pions in an Sp(4) gauge theory

In this work we consider strongly interacting dark matter candidates as composite states of $N_f=2$ fermions charged under a dark $Sp(4)$ gauge group in the fundamental representation. We give expressions that allow the calculation of correlation functions of two pseudo-Nambu-Goldstone-bosons with lattice field theory and present first results on the scattering phase shift in the isospin-2 channel in the theory from first principles. We give a lower limit on the dark matter particle mass by comparing our results with astrophysical constraints on the cross-section.

hep-lat↗

arXiv2023

The manifestly gauge-invariant spectrum of the Minimal Supersymmetric Standard Model

Formal field theory requires, even in the presence of a Brout-Englert-Higgs effect, to maintain manifest non-perturbative gauge invariance. The Fr\"ohlich-Morchio-Strocchi mechanism allows nonetheless an augmented perturbative treatment. We perform such an augmented tree-level analysis for the minimal supersymmetric standard model. We find that, as for the standard model, corrections to standard perturbation theory are only sub-leading.

hep-ph↗

arXiv2023

Experimental signatures of subtleties in the Brout-Englert-Higgs mechanism

Subtle, but long-known, field-theoretical aspects require a more refined treatment of gauge theories involving a Brout-Englert-Higgs effect. This refinement can be done analytically using the Fr\"ohlich-Morchio-Strocchi mechanism. In the standard model, this leads to slight, but in principle detectable, quantitative changes in observables. This can have significant implications for current and future colliders, which are investigated for a few sample processes.

hep-ph↗

arXiv2023

The Fr\"ohlich-Morchio-Strocchi mechanism: A underestimated legacy

There is an odd tension in electroweak physics. Perturbation theory is extremely successful. At the same time, fundamental field theory gives manifold reasons why this should not be the case. This tension is resolved by the Fr\"ohlich-Morchio-Strocchi mechanism. However, the legacy of this work goes far beyond the resolution of this tension, and may usher in a fundamentally and ontologically different perspective on elementary particles, and even quantum gravity.

hep-th↗

arXiv2023

Singlets in gauge theories with fundamental matter

We provide the first determination of the mass of the lightest flavor-singlet pseudoscalar and scalar bound states (mesons), in the $\rm{Sp}(4)$ Yang-Mills theory coupled to two flavors of fundamental fermions, using lattice methods. This theory has applications both to composite Higgs and strongly-interacting dark matter scenarios. We find the singlets to have masses comparable to those of the light flavored states, which might have important implications for phenomenological models. We focus on regions of parameter space corresponding to a moderately heavy mass regime for the fermions. We compare the spectra we computed to existing and new results for $\rm{SU}(2)$ and $\rm{SU}(3)$ theories, uncovering an intriguing degree of commonality. As a by-product, in order to perform the aforementioned measurements, we implemented and tested, in the context of symplectic lattice gauge theories, several strategies for the treatment of disconnected-diagram contributions to two-point correlation functions. These technical advances set the stage for future studies of the singlet sector in broader portions of parameter space of this and other lattice theories with a symplectic gauge group.

hep-lat↗

arXiv2022

Restoring the Bloch-Nordsieck theorem in the electroweak sector of the standard model

The electroweak gauge symmetry cannot be broken in a literal sense due to Elitzur's theorem. Thus, asymptotic states need to be manifestly and non-perturbatively gauge-invariant with respect to the electroweak symmetry. To take this suitably into account perturbation theory augmented by the Fr\"ohlich-Morchio-Strocchi mechanism can be used. We show that this restores the Bloch-Nordsieck theorem in electroweak processes in the standard model. This has potentially substantial impact at, e.g., future lepton colliders, but has only negligible effects at lower energies. We also demonstrate an alternative implementation using PDFs, which allows an approach with manifest electroweak Bloch-Nordsieck theorem also at hadron colliders.

hep-ph↗

arXiv2022

The spectrum of GUT-like gauge-scalar models

Past lattice simulations tentatively suggested that the spectrum of observable particles in BSM theories is qualitatively different than perturbatively expected. The discrepancy can be traced back to nontrivial field-theoretical effects arising from the requirement of gauge invariance. A perturbative but gauge-invariant approach working directly with bound states (as proposed by Fr\"ohlich, Morchio and Strocchi) could provide a solution, by allowing composite-state effects to be treated within a perturbative framework. We consider a toy GUT-like theory -- SU(3) Yang-Mills coupled to a scalar `Higgs' in the fundamental representation -- and expand on previous work by providing the most comprehensive spectroscopy to date, including all channels up to spin 2. Our results strongly support the general conclusion that the elementary spectrum is not an adequate proxy for the low-energy spectrum of a GUT, and also suggest a possible analytical approach to BSM model-building via the Fr\"ohlich-Morchio-Strocchi approach.

hep-lat↗