We present a search for new scalar bosons predicted by the Inert Doublet Model at an $$e^+e^-$$ machine with centre-of-mass energies $$\sqrt{s} $$ of 240 and 365 $$\text {G}\text {eV}$$ . Within this model, four additional scalar bosons ( $$H,\, A,\, H^+$$ and $$H^-$$ ) are predicted. Due to an additional symmetry, the lightest new scalar, here chosen to be $\textit{H}$, is stable and provides an adequate dark matter candidate. The search for pair production of the new scalars is investigated in final states with two electrons or two muons, in the context of the future circular collider proposal, FCC-ee. Building on previous studies in the context of the CLIC proposal, this analysis extends the search to detector-level objects, using a parametric neural network to enhance the signal contributions over the Standard Model backgrounds, and sets projected exclusion and discovery contours in the $$M_A-M_H$$ vs. $$M_H$$ plane. With a total integrated luminosity of 10.8 (2.7) $$\,\hbox {ab}^{-1}$$ for $$\sqrt{s} =$$ 240 (365) $$\text {G}\text {eV}$$ , the discovery reach for the model goes up to $$M_H$$ $$= 108\,(157)\,\text {G}\text {eV}$$ for $$M_A-M_H$$ $$=15$$ $$\text {G}\text {eV}$$ at $$\sqrt{s} =$$ 240 (365) $$\text {G}\text {eV}$$ . For exclusion, almost the entire phase-space available in the $$M_A-M_H$$ vs. $$M_H$$ plane is expected to be ruled out at 95% CL, reaching up to $$M_H$$ $$=110\,(165)$$ $$\text {G}\text {eV}$$ .

United Kingdom

Anubha Bal

Edward Curtis

Anne-Marie Magnan

Benedikt Maier

Switzerland

Croatia

Tania Robens

Nicholas Wardle

Search for additional scalar bosons within the Inert Doublet Model in a final state with two leptons at the FCC-ee

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 $\textit{ℤ}$ 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 $$ {\mu}^{+}{\mu}^{-}\to {\nu}_{\mu }{\overline{\nu}}_{\mu } AA\to {\nu}_{\mu }{\overline{\nu}}_{\mu } jj\mathcal{ll} HH $$ , where $\textit{H}$ and $\textit{A}$ are the lightest and second-lightest new scalars and $\textit{ℓ}$ 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.

Germany

Johannes Braathen

Martin Gabelmann

Panagiotis Stylianou

Probing the Inert Doublet Model via vector-boson fusion at a muon collider

Interference effects are well founded from the quantum mechanical viewpoint and in principle cannot be ignored in realistic studies of New Physics scenarios. In this work, we investigate the size of interference effects between resonant and non-resonant contributions to di-Higgs production in the singlet extension of the Standard Model, where the additional heavy scalar provides a resonant channel. We find these interference contributions to have a non-negligible effect on the cross-sections and differential distributions. In order to allow for a computationally efficient treatment of these effects via reweighting, we introduce a new tool utilising a matrix-element reweighting method: HHReweighter. In addition to the broadly used di-Higgs invariant mass $\textit{m}$ , we analyse the sensitivity to the interference terms for other kinematic variables, such as the Higgs boson transverse momentum, and find that these also can be sensitive to interference effects. Furthermore, we provide updates on the latest experimental and theoretical limits on the parameter space of the real singlet extension of the Standard Model Higgs sector.

Finn Feuerstake

Elina Fuchs

Daniel Winterbottom

Interference effects in resonant di-Higgs production at the LHC in the Higgs singlet extension

We here report on the progress of the HHH Workshop, that took place in Dubrovnik in July 2023. After the discovery of a particle that complies with the properties of the Higgs boson of the Standard Model, all Standard Model (SM) parameters are in principle determined. However, in order to verify or falsify the model, the full form of the potential has to be determined. This includes the measurement of the triple and quartic scalar couplings.

Morocco

Hamza Abouabid

Abdesslam Arhrib

United States

Hannah Arnold

Duarte Azevedo

Vuko Brigljevic

Maggie Chen

Daniel Diaz

Javier Duarte

Netherlands

Tristan Pree

Jaouad Falaki

Dinko Ferencek

Portugal

Pedro. Ferreira

France

Benjamin Fuks

India

Japan

Sanmay Ganguly

Osama Karkout

Marina Kolosova

Jacobo Konigsberg

Greg Landsberg

Canada

China

Bingxuan Liu

CERN

Brian Moser

Margarete Mühlleitner

Andreas Papaefstathiou

Sweden

Roman Pasechnik

Rui Santos

Brian Sheldon

Gregory Soyez

Marko Stamenkovic

Tatjana Susa

Gilberto Tetlalmatzi-Xolocotzi

Georg Weiglein

Giulia Zanderighi

Rui Zhang

HHH whitepaper

Carlotta Accettura

Dean Adams

Rohit Agarwal

Claudia Ahdida

Italy

Chiara Aimè

Nicola Amapane

David Amorim

Paolo Andreetto

Fabio Anulli

Robert Appleby

Artur Apresyan

Aram Apyan

Sergey Arsenyev

Pouya Asadi

Egypt

Mohammed Mahmoud

Aleksandr Azatov

John Back

Lorenzo Balconi

Laura Bandiera

Roger Barlow

Nazar Bartosik

Emanuela Barzi

Fabian Batsch

Matteo Bauce

J. Berg

Andrea Bersani

Alessandro Bertarelli

Alessandro Bertolin

Kevin Black

Fulvio Boattini

Alex Bogacz

Maurizio Bonesini

Bernardo Bordini

Salvatore Bottaro

Luca Bottura

Alessandro Braghieri

Marco Breschi

Natalie Bruhwiler

Xavier Buffat

Laura Buonincontri

Philip Burrows

Graeme Burt

Dario Buttazzo

Barbara Caiffi

Marco Calviani

Simone Calzaferri

Daniele Calzolari

Rodolfo Capdevilla

Christian Carli

Fausto Casaburo

Massimo Casarsa

Luca Castelli

Maria Catanesi

Lorenzo Cavallucci

Gianluca Cavoto

Spain

Francesco Celiberto

Luigi Celona

Alessandro Cerri

Gianmario Cesarini

Cari Cesarotti

Grigorios Chachamis

Antoine Chance

Siyu Chen

Yang-Ting Chien

Mauro Chiesa

Anna Colaleo

Francesco Collamati

Gianmaria Collazuol

Marco Costa

Nathaniel Craig

Camilla Curatolo

David Curtin

Giacomo Molin

Magnus Dam

Heiko Damerau

Sridhara Dasu

Jorge Blas

Stefania Curtis

Ernesto Matteis

Stefania Rosa

Jean-Pierre Delahaye

Dmitri Denisov

Türkiye

Haluk Denizli

Christopher Densham

Radovan Dermisek

Luca Luzio

Elisa Meco

Biagio Micco

Keith Dienes

Eleonora Diociaiuti

Tommaso Dorigo

Alexey Dudarev

Robert Edgecock

Filippo Errico

Marco Fabbrichesi

Stefania Farinon

Anna Ferrari

Jose Somoza

Frank Filthaut

Davide Fiorina

Erratum: Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.

Towards a muon collider

We investigate the production of three Higgs bosons in the Two Real Singlet extension of the Standard Model, where the scalar sector is augmented by two additional real scalar fields which are singlets under the Standard Model gauge group. The model contains three neutral CP-even scalars, allowing for resonant production and asymmetric decay chains. We focus on the signature pp → h 3 → h 1 h 2 → h 1 h 1 h 1, where we identify h 3 as the heaviest scalar state, h 2 as the second heaviest and the lightest, h 1, as the Standard Model-like Higgs boson discovered by the Large Hadron Collider experiments. The dominant final state occurs when all three Higgs bosons decay to bottom-anti-bottom quark pairs, h 1 →   <math> <mi>b</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ b\overline{b} $$ , leading to 6 b-jets. Taking into account all current theoretical and experimental constraints, we determine the discovery prospects for this channel in future runs of the Large Hadron Collider, as well as in the high-luminosity phase.

Triple Higgs boson production at the Large Hadron Collider with Two Real Singlet scalars

We investigate the LHC phenomenology of a model where the Standard Model (SM) scalar sector is extended by two real scalar singlets. A $${{\mathbb {Z}}_2} \otimes {{\mathbb {Z}}_2} '$$ <math><mrow><msub><mi>Z</mi><mn>2</mn></msub><mo>⊗</mo><msup><mrow><msub><mi>Z</mi><mn>2</mn></msub></mrow><mo>′</mo></msup></mrow></math>  discrete symmetry is imposed to reduce the number of scalar potential parameters, which is spontaneously broken by the vacuum expectation values of the singlet fields. As a result, all three neutral scalar fields mix, leading to three neutral CP-even scalar bosons, out of which one is identified with the observed Higgs boson at 125 GeV. We explore all relevant collider signatures of the three scalars in this model. Besides the single production of a scalar boson decaying directly to SM particle final states, we extensively discuss the possibility of resonant multi-scalar production. The latter includes decays of the produced scalar boson to two identical scalars (“symmetric decays”), as well as to two different scalars (“asymmetric decays”). Furthermore, we discuss the possibility of successive decays to the lightest scalar states (“cascade decays”), which lead to experimentally spectacular three- and four-Higgs final states. We provide six benchmark scenarios for detailed experimental studies of these Higgs-to-Higgs decay signatures.

Tim Stefaniak

Jonas Wittbrodt

Two-real-scalar-singlet extension of the SM: LHC phenomenology and benchmark scenarios

We investigate the prospect of discovering the Inert Doublet Model scalars at CLIC. As signal processes, we consider the pair-production of inert scalars, namely e + e − → H + H − and e + e − → AH, followed by decays of charged scalars H ± and neutral scalars A into leptonic final states and missing transverse energy. We focus on signal signatures with two muons or an electron and a muon pair in the final state. A number of selected benchmark scenarios that cover the range of possible collider signatures of the IDM are considered. For the suppression of SM background with the same visible signature, multivariate analysis methods are employed. For several bench-mark points discovery is already possible at the low-energy stage of CLIC. Prospects of investigating scenarios that are only accessible at higher collider energies are also discussed.

Poland

Jan Kalinowski

Wojciech Kotlarski

Hungary

Brazil

Dorota Sokolowska

Aleksander Żarnecki

Exploring inert scalars at CLIC

In this work, we use a recast of the Run II search for invisible Higgs decays within Vector Boson Fusion to constrain the parameter space of the Inert Doublet model, a two Higgs doublet model with a dark matter candidate. When including all known theoretical as well as collider constraints, we find that the above can rule out a relatively large part in the $$m_H,\,\lambda _{345}$$ <math><mrow><msub><mi>m</mi><mi>H</mi></msub><mo>,</mo><mspace width="0.166667em"></mspace><msub><mi>λ</mi><mn>345</mn></msub></mrow></math>  parameter space, for dark scalar masses $$m_H\,\le \,100\,{\mathrm{GeV}}$$ <math><mrow><msub><mi>m</mi><mi>H</mi></msub><mspace width="0.166667em"></mspace><mo>≤</mo><mspace width="0.166667em"></mspace><mn>100</mn><mspace width="0.166667em"></mspace><mi>GeV</mi></mrow></math> . Including the latest dark matter constraints, a smaller part of parameter space remains which is solely excluded from the above analysis. We also discuss the sensitivity of monojet searches and multilepton final states from Run II.

Daniel Dercks

Constraining the Inert Doublet Model using Vector Boson Fusion