In recent years, the prospect of detecting gravitational waves sourced from a strongly first-order cosmological phase transition has emerged as one of the most exciting frontiers of gravitational wave astronomy. Cosmological phase transitions are an essential ingredient in the Standard Model of particle cosmology, and help explain the mechanism for creation of matter in the early Universe, provide insights into fundamental theories of physics, and shed light on the nature of dark matter. This underscores the significance of developing robust end-to-end tools for determining the resulting gravitational waves from these phase transitions. In this article we present , an improved version of the software package , designed for mapping cosmological phases and transitions in Standard Model extensions of multiple scalar fields. Building on the robust framework of its predecessor, extends its capabilities by including new features crucial for a more comprehensive analysis of cosmological phase transitions. It can calculate more complex properties, such as the bounce action through the path deformation method or an interface with , thermodynamic parameters, and gravitational wave spectra. Its applicability has also been broadened via incorporating the dimensionally reduced effective potential for models obtained from , as well as calculations in the $$\overline{\text {MS}}$$ and OS-like renormalisation schemes. This modular, flexible, and practical upgrade retains the speed and stability of the original , while significantly expanding its utility.

China

Peter Athron

Australia

Csaba Balázs

Andrew Fowlie

Lachlan Morris

William Searle

Yang Xiao

Yang Zhang

PhaseTracer2: from the effective potential to gravitational waves

We uncover two precise interpretations of traditional electroweak fine-tuning (FT) measures that were historically missed. (i) a statistical interpretation: the traditional FT measure shows the change in plausibility of a model in which a parameter was exchanged for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson mass relative to an untuned model in light of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson mass measurement. (ii) an information-theoretic interpretation: the traditional FT measure shows the exponential of the extra information, measured in nats, relative to an untuned model that you must supply about a parameter in order to fit the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> mass. We derive the mathematical results underlying these interpretations, and explain them using examples from weak scale supersymmetry. These new interpretations allow us to rigorously define FT in particle physics and beyond, shed fresh light on the status of extensions to the Standard Model and, lastly, allow us to precisely reinterpret historical and recent studies using traditional FT measures.

United States

Gonzalo Herrera

Precise interpretations of traditional fine-tuning measures

Several pulsar timing array collaborations recently reported evidence of a stochastic gravitational wave background (SGWB) at nHz frequencies. While the SGWB could originate from the merger of supermassive black holes, it could be a signature of new physics near the 100 MeV scale. Supercooled first-order phase transitions (FOPTs) that end at the 100 MeV scale are intriguing explanations, because they could connect the nHz signal to new physics at the electroweak scale or beyond. Here, however, we provide a clear demonstration that it is not simple to create a nHz signal from a supercooled phase transition, due to two crucial issues that could rule out many proposed supercooled explanations and should be checked. As an example, we use a model based on nonlinearly realized electroweak symmetry that has been cited as evidence for a supercooled explanation. First, we show that a FOPT cannot complete for the required transition temperature of around 100 MeV. Such supercooling implies a period of vacuum domination that hinders bubble percolation and transition completion. Second, we show that even if completion is not required or if this constraint is evaded, the Universe typically reheats to the scale of any physics driving the FOPT. The hierarchy between the transition and reheating temperature makes it challenging to compute the spectrum of the SGWB.

Chih-Ting Lu

Lei Wu

Yongcheng Wu

Zhongxiu Xu

Can Supercooled Phase Transitions Explain the Gravitational Wave Background Observed by Pulsar Timing Arrays?

The Bayes factor surface is a new way to present results from experimental searches for new physics. Searches are regularly expressed in terms of phenomenological parameters – such as the mass and cross-section of a weakly interacting massive particle. Bayes factor surfaces indicate the strength of evidence for or against models relative to the background only model in terms of the phenomenological parameters that they predict. They provide a clear and direct measure of evidence, may be easily reinterpreted, but do not depend on choices of prior or parameterization. We demonstrate the Bayes factor surface with examples from dark matter, cosmology, and collider physics.

The Bayes factor surface for searches for new physics

The BNL and FNAL measurements of the anomalous magnetic moment of the muon disagree with the Standard Model (SM) prediction by more than $$4\sigma $$ <math> <mrow> <mn>4</mn> <mi>σ</mi> </mrow> </math> . The hadronic vacuum polarization (HVP) contributions are the dominant source of uncertainty in the SM prediction. There are, however, tensions between different estimates of the HVP contributions, including data-driven estimates based on measurements of the R-ratio. To investigate that tension, we modeled the unknown R-ratio as a function of CM energy with a treed Gaussian process (TGP). This is a principled and general method grounded in data-science that allows complete uncertainty quantification and automatically balances over- and under-fitting to noisy data. Our tool yields exploratory results are similar to previous ones and we find no indication that the R-ratio was previously mismodeled. Whilst we advance some aspects of modeling the R-ratio and develop new tools for doing so, a competitive estimate of the HVP contributions requires domain-specific expertise and a carefully curated database of measurements (github, https://github.com/qiao688/TGP_for_g-2 ).

Qiao Li

Modeling the R-ratio and hadronic contributions to $$g-2$$ <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math> with a Treed Gaussian process

Using the GAMBIT global fitting framework, we constrain the MSSM with an eV-scale gravitino as the lightest supersymmetric particle, and the six electroweakinos (neutralinos and charginos) as the only other light new states. We combine 15 ATLAS and 12 CMS searches at 13 TeV, along with a large collection of ATLAS and CMS measurements of Standard Model signatures. This model, which we refer to as the $${{\tilde{G}}}$$ <math> <mover> <mi>G</mi> <mo>~</mo> </mover> </math> -EWMSSM, exhibits quite varied collider phenomenology due to its many permitted electroweakino production processes and decay modes. Characteristic $${{\tilde{G}}}$$ <math> <mover> <mi>G</mi> <mo>~</mo> </mover> </math> -EWMSSM signal events have two or more Standard Model bosons and missing energy due to the escaping gravitinos. While much of the $${{\tilde{G}}}$$ <math> <mover> <mi>G</mi> <mo>~</mo> </mover> </math> -EWMSSM parameter space is excluded, we find several viable parameter regions that predict phenomenologically rich scenarios with multiple neutralinos and charginos within the kinematic reach of the LHC during Run 3, or the High Luminosity LHC. In particular, we identify scenarios with Higgsino-dominated electroweakinos as light as 140 GeV that are consistent with our combined set of collider searches and measurements. The full set of $${{\tilde{G}}}$$ <math> <mover> <mi>G</mi> <mo>~</mo> </mover> </math> -EWMSSM parameter samples and GAMBIT input files generated for this work is available via Zenodo.

Norway

Viktor Ananyev

United Kingdom

Ankit Beniwal

Lasse Braseth

Andy Buckley

Jonathan Butterworth

Christopher Chang

Canada

Matthias Danninger

Germany

Tomás Gonzalo

Anders Kvellestad

CERN

France

Farvah Mahmoudi

Gregory Martinez

Markus Prim

Tomasz Procter

Are Raklev

Pat Scott

Patrick Stöcker

Jeriek Abeele

Martin White

Collider constraints on electroweakinos in the presence of a light gravitino

We investigate the extent to which perturbative calculations of the electroweak phase transition are arbitrary and uncertain, owing to their gauge, renormalisation scale and scheme dependence, as well as treatments of the Goldstone catastrophe and daisy diagrams. Using the complete parameter space of the Standard Model extended by a real scalar singlet with a ℤ2 symmetry as a test, we explore the properties of the electroweak phase transition in general R ξ and covariant gauges, OS and <math> <mover> <mi>MS</mi> <mo>¯</mo> </mover> </math> $$ \overline{\textrm{MS}} $$ renormalisation schemes, and for common treatments of the Goldstone catastrophe and daisy diagrams. Reassuringly, we find that different renormalisation schemes and different treatments of the Goldstone catastrophe and daisy diagrams typically lead to only modest changes in predictions for the critical temperature and strength of the phase transition. On the other hand, the gauge and renormalisation scale dependence may be significant, and often impact the existence of the phase transition altogether.

Japan

Graham White

How arbitrary are perturbative calculations of the electroweak phase transition?

In this work, we study the impact of electroweak and Higgs precision measurements at future electron-positron colliders on several typical supersymmetric models, including the constrained minimal supersymmetric Standard Model (CMSSM), nonuniversal Higgs mass generalizations (NUHM1, NUHM2), and the seven-dimensional minimal supersymmetric Standard Model (MSSM7). Using publicly available data from the <math><mrow><mi>GAMBIT</mi></mrow></math> community, we postprocess previous SUSY global fits with additional likelihoods to explore the discovery potential of Higgs factories, such as the Circular Electron Positron Collider (CEPC), the Future Circular Collider (FCC), and the International Linear Collider (ILC). We show that the currently allowed parameter space of these models will be further tested by future precision measurements. In particular, dark matter annihilation mechanisms may be distinguished by precise measurements of Higgs observables.

Csaba Balazs

Huifang Lv

South Korea

Wei Su

Jin Min Yang

Global fits of SUSY at future Higgs factories

A recent paper [1] accumulates evidence for a new fundamental particle by combining several CMS and ATLAS searches for the Standard Model Higgs boson. The putative particle is a neutral scalar, S, with a mass of about <math><mn>151</mn><mspace width="0.2em"></mspace><mtext>GeV</mtext></math>. The reported significances are 5.1σ local and 4.8σ global. This nearly reaches the 5σ threshold for a discovery in high-energy physics. In this brief note we cast doubt on the strength of the evidence for a new particle. After taking into account the fact that signals were fitted to six different channels, we find that the significances are only 4.1σ local and 3.5σ global. The code and instructions for reproducing our calculations are available at this github repo.

Comment on “Accumulating evidence for the associate production of a neutral scalar with mass around 151 GeV”

We assess the status of a wide class of WIMP dark matter (DM) models in light of the latest experimental results using the global fitting framework GAMBIT. We perform a global analysis of effective field theory (EFT) operators describing the interactions between a gauge-singlet Dirac fermion and the Standard Model quarks, the gluons and the photon. In this bottom-up approach, we simultaneously vary the coefficients of 14 such operators up to dimension 7, along with the DM mass, the scale of new physics and several nuisance parameters. Our likelihood functions include the latest data from Planck, direct and indirect detection experiments, and the LHC. For DM masses below 100 GeV, we find that it is impossible to satisfy all constraints simultaneously while maintaining EFT validity at LHC energies. For new physics scales around 1 TeV, our results are influenced by several small excesses in the LHC data and depend on the prescription that we adopt to ensure EFT validity. Furthermore, we find large regions of viable parameter space where the EFT is valid and the relic density can be reproduced, implying that WIMPs can still account for the DM of the universe while being consistent with the latest data.

Neal Kozar

Belgium

Sanjay Bloor

Torsten Bringmann

Joachim Brod

Jonathan Cornell

Ben Farmer

Will Handley

Felix Kahlhoefer

Sweden

Janina Renk

Italy

Andre Scaffidi

Aaron Vincent

Sebastian Wild

Jure Zupan

Thermal WIMPs and the scale of new physics: global fits of Dirac dark matter effective field theories