Custodial Naturalness is a new symmetry-based idea to explain the large separation between the electroweak (EW) scale and ultraviolet completions of the Standard Model (SM). Classical scale invariance is combined with an enhanced scalar-sector custodial symmetry and both are spontaneously broken by dimensional transmutation at a new intermediate scale. The SM-like Higgs boson is an elementary pseudo-Nambu-Goldstone-Boson (pNGB) of the extended custodial symmetry, which naturally explains the suppression of the EW scale without a little hierarchy problem. We explain details of the general mechanism, its minimal realization and simplest extensions which populate Higgs-, gauge-, and neutrino portals and introduce candidates for particle Dark Matter (DM). We show the stability of the mechanism under inclusion of new sources of explicit custodial symmetry violation, as well as under variations of boundary conditions at the high scale. Custodial Naturalness is experimentally testable — including a specific correlation between the Higgs and top quark masses, as well as by the prediction of a new heavy $\textit{Z}$ gauge boson and a new dilaton-like scalar which are well-motivated targets for future colliders and Higgs factories. The cosmological evolution features a strongly supercooled phase transition implying that consequences of Custodial Naturalness may also be tested by gravitational wave observatories.

Germany

Thede Boer

Manfred Lindner

Portugal

Andreas Trautner

Custodial Naturalness

We give a fresh look at the WIMP paradigm by considering updated limits and prospects for direct and indirect dark matter detection and covering realistic dark matter models, beyond the so-called simplified models, which have been the target of experimental scrutiny. In particular, we investigate dark matter scenarios featuring dwindled direct detection signals, due to loop or momentum suppression. Therefore, this review extends previous reviews in different aspects and motivates the search for WIMP dark matter in light of the present and near-future detectors.

Italy

Giorgio Arcadi

Spain

David Cabo-Almeida

United States

Maíra Dutra

India

Pradipta Ghosh

France

Yann Mambrini

Brazil

Jacinto Neto

Mathias Pierre

Stefano Profumo

Chile

Farinaldo Queiroz

The waning of the WIMP: endgame?

Despite the remarkable success of the Standard Model, the hierarchy and patterns of fermion masses and mixings remain a profound mystery. To address this, we propose a model employing the rank mechanism, where the originally massless quarks and leptons sequentially get masses. The third generation masses originate from the seesaw mechanism at the tree-level, while those of the second and first generations emerge from one-loop and two-loop radiative corrections, respectively, with a progressive increase in the rank of the mass matrix. This approach does not require new discrete or global symmetries. Unlike other theories of this type that require the introduction of additional scalars, we employ the double seesaw mechanism within a left-right symmetric framework, which allows us to realize this scenario solely through gauge interactions.

Sudip Jana

Sophie Klett

Rabindra Mohapatra

Radiative origin of fermion mass hierarchy in left-right symmetric theory

We present “Custodial Naturalness” as a new mechanism to explain the separation between the electroweak (EW) scale and the scale of potential ultraviolet completions of the Standard Model (SM). We assume classical scale invariance as well as an extension of the SM scalar sector custodial symmetry to <math altimg='si1.svg'><mrow><mi mathvariant='normal'>SO</mi></mrow><mo stretchy='false'>(</mo><mn>6</mn><mo stretchy='false'>)</mo></math>. This requires a single new complex scalar field charged under a new <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mi mathvariant='normal'>X</mi></mrow></msub></math> gauge symmetry which partially overlaps with <math altimg='si3.svg'><mi>B</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></math>. Classical scale invariance and the high-scale scalar sector <math altimg='si1.svg'><mrow><mi mathvariant='normal'>SO</mi></mrow><mo stretchy='false'>(</mo><mn>6</mn><mo stretchy='false'>)</mo></math> custodial symmetry are radiatively broken by quantum effects that generate a new intermediate scale by dimensional transmutation. The little hierarchy problem is solved because the Higgs boson arises as an elementary (i.e. non-composite) pseudo-Nambu-Goldstone boson (pNGB) of the spontaneously broken <math altimg='si1.svg'><mrow><mi mathvariant='normal'>SO</mi></mrow><mo stretchy='false'>(</mo><mn>6</mn><mo stretchy='false'>)</mo></math> custodial symmetry. The minimal setting has the same number of parameters as the SM and predicts new physics in the form of a heavy <math altimg='si4.svg'><msup><mrow><mi>Z</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></math> with fixed couplings to the SM and a mass of <math altimg='si5.svg'><msub><mrow><mi>m</mi></mrow><mrow><msup><mrow><mi>Z</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></mrow></msub><mo>&#8776;</mo><mn>4</mn><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mn>100</mn><mspace width='0.2em' /><mrow><mi mathvariant='normal'>TeV</mi></mrow></math>, as well as a light but close-to invisible dilaton with a mass <math altimg='si6.svg'><msub><mrow><mi>m</mi></mrow><mrow><msub><mrow><mi>h</mi></mrow><mrow><mi mathvariant='normal'>&#934;</mi></mrow></msub></mrow></msub><mo>&#8776;</mo><mn>75</mn><mspace width='0.2em' /><mrow><mi mathvariant='normal'>GeV</mi></mrow></math>.

Thede de Boer

Electroweak hierarchy from conformal and custodial symmetry

We consider a model of boosted dark matter (DM), where a fraction of DM is upscattered to relativistic energies by cosmic ray electrons. Such interactions responsible for boosting the DM also attenuate its flux at the Earth. Considering a simple model of constant interaction cross section, we make analytical estimates of the variation of the attenuation ceiling with the DM mass and confirm it numerically. We then extend our analysis to a <math><msup><mi>Z</mi><mo>′</mo></msup></math>-mediated leptophilic DM model. We show that the attenuation ceiling remains nearly model independent for DM and mediator particles heavier than the electron, challenging some previous discussions on this topic. Using the XENONnT direct detection experiment, we illustrate how constraints based on energy-dependent scattering can significantly differ from those based on an assumed constant cross section. This highlights the importance of reevaluating these constraints in the context of specific models.

Tim Herbermann

Manibrata Sen

Attenuation of cosmic ray electron boosted dark matter

In this work, the sensitivity of future germanium-based reactor neutrino experiments to the weak mixing angle sin2 θ  W , and to the presence of new light vector bosons is investigated. By taking into account key experimental features with their uncertainties and the application of a data-driven and state-of-the-art reactor antineutrino spectrum, the impact of detection threshold and experimental exposure is assessed in detail for an experiment relying on germanium semiconductor detectors. With the established analysis framework, the precision on the Weinberg angle, and capability of probing the parameter space of a universally coupled mediator model, as well as a U(1)B−L-symmetric model are quantified. Our investigation finds the next-generation of germanium-based reactor neutrino experiments in good shape to determine the Weinberg angle sin2 θ  W  with &lt; 10% precision using the low-energetic neutrino channel of CEνNS. In addition, the current limits on new light vector bosons determined by reactor experiments can be lowered by about an order of magnitude via the combination of both CEνNS and EνeS. Consequently, our findings provide strong phenomenological support for future experimental endeavours close to a reactor site.

Thomas Rink

Light vector bosons and the weak mixing angle in the light of future germanium-based reactor CEνNS experiments

Little Higgs models address the hierarchy problem by identifying the SM Higgs doublet as pseudo-Nambu-Goldstone bosons arising from global symmetries with collective breakings. These models are designed to address the little hierarchy problem up to a scale of <math><mrow><mi>Λ</mi><mo>∼</mo><mi>O</mi><mo>(</mo><mn>10</mn><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>. Consequently, these models necessitate an UV completion above this scale. On the other hand, conformal extensions of the Standard Model are intriguing because scales emerge as a consequence of dimensional transmutation. In this study, we present a unified framework in which the electroweak hierarchy problem is tackled through a conformal symmetry collectively broken around the TeV scale, offering an appealing UV completion for little Higgs models. Notably, this framework automatically ensures the presence of the required UV fixed points, eliminating the need for careful adjustments to the particle content of the theory. Moreover, this framework naturally addresses the flavor puzzles associated with composite or little Higgs models. Furthermore, we suggest that in this framework all known little Higgs models can be UV completed through conformal dynamics above the scale <math><mi>Λ</mi></math> up to arbitrary high scales.

Aqeel Ahmed

Philipp Saake

Conformal little Higgs models

We infer the ultrahigh energy neutrino source by using the Glashow resonance candidate event recently identified by the IceCube Observatory. For the calculation of the cross section for the Glashow resonance, we incorporate both the atomic Doppler broadening effect and initial state radiation   <math> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>e</mi> </msub> <msup> <mi>e</mi> <mo>−</mo> </msup> <mo>→</mo> <msup> <mi>W</mi> <mo>−</mo> </msup> <mi>γ</mi> </math>  $$ {\overline{\nu}}_e{e}^{-}\to {W}^{-}\gamma $$ , which correct the original cross section considerably. Using available experimental information, we have set a generic constraint on the   <math> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>e</mi> </msub> </math>  $$ {\overline{\nu}}_e $$  fraction of astrophysical neutrinos, which excludes the μ-damped pγ source around 2σ confidence level under the assumption that neutrino production is dominated by the ∆-resonance. While a weak preference has been found for the pp source, next-generation measurements will be able to distinguish between ideal pp and pγ sources with a high significance assuming an optimistic single power-law neutrino spectrum. The inclusion of multi-pion production at very high energies for the neutrino source can weaken the discrimination power. In this case additional multimessenger information is needed to distinguish between pp and pγ sources.

Guo-yuan Huang

Nele Volmer

Inferring astrophysical neutrino sources from the Glashow resonance

The Standard Model (SM) of particle physics, being a local, unitary and Lorentz-invariant quantum field theory, remains symmetric under the combined action of Charge, Parity, and Time Reversal (CPT) symmetry. This automatically implies that fundamental properties of particles and antiparticles should be equal in magnitude. These fundamental tenets of the CPT principle have been put to stringent tests in recent Penning-trap experiments, where the matter-antimatter mass asymmetry has been measured. In light of these recent advances, we compare the bounds arising on CPT invariance from kaon systems with those from Penning-trap experiments. Using a simple yet powerful argument of mass decomposition of hadrons, we show that bounds on quark-antiquark mass differences from kaon oscillations are way beyond the reach of Penning-trap experiments. We lay out a roadmap to discuss possible reformulations of our understanding of the SM in the case of a discovery of CPT violation by these precision experiments.

Ting Cheng

Implications of a matter-antimatter mass asymmetry in Penning-trap experiments

The question of how heavy a sterile neutrino can be probed in experiments leads us to investigate the Primakoff production of heavy sterile neutrinos from ultrahigh-energy neutrinos via the magnetic dipole portal. Despite the suppression from the small magnetic moment, the transition is significantly enhanced by tiny t-channel momentum transfers, similar to the resonant production of pions and axions in an external electromagnetic field. Based on the current IceCube measurement of astrophysical neutrinos up to PeV energies, strong constraints can already be derived on the transition magnetic moments of sterile neutrinos up to TeV masses. Moreover, we investigate the sensitivity of future tau neutrino telescopes, which are designed for EeV cosmogenic neutrino detection. We find that sterile neutrino masses as large as <math><mn>30</mn><mspace width="0.25em"></mspace><mtext>TeV</mtext></math> can be probed at tau neutrino telescopes such as GRAND, POEMMA, and Trinity.

Werner Rodejohann

Probing heavy sterile neutrinos at neutrino telescopes via the dipole portal