Extended Scalar Sectors From All Angles

21 Oct 2024, 09:00 → 25 Oct 2024, 18:45 Europe/Zurich

503/1-001 - Council Chamber (CERN)

Emanuele Angelo Bagnaschi (INFN Laboratori Nazionali di Frascati), Maria Cepeda (CIEMAT), Joe Davighi, Ian Lewis (The University of Kansas), Tania Robens (Rudjer Boskovic Institute (HR)), Nikolaos Rompotis (University of Liverpool (UK))

In this workshop, we plan to investigate new physics models from a large variety of viewpoints and perspectives.

After the discovery of a scalar boson that currently complies with the predictions for the Higgs boson of the Standard Model (SM), particle physics has entered an exciting era.

To date, the LHC experiments have confirmed predicted properties of such a boson, in particular the mass as well as couplings to other SM final states, to great precision. However, both theoretical and experimental accuracy still leave room for new physics models.

We here plan to focus on models with extended scalar sectors. Depending on the specific model, such scenarios can help to address additional questions that cannot be answered by the SM alone.

This concise workshop will bring together theorists and experimentalists to discuss current status and future perspectives for the discovery of such new physics scenarios.

 

 

Monday 21 October

09:00 → 09:15 Welcome

Conveners: Emanuele Angelo Bagnaschi (INFN Laboratori Nazionali di Frascati), Tania Natalie Robens (Rudjer Boskovic Institute (HR))

welcome.pdf

09:15 → 10:45 Invited Plenaries

Convener: Tao Han

09:15 Extended Scalars Overview

Speaker: Rui Santos (ISEL and CFTC-UL)

ESFAA_2024_Santos.key

ESFAA_2024_Santos.pdf

10:00 Overview of BSM Higgs searches at the LHC

Speaker: Halil Saka (University of Cyprus (CY))

BSMHiggs-2024-HalilSaka.pdf

10:45 → 11:15 Coffee Break

11:15 → 12:35 Contributed Talks

Convener: Marcin Badziak

11:15 Higgs Sector in B-L Supersymmetric Standard Model

We explore the TeV-scale $B-L$ extension of the Minimal Supersymmetric Standard Model (BLSSM), which incorporates a seesaw mechanism for generating light neutrino masses. This presentation focuses on the phenomenological implications of the Higgs sector within this model, highlighting unique features and potential experimental signatures that could be investigated in current and future collider experiments.

Speaker: Prof. Shaaban Khalil (Zewail City of Science and Technology)

BLSSM_Higgs_CERN.pdf

11:35 Electroweak hierarchy from conformal and custodial symmetry

I will introduce the idea of "Custodial Naturalness" to explain the origin of the electroweak hierarchy. Custodial Naturalness is based on classical scale invariance as well as an extension of the Standard Model (SM) scalar sector custodial symmetry to SO(6). This requires a single new complex scalar field charged under a new U(1)​ gauge symmetry which partially overlaps with B−L. Classical scale invariance and the high-scale scalar sector 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 pseudo-Nambu-Goldstone boson of the spontaneously broken SO(6) custodial symmetry. The minimal setting has the same number of parameters as the SM and predicts new physics in the form of a heavy Z' as well as a light but close-to invisible dilaton.

Speaker: Andreas Trautner

Trautner_Custodial_Naturalness_CERN_24.pdf

11:55 Scalar sector of CP4 3HDM

CP4 3HDM is a three-Higgs-doublet model based on the CP symmetry of order 4 (CP4) without any accidental symmetries. When exploring the scalar sector phenomenon of this model, the usual scan procedure is computationally time-consuming and inefficient. A much better scanning procedure, which we call the inversion, is to identify a set of crucial physical observables, to use them as input parameters, and to reconstruct the coefficients in the potential. In this work, we construct inversion in the scalar sector of CP4 3HDM.

Speaker: Bei Liu

CP4 scalar masses.pdf

12:35 → 14:30 Lunch

14:30 → 16:10 Contributed Talks

Convener: Andreas Trautner

14:30 Complex S_3 Symmetric 3HDM

We discuss a three-Higgs-doublet model with an underlying S3 symmetry, allowing in principle for complex couplings. In this framework it is possible to have either spontaneous or explicit CP violation in the scalar sector, depending on the regions of parameter space corresponding to the different possible vacua of the S3 symmetric potential. We list all possible vacuum structures allowing for CP violation in the scalar sector specifying whether it can be explicit or spontaneous. It is by now established that CP is violated in the flavour sector and that the Cabibbo-Kobayashi-Maskawa matrix is complex. In order to understand what are the possible sources of CP violation in the Yukawa sector we analyse the implications of the different available choices of representations for the quarks under the S3 group. This classification is based strictly on the exact S3-symmetric scalar potential with no soft symmetry breaking terms. The scalar sector of one such model was explored numerically. After applying the theoretical and the most important experimental constraints the available parameter space is shown to be able to give rise to light neutral scalars at the O(MeV) scale

Speaker: Margarida Nesbitt Rebelo (CFTP/IST/U. Lisboa)

mnrExtendedScalarsCERN21Oct24.pdf

14:50 Reconstructing the general 2HDM charged Higgs boson at the LHC

We study the discovery prospects for a charged Higgs boson via the $b g\to c H^- \to c \bar t b$ process at the Large Hadron Collider (LHC). Focusing on the general Two Higgs Doublet Model (G2HDM) that possesses extra Yukawa couplings, the process is controlled by extra top couplings $\rho_{tc}$ and $\rho_{tt}$, which can drive electroweak baryogenesis to account for the baryon asymmetry of the Universe. We propose benchmark points and demonstrate that evidence could emerge at 14 TeV LHC and luminosity of 300 fb$^{-1}$, with discovery potential at 600 fb$^{-1}$.

Speaker: Mohamed Krab (National Taiwan University)

G2HDM_CERN_Krab.pdf

15:10 Unlocking the 2HDM Phase Space: Recent Experimental Insights and Discovery Potential

This talk provides an overview of the direct searches for Beyond Standard Model (BSM) neutral heavy Higgs bosons conducted by the CMS experiment, focusing on both fermionic and bosonic decay channels. These searches are interpreted within the framework of the Two-Higgs-Doublet Model (2HDM), exploring various types and parameter spaces of the model. The discussion will spotlight recent CMS experimental efforts, particularly those based on the latest Run 2 data. We will analyze significant findings, including any observed excesses or anomalies, to evaluate their potential implications for new physics. Additionally, the talk will explore the remaining phase space within the 2HDM, identifying potential opportunities for new discoveries.
Future directions for these searches will be outlined, focusing on the new strategies and goals of probing deeper into the BSM Higgs sector with the forthcoming data.

Speaker: Khawla Jaffel (University of Science and Technology of China (CN))

Unlocking the 2HDM Phase Space_ Recent Experimental Insights and Discovery Potential-6.pdf

15:30 Low mass resonance search in bb final state at the LHC

The current Large Hadron Collider (LHC) data shows no clear indication of new physics yet and only incremental improvements are anticipated in the foreseeable future. LHC has been constraining TeV scale physics but new physics could be hiding below the electroweak scale. There are well-motivated dark matter models which predict a light mediator, coupled with Standard Model (SM) fermions and dark matter. In particular, the light resonance is expected to decay dominantly into bb final state if the mass is O(10) GeV. A measurement for this kind of signature is challenging due to trigger requirements at the LHC. In this talk, I will discuss on probing these light resonances in bb final state using jet substructure techniques. I will also demonstrate strategies to improve the sensitivity by modifying trigger requirements at the LHC.

Speaker: Amit Adhikary

ALP_AmitAdhikary.pdf

15:50 Associate production of light scalars at the LHC

We investigate the associated production of light scalars at the Large Hadron Collider (LHC) within the framework of the Two Real Singlet Model (TRSM). This model extends the Standard Model by introducing two real singlets, which interact with Standard Model particles through their mixing with the Higgs boson. Our study focuses on the physics process 𝑝 𝑝 → 𝑉 ℎ2, where 𝑉 represents 𝑊± or 𝑍 bosons and ℎ2 is an additional scalar in the model. The final state of this process consists of four low 𝑝𝑇 b-jets and the leptonic decays of 𝑊±/𝑍 bosons. In our analysis, we consider scenarios where the masses of these additional scalars are less than the SM-like Higgs boson mass 𝑚ℎ = 125.09. Our findings are derived using standard collider phenomenology tools. We found that these low mass final states 4b-jet + 𝑙+𝜈𝑙, or 𝑙−𝜈𝑙, or 𝑙+𝑙− could be promising for shining light to new physics BSM at the LHC

Speaker: Aman Desai (University of Adelaide (AU))

extended_higgs_workshop_aman_october_2024.pdf

16:10 → 16:40 Coffee Break

16:40 → 17:40 Contributed Talks

Convener: Martin Gabelmann (DESY)

16:40 Explaining the 152 GeV di-photon excesses at the LHC via associated production

Recently, statistically significant excesses have been observed at the LHC in associated di-photon production (γγ + X) at around 152 GeV in the sidebands of SM Higgs analyses. They are most pronounced in the single-tau, missing-transverse-energy, four-jet and ⩾ 1ℓ+ ⩾ 1b-jet channels and compatible with associated production mechanisms for new Higgs bosons (such as Drell-Yan), leading to a significance of ≈ 4σ.
In this context, I will argue how such excesses can be explained within different new physics scenarios.

Speaker: Guglielmo Coloretti (University of Zurich (UZH) / Paul Scherrer Institute (PSI))

AssProd_Higgses2HDM@LHC_CERN.pdf

17:00 Exotic Higgs decay $h \to Z a$ in the final state of two muons and two $\tau$ leptons

Exotic Higgs decays are among the most promising areas to be explored at the High Luminosity Large Hadron Collider, given the unprecedentedly large amount of the Standard Model-like Higgs bosons that will be produced. In this context, we introduce a new search channel where a Higgs boson with a mass of 125 GeV decays to a Z boson and a light pseudoscalar (a), in the final state with two muons and two $\tau$ leptons ($ h\to Z a\to \mu\mu\tau\tau $). In the preliminary analysis, performed at a center-of-mass energy of $\sqrt{s}=$13 TeV, masses of the pseudoscalar boson between 3.5 and 30 GeV are probed, focusing on the kinematic region where the $ h\to Z a$ decay is on-shell. We analyze several collider variables to propose a suitable signal region and consider the different decay channels for the di-tau system, as sensitivity is strongly influenced by the $\tau\tau$ reconstruction efficiency. Model-independent limits are set at the 95$\%$ confidence level as a function of $m_a$. Upper limits are also established within the Axion-Like Particle (ALP) framework, based on a specific model motivated by the anomalous $g-2$ measurement.

Speaker: Dr Rosa María Sandá Seoane (Instituto de Física Teórica UAM-CSIC)

Slides-Sanda-Seoane.pdf

17:20 Potential enhancements in triple Higgs production in proton proton colliders

Triple Higgs production will allow us to probe the nature of the scalar potential in High energy physics directly. In particular, it will permit us to probe the quartic self coupling of the Higgs boson. In this talk we will discuss the prospects of measuring triple Higgs production in proton-proton colliders within and beyond the Standard Model (BSM) considering the final state in which each Higgs decays into a pair b bbar (six-b jet final state). Potential enhacements on the production cross section of this process in the context of model dependent and model independent scenarios will be discussed.

Speaker: Gilberto Tetlalmatzi-Xolocotzi (Siegen University)

CERN_Higgs.pdf

18:30 → 20:00 Welcome Drink

Tuesday 22 October

09:00 → 10:30 Invited Plenaries

Convener: Margarida Nesbitt Rebelo (CFTP/IST/U. Lisboa)

09:00 CP violation in extended scalar sectors

Speakers: Margarete Muhlleitner, Milada Margarete Mühlleitner

ExtScalSec2024.pdf

09:45 Higgs & CP at the LHC

Speaker: R D Schaffer (Université Paris-Saclay (FR))

rds-extended-20240829_v5.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:30 Invited Plenaries

Convener: Zhen Liu (University of Minnesota (US))

11:00 DM models with extended scalar sectors

Speaker: Dr Venus Keus (Dublin Institute for Advanced Studies (DIAS))

Bullet.mov

VKeus_Scalars24-CERN.pdf

Xenon1T.mov

11:45 Higgs and the dark sector sector searches at the LHC

Speaker: Efe Yigitbasi (Rice University (US))

HiggsAndDS_EfeYigitbasi_ExtendedScalars_22Oct2024.pdf

12:30 → 14:00 Lunch

14:00 → 15:40 Contributed Talks

Convener: Dr Venus Keus (Dublin Institute for Advanced Studies (DIAS))

14:00 Spontaneous CPV from several angles

I will address several different aspects of spontaneous CPV induced by a scalar singlet and its relevance for e.g. the strong CP problem, leptogenesis, leptonic CP violation in neutrino oscillations, etc.

Based on ongoing work and on:

• Dark-sector seeded solution to the strong CP problem
  e-Print: 2303.00705 [hep-ph]

• Scalar-singlet assisted leptogenesis with CP violation from the vacuum
  e-Print: 2211.00042 [hep-ph]

• Flavour and dark matter in a scoto/type-II seesaw model
  e-Print: 2204.13605 [hep-ph]

Speakers: Filipe Rafael Joaquim (Universidade de Lisboa (PT)), Henrique Brito Câmara

Joaquim ES 2024.pdf

Joaquim split.pdf

14:20 CP-violation in 2HDM facing future EDM and Collider Tests

In this talk, I will choose 2HDM with soft $Z_2$ symmetry as an example, to discuss its CP-violation facing future EDM and collider tests. Currently, a large CP-phase ~$\mathcal{O}(0.1)$ is still allowed in a narrow window around $\tan\beta\sim1$ due to the cancellation in the electron EDM, and thus the neutron EDM sets the strictest constraint on the phase. Future EDM experiments with differnet materials will be able to limit it to $\mathcal{O}(10^{-2})$ even the cancellation still appears. Another cancellation region with large $\tan\beta$ is limited by the Hg EDM, since in this region the relative theoretical uncertainties are small enough. Future collider tests are good complementary cross-checks on CP-violation in this model. We discuss the CP-violation in heavy neutral and charged scalar sectors at future $e^+e^-$ or $\mu^+\mu^-$ colliders.

Speaker: Dr Ying-nan Mao (Wuhan University of Technology)

Testing CP-violation in a Heavy Higgs Sector at CLIC

Two-Higgs-doublet model with soft CP violation confronting electric dipole moments and colliders

YNMAO_CPViolation_CERN.pdf

14:40 Natural Alignment and CP Violation Beyond the Standard Model

The current LHC Higgs data suggest that the couplings of the observed 125 GeV Higgs boson must be remarkably close to the Standard Model (SM) expectations. This implies that any Beyond-the-Standard-Model physics due to an extended Higgs sector must lead to the so-called SM alignment limit, where one of the Higgs bosons behaves exactly like that of the SM. In the context of the Two Higgs Doublet Model (2HDM), this alignment is often associated with either decoupling of the heavy Higgs sector or fine-tuning the parameters of the 2HDM potential. In the first part of my talk, I will review the Higgs symmetries required for achieving natural alignment without decoupling or fine-tuning. However, the exact imposition of these symmetries lead to CP conservation in the Higgs potential. In the second part of my talk, I will then show how CP violation could be maximised in this case by spontaneous, soft and explicit breaking of these symmetries, while maintaining agreement with LHC data and constraints on a non-zero electron electric dipole moment. Finally, if time permits, I will discuss the collider signatures for a 2HDM Higgs sector in the natural alignment limit, which dominantly lead to third-generation quarks in the final state, like 4 tops, and can serve as a useful observational tool during the last upgraded phase of the HL-LHC.

Speaker: Apostolos Pilaftsis (University of Manchester)

PILAFTSIS_CERN-Oct-2024.pdf

15:00 New scalars as Dark Matter induced by Baryogenesis

We live in a Universe with only matter and no antimatter and most theories of Baryogenesis imply that in the early Universe at temperatures above T > 160 GeV, all Standard Model states (but the W) had different numbers of particles and antiparticles. If there was a new symmetry in the dark sector and particles with quantum numbers in both the SM and the dark sector, then dark matter would also have an asymmetry which is directly related to the baryon asymmetry of the Universe. This is the well-known asymmetric dark matter scenario. However, most models of asymmetric dark matter are rather involved and/or hide some tunings. In this talk, I will present a new scenario that is simple, minimal, and consistent, featuring two new scalars: a SM singlet and a SM doublet, both charged under a new dark Z4 symmetry. We show that in this scenario dark matter abundance can be related to the baryon asymmetry. The dark matter necessarily needs to have M > 6 TeV, and while the scenario is already rather constrained, we show that the model will be definitely tested in a few years in direct detection experiments.

Speaker: Miguel Escudero Abenza (CERN)

Escudero_AsymmetricScalarDarkMatter.pdf

15:20 A viable model with extended scalar sector for neutrino, dark matter and EW baryogenesis

I would like to introduce a viable model with extended scalar sector which can explain neutrino mass, dark matter and baryon asymmetry of the Universe simultaneously, in the framework of radiative seesaw mechanism, WIMP dark matter and EW baryogenesis. We then discuss phenomenology of this model from all angles. After showing some benchmark points which can satisfy current experimental constraints, we discuss to test the model at various future experiments, such as EDM measurements, various flavor experiments, LHC and HL-LHC, future lepton colliders, gravitational wave observation, primordial blackhole searches etc.

Speaker: Prof. Shinya KANEMURA (Osaka University)

CERN_Oct2024_S.Kanemura.pdf

15:40 → 16:10 Coffee break

16:10 → 17:50 Contributed Talks

Convener: Dr Andreas Papaefstathiou (Kennesaw State University, GA, USA)

16:10 Charge-breaking opportunities for the early Universe

The hot early Universe must have lived through phase transitions around the electroweak epoch. Multi-Higgs models often possess scalar potentials which, at finite temperatures, exhibit several competing minima and may lead to phase transitions of peculiar nature. In this talk, I will show that there exists a regime in the two-Higgs-doublet model in which thermal evolution of the early Universe passes through an intermediate phase with a charge-breaking vacuum. This regime leads to a sequence of phase transitions and it can also be tested at colliders. I will also show that multi-Higgs-doublet models support phase transitions in which two neutral minima are separated by a charge-breaking bubble wall, with remarkable and yet unexplored cosmological consequences.

Speaker: Prof. Igor Ivanov (Sun Yat-sen University, Zhuhai, China)

Igor-Ivanov-CERN-2024.pdf

16:30 Electroweak Baryogenesis via Domain Walls in the N2HDM

Domain walls are a type of topological defects that can arise in the early universe after the spontaneous breaking of a discrete symmetry. This occurs in several beyond Standard Model theories with an extended Higgs sector such as the Next-to-Two-Higgs-Doublet model (N2HDM).

In this talk I will discuss the ingredients needed for the successful generation of a matter-antimatter asymmetry in the early universe using domain walls related to the singlet scalar of the N2HDM. I will first demonstrate the possibility of restoring the electroweak symmetry in the vicinity of the domain wall leading to an unsuppressed sphaleron rate inside the wall. I also discuss how domain walls in this model can generate CP-violating electroweak vacua localized on the vicinity of the wall which can provide the CP-violation condition for baryogenesis while naturally evading EDM constraints.

This mechanism has the advantage of being independent on the order of the electroweak phase transition as well as evade any EDM constraints on CP-violation.

Speaker: Mohamed Younes Sassi (2.Institute for theoretical Physics Hamburg)

CernWorkshop.pdf

16:50 Multi-Higgs production and the Electroweak Phase Transition through TRSM

Exploring the Higgs sector via multi-Higgs production searches is a main goal for run-3 and high-lumi LHC. Can these searches inform us about the electroweak phase transition and matter-antimatter asymmetry? We address this question in the context of the TRSM (Two-Real-Singlet Model), which has known benchmark points enhancing multi-Higgs production. We update the triple-Higgs production benchmark points to include refined perturbativity bounds and explore the type of electroweak phase transition that occurs in the early universe; whether continuous or the first-order discontinuous phase transition desired for matter-antimatter asymmetry. After presenting our work, I outline lessons on correlating the type of electroweak phase transition and the enhancement of di-Higgs or triple Higgs production, highlighting the importance of the theory's vacuum expectation value of today and the symmetries of the model.

Speaker: Osama Karkout (Nikhef National institute for subatomic physics (NL))

EWSB_HHH_CERN.pdf

17:10 Conformal Majoron-like models with supercooled phase transitions

We study supercooled first-order phase transitions in a wide class of conformal Majoron-like U(1) models that explain the totality of active neutrino oscillation data and feature testable signatures of Stochastic Gravitational Waves Background (SGWB) at the reach of both space and earth-based interferometers. We demonstrate that these models can produce a detectable GW signal in LISA and LIGO's O5 observing run, and are thus amenable to testing in a broad frequency range from mHz to 100~Hz. As a key point, We discuss the implications of the current LIGO-Virgo-Kagra (LVK) data in setting constraints on the mass scale of new scalars for the class of models under consideration.

Speaker: António Morais (Universidade de Aveiro)

FOPTs.pdf

17:30 Accidental Suppression of Wilson Coefficients in Higgs Coupling

Higgs couplings are essential probes for physics beyond the Standard Model (BSM), as the Higgs potential can be generically modified by new physics, particularly through the Higgs portal interaction $|H|^2\mathcal{O}$. These modifications influence Higgs interactions via dimension-6 operators of the form $\sim \left(\partial |H|^2\right)^2$ and $\sim |H|^6$, which are generally expected to be of comparable size. This paper discusses a phenomenon of accidental suppression, where the $|H|^6$ coupling is significantly smaller than $\left(\partial |H|^2\right)^2$. This suppression, arising from the truncation of the tree-level effective potential, lacks a clear symmetry explanation but persists in Higgs-portal and neutrino-portal couplings. We explore toy examples and a specific model--the Standard Model (SM) gauge singlet extension of the Standard Model--in detail, aiming to inspire further studies on additional instances of accidental suppression without symmetry explanations or a general framework to characterize such suppression. We also discuss future collider constraints on the Wilson coefficients of the two dimension-6 operators for various benchmark scenarios of the concrete model.

Speaker: Zhen Liu (University of Minnesota (US))

HiggsSuppression_SScalars_ZhenLiu_Oct2024.pdf

19:00 → 21:30 Workshop Dinner

GoogleMaps Link

our_menu.pdf

Screenshot_Map.png

Wednesday 23 October

09:00 → 10:30 Invited Plenaries

Convener: Howard Haber (University of California,Santa Cruz (US))

09:00 EW phase transitions and other connections to Cosmology

Speaker: Graham White (Southampton)

CERN2024_GW.pdf

09:45 Electroweak baryogenesis in non-minimal composite Higgs models

Speaker: Oleksii Matsedonskyi (TUM)

matsedonskyi_CERN_24_1.pdf

10:30 → 11:00 Coffee break

11:00 → 12:30 Invited Plenaries

Convener: Jana Schaarschmidt (University of Washington (US))

11:00 Higgs self-coupling and prospects for HH and HHH

Speaker: Carlo Pandini (Nikhef National institute for subatomic physics (NL))

H_HH_Pandini_Extended2024_conference1.pdf

11:45 Searches for light scalars in direct production and in h125->aa decays at the LHC

Speaker: Alexandre Nikitenko (Imperial College)

Scalars.pdf

12:30 → 14:00 Lunch

14:00 → 15:00 TH Colloquium

14:00 The Higgs Boson : From Theory to Experiment (TH Colloquium)

The discovery of the Higgs boson in July 2012 was the highlight of an incredible journey in High Energy Physics. The Higgs field was postulated as the minimal addition to the Standard Model (SM) fermion and gauge boson field content, allowing to provide masses to all known fundamental particle in a gauge invariant way.

The scale of these masses is given by the Higgs field vacuum expectation value and the hierarchy of masses is dictated by the couplings of these particles to the Higgs boson.

The Higgs boson mass was anticipated by precision electroweak measurements, and the LHC has now studied its production and decay rates in many different channels, finding amazing consistency with this picture.

Apart from being the only known fundamental spin zero particle, the Higgs boson has,several fascinating properties: its couplings are flavor diagonal even under the presence of arbitrary complex Yukawas, its mass is proportional to its self-coupling and the associated Higgs field vacuum expectation value is unstable under the presence of new heavy fermion or scalar sectors.
This implies some rigidity in the construction of natural extensions of the minimal Higgs picture, as well as some mystery regarding the scale of the Higgs vacuum expectation value.

I will discuss these questions, the efforts to go beyond the SM picture and
the relevant experimental program designed to study the properties of this fascinating particle and the associated Higgs field potential.

This talk is given as part of the "TH colloquia" seminar series -- see https://indico.cern.ch/event/1394014/

Speaker: Carlos E.M. Wagner (The University of Chicago)

Link to Colloquium

Wagner-CERNColloquium.pdf

15:00 → 15:30 Coffee Break

15:30 → 17:00 Invited Plenaries

Convener: Maria Cepeda (CIEMAT)

15:30 Bridging the gap: Requests from Theory To Experiment

Speaker: Georg Ralf Weiglein (Deutsches Elektronen-Synchrotron (DE))

ExtScalSec_TheoNeeds_24.pdf

16:15 Challenges and opportunities at Run3 and HL-LHC

Speaker: Frank Filthaut (Radboud University and Nikhef, Nijmegen (NL))

Challenges-opportunities.pdf

17:00 → 17:30 Coffee break

17:30 → 18:30 Contributed Talks

Convener: Ian Lewis (The University of Kansas)

17:30 Pair production of Higgs Bosons at NLO

Higgs-boson pairs are dominantly produced via gluon fusion at hadron colliders, i.e. via a loop-induced process. This process will constitute the first direct access to the trilinear Higgs self-interaction. In recent years the NLO QCD corrections involving the full top-mass dependence became available by means of numerical integrations, since analytical methods available so far are not capable to solve the two-loop integrals with up to five energy scales. I'll discuss the method we have adopted to achieve the results with a summary of the outcome, i.e. with the particular emphasis on the scheme and scale dependence of the virtual top mass that induces the dominant theoretical uncertainties at present. This method has recently been extended to the cases of neutral Higgs-boson pair production within the 2HDM. Finally, I'll provide an outlook on the extension of the method to the full electroweak corrections to the same process within the SM.

Speaker: Michael Spira (Paul Scherrer Institute (CH))

spira.pdf

17:50 Double Higgs Boson Production in Association of Jets in the Triplet Higgs Model at the LHC

This presentation offers new insights into double Higgs boson production accompanied by 2 and 3 jet events at the LHC within the framework of the Triplet Higgs Model. By integrating matrix elements into the parton-level Monte Carlo VBFNLO and utilizing Herwig 7 for parton shower matching, we provide a comprehensive analysis. Our study delves into the azimuthal angle correlations between tagged jets. The impact of parton shower matching is discussed.

Speaker: Terrance Figy (Wichita State University)

ExtendedScalars-TFigy-Presentation.pdf

ExtendedScalars-TFigy-Presentation.pptx

18:10 Interference effects in resonant di-Higgs production at the LHC

In this talk I will present an investigation into finite width and interference effects in di-Higgs production at the LHC. I will focus on the real Higgs singlet extension of the Standard model where di-Higgs production is enhanced by resonant decays of an additional heavy scalar into two SM-like Higgs bosons. The study focuses on the effect of the interference between non-resonant and resonant diagrams and finds this to have a non-negligible effect on the cross-sections and differential distributions at the LHC. I will also present a new tool utilizing a matrix-element reweighting method allowing interference effects to be modelled in a computationally efficient way.

Speaker: Daniel Winterbottom (Imperial College (GB))

HH_inteference_scalarsworkshop.pdf

Thursday 24 October

09:00 → 10:30 Invited Plenaries

Convener: Lidija Zivkovic (Institute of physics Belgrade (RS))

09:00 Extended scalars and flavour

Speaker: Gudrun Hiller (Technische Universitaet Dortmund (DE))

ExtendedScalarsandFlavor2024-ghiller.pdf

09:45 Constraints on Extended Scalar Sectors from BPhysics at the LHC

Speaker: Biplab Dey (Eotvos U.)

LHCb_extHiggs.pdf

10:30 → 11:00 Coffee break

11:00 → 11:45 Invited Plenaries

Convener: Prof. Igor Ivanov (Sun Yat-sen University, Zhuhai, China)

11:00 Higgs&Flavour: Searches for H->cc, lfv and lighter fermions at the LHC

Speaker: Yusheng Wu (University of Science and Technology of China (CN))

Higgs and Flavor - Y. Wu - vF.pdf

Higgs and Flavor - Y. Wu - vF.pptx

11:45 → 12:30 Contributed Talks

11:45 Looking for a SFOEWPT in the RxSM at the HL-LHC and LISA

We explore the real-singlet extension of the Standard Model without a Z2 symmetry (RxSM), as a model to reconstruct the Higgs potental and explain the baryon asymmetry of the Universe. First, we determine regions of parameter space that allow a Strong First-Order Electroweak Phase Transition (SFOEWPT) using the public tools CosmoTransitions and TransitionListener, including also relevant theoretical constraints as well as experimental constraints using HiggsTools. Then, we compute the one-loop corrections to the trilinear Higgs couplings that enter di-Higgs production (hhh and hhH) using the public code anyH3. Finally, we compute the di-Higgs production cross section at the (HL-)LHC in the regions of the RxSM parameter space allowing a SFOEWPT, taking into account the one-loop corrections to the trilinear Higgs couplings. We compare this new result with the results in the SM and in the RxSM at tree level, highlighting the impact of the loop corrections to the trilinear couplings.

Speaker: Alain Verduras Schaeidt (DESY)

AVS_ExtendedScalars.pdf

12:05 Impact of Loop Corrections to the Trilinear Higgs Couplings and Interference Effects on Experimental Limits

We investigate the reliability of a comparison between the experimental results and the theoretical predictions for the pair production of the 125 GeV Higgs boson at the LHC. Recent experimental results for di-Higgs production provide already sensitivity to triple Higgs couplings (THCs) in models beyond the Standard Model (BSM). In our analysis within the Two Higgs Doublet Model (2HDM) we find that potentially large higher-order corrections to the trilinear couplings and the interference effects arising from additional heavy states have a strong impact on the expected shape of the differential cross section and the value of the total cross section. Both effects have to be taken into account for a correct interpretation of the experimental results. In particular, we demonstrate that neglecting the interference of the contributions of heavy Higgs resonances with non-resonant (background) diagrams, as done by the experimental collaborations, can lead to unreliable exclusion limits.

Speaker: Kateryna Radchenko Serdula (DESY)

Radchenko_ExtScalars.pdf

12:30 → 14:00 Lunch

14:00 → 14:45 Invited Plenaries

Convener: Santeri Laurila (CERN & Helsinki Institute of Physics (FI))

14:00 Lessons from recasting

Speaker: Sabine Kraml (LPSC Grenoble)

LessonsFromRrecasting-SKraml-ExtScalars2024.pdf

14:45 → 16:00 Contributed Talks

14:45 Impact of interference effects on Higgs searches in the di-top final state at the LHC

Various extensions of the Standard Model predict the existence of additional Higgs bosons. If these additional Higgs bosons are sufficiently heavy, an important search channel is the di-top final state. In this channel, interference contributions between the signal and the corresponding QCD background process are expected to be important. If more than one heavy scalar is present, besides the signal-background interference effects associated with each Higgs boson also important signal-signal interference effects are possible. We perform a comprehensive model-independent analysis of the various interference contributions within a simplified model framework considering two heavy scalars that can mix with each other, taking into account large resonance-type effects arising from loop-level mixing between the scalars. The interference effects are studied with Monte Carlo simulations for the di-top production process at the LHC. We demonstrate that signatures can emerge from these searches that may be unexpected or difficult to interpret.

Speaker: Romal Kumar

20241024_romal_cern.pdf

15:05 On the robustness of the indirect determination of the width of the detected Higgs boson

Experimental collaborations at the LHC provide indirect measurements of the total width of the discovered Higgs boson, assuming that on-shell coupling modifiers remain unchanged in the off-shell regime. However, new physics effects from realistic models with extended scalar sectors could invalidate this assumption and challenge the robustness of the indirect total width measurement. We investigate specific cases where an additional scalar appears as a resonance or at loop level in the $gg \rightarrow ZZ$ channel, including interference effects with the SM Higgs. Our results indicate that the phenomenological impact of such new physics effects on the total width measurement is generally small, except in certain parameter regions which can nonetheless be constrained from beyond the Standard Model analyses searching for extra scalars.

Speaker: Panagiotis Stylianou

Stylianou_ExtScalSectors.pdf

15:25 Sensitivity of 2HDMa searches to Inert Doublet Model

Recasting is an extremely powerful tool to derive limits on new physics models. With so many NP models at our disposal, recasting makes it easy to use the limits derived on certain models by experimental searches, to constrain any model of our choice. However, this method can fail, if the model of our interest not only differs from the one it is being recasted from, in terms of event rates, but also leads to significantly different final state kinematics. In such cases, the experimental search, optimized for a specific model may become completely insensitive to the new model under study. A dedicated search would then be necessary to probe interesting regions of the new model. We present such a case for DM models, namely Inert Doublet Model with di-lepton+MET final state and its recasting from 2HDMa, using ATLAS full run-2 data.

Speaker: Dr Jayita Lahiri (II. Theoretical Institute for Physics, University of Hamburg)

talk_IDMRecast_Lahiri.pdf

16:00 → 16:10 Group Photo

16:10 → 16:30 Coffee break

16:30 → 17:30 Discussion session

Convener: Tania Natalie Robens (Rudjer Boskovic Institute (HR))

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Friday 25 October

09:00 → 10:30 Invited Plenaries

Convener: Heidi Angelika Rzehak

09:00 Renormalization of extended scalar sectors

Speaker: Johannes Braathen (DESY)

Braathen_Scalars@CERN2024_final.pdf

09:45 EFT for Higgs

Speaker: Samuel Homiller (Harvard University)

241025_cern_scalars_efts_homiller_nobuilds.pdf

10:30 → 11:00 Coffee break

11:00 → 11:45 Invited Plenaries

Convener: Daniel Winterbottom (Imperial College (GB))

11:00 Higgs Combinations & EFT interpretations

Speaker: Nan Lu (University of Science and Technology of China (CN))

Hcomb_EFT_ATLAS_CMS_v3.pdf

11:45 → 12:30 Contributed Talks

11:45 Dissecting multi-Higgs production in new physics models

In this talk I will explore the behaviour of multi-Higgs boson production, with a focus on triple Higgs boson production, in the context of various new physics models. I will discuss theories that incorporate higher-dimensional operators, and models with one or two additional singlet scalar fields.

Speaker: Dr Andreas Papaefstathiou (Kennesaw State University, GA, USA)

ExtendedScalars_CERN_Oct2024.pdf

12:05 Decoding the Georgi-Machacek Scenario: Insights from the LHC and Future Possibilities

The Georgi-Machacek scenario, introducing a complex and a real scalar triplet as additional components of the electroweak symmetry breaking sector, enables substantial triplet contributions to the weak gauge boson masses, subject to the equality of the complex and the real triplet vacuum expectation values (vev) via a custodial SU(2) symmetry. The magnitude of this triplet vev strongly depends on the mass hierarchy in the scalar particle spectrum of the model. It is found that some constraints get relaxed, and the phenomenological potential of the scenario is more diverse, if the doubly charged scalar in the spectrum can decay not only into two like-sign $W$'s but also into one or two singly charged scalars. Moreover it has been noticed that, besides the charged scalars, the neutral scalars can also provide a spectacular signal at the LHC via the $\gamma\gamma$ mode. This $\gamma \gamma$ channel has been explored in detail taking into account the irreducible backgrounds as well as fakes. It has been pointed out that substantial regions of the GM parameter space is accessible to LHC studies, both at the high-luminosity run with $\int {\cal L} dt = 3000 fb^{-1}$, and also in Run-3 with $\int {\cal L} dt = 300 fb^{-1}$, even after folding in systematic errors. especially when analysis based on neural network is performed.

Speaker: Ms Rituparna Ghosh (Indian Institute of Science Education and Research, kolkata)

RG_ExScalar_CERN_2024.pdf

12:30 → 14:00 Lunch

14:00 → 15:00 Contributed Talks

Convener: António Morais (Universidade de Aveiro)

14:00 Searching for light new scalars with atomic and nuclear clocks

In recent years, the field of precision spectroscopy has emerged as a powerful and versatile probe for light new physics ranging from $10^{-22}$ eV to the MeV scale. In this talk I will focus on recent improvements of isotope shift measurements in ytterbium and on the first ever laser excitation of a nuclear transition, which was achieved earlier this year in thorium-229. Both have implications for the search for new scalars while allowing us to gain new insights into nuclear physics.

Speaker: Fiona Kirk (Physikalisch-Technische Bundesanstalt (DE))

presentation_CERN.pdf

14:20 Minimal U(1) two-Higgs-doublet models for quark and lepton flavour

In this talk I will discuss our recent paper 2406.03331 [hep-ph] where we study the minimal 2HDM with U(1) flavour symmetries which account for the observed pattern of quark and lepton masses and mixings. The corresponding phenomenology related to flavour processes in both sectors will also be investigated, as well as the constraints imposed in the parameter space. We show that, in some cases, Abelian flavour symmetries provide a natural framework to suppress flavour-changing neutral couplings and lead to scenarios featuring heavy neutral/charged scalar masses below the TeV scale within the reach of current experiments.

Speaker: Henrique Brito Câmara

HBCâmara_CERN_2024_Talk.pdf

14:40 Flavor-nondiagonal neutral Higgs Yukawa couplings revisited

In the most general two-Higgs doublet model, flavor-nondiagonal neutral Higgs couplings to fermions are present. Experimental constraints on flavor-changing neutral currents imply that such flavor-nondiagonal couplings must either be absent or significantly suppressed. One possible suppression mechanism proposed many years ago by Cheng and Sher relates the suppression of off-diagonal neutral Higgs couplings to the hierarchy of fermion masses and the corresponding suppression of CKM mixing angles. In this talk, the ansatz proposed by Cheng and Sher is revisited in light of the most recent CKM mixing angle data and the approximate Higgs alignment limit implied by the LHC Higgs data (in which the observed Higgs boson couplings are close to the corresponding Standard Model predictions).

Speaker: Howard Haber (University of California,Santa Cruz (US))

Haber_Revisit.pdf

15:00 → 15:30 Coffee break

15:30 → 16:50 Contributed Talks

Convener: Johannes Braathen (DESY)

15:30 Renormalization of the general Two-Higgs-Doublet Model

The Two-Higgs-Doublet Model (THDM) is one of the simplest and most extensively studied extensions of the Standard Model of particle physics (SM). It offers a rich phenomenology, and can, depending on the region in parameter space, address phenomena such as the observed matter-antimatter asymmetry in the universe and dark matter, which cannot be fully explained by the SM.

When computing perturbative predictions for observables in the THDM (or any given QFT model), the choice of renormalization scheme should have no effect on all-order results. However, due to the truncation of the perturbation series, this choice affects the properties of finite-order predictions, such as gauge (in)dependence and perturbative stability. Therefore, it is valuable to study and compare different renormalization schemes with the goal of optimizing for such properties.

In this talk, we will give a brief description of the general THDM and explain the renormalization procedure we performed. Different renormalization schemes will be applied and compared.

Speaker: Robin Feser

Renormalization_of_the_general_THDM.pdf

15:50 Precise predictions for trilinear Higgs couplings and $gg\to HH$

Investigating the trilinear self-coupling of the discovered Higgs boson is
one of the main goals of particle physics in the near and far future. At the same time the quest for the existence of Higgs-like self interactions also provides a unique possibility in the search for new physics. BSM states can modify the trilinear Higgs coupling at the classical- or quantum-level, or contribute resonantly to processes that are sensitive to its extraction (and combinations thereof). Gluon fusion into two SM-like Higgs bosons offers the most promising possibility to scrutinize and eventually disentangle such scenarios in the future.

In this talk, we will introduce the framework $\href{https://arxiv.org/abs/2305.03015}{\tt anyH3}$ which allows to compute trilinear scalar couplings at the full one-loop level in arbitrary renormalisable QFTs as well as its extension ${\tt anyHH}$ providing fully differential predictions for $gg\to h_i h_j$. The latter incorporates corrections proportional to BSM couplings at next-to-leading order to the resonant part of the process. We show that such corrections are crucial in BSM scenarios that feature an SM-like Higgs boson in exact alignment to the SM Higgs.
Finally, we present an extension of the SM-like trilinear Higgs self-coupling calculation to two-loops in arbitrary renormalisable QFTs - enabling the study of non-resonant Higgs pair production up to next-to-leading order in BSM couplings.

Speaker: Martin Gabelmann (DESY)

ESSFAA24.pdf

16:10 Two-loop form factors for Scalar Dark Matter annihilation to colored Standard Model particles

A UV complete model where the Dark Matter (DM) particle interacts with gluons via a colored scalar mediator provides a viable phenomenological model that can be tested at hadron colliders. While Mono-jet signatures are relevant for Collider searches, zero-jet processes would mean complete annihilation of Standard Model (SM) particles to DM particles, which contribute to relic-density of DM. We look at the DM annihilation to SM colored particles quarks and gluons which, at leading order, is a loop induced process in our model. We compute two-loop amplitudes in QCD which contribute to the process. Decomposing the amplitude in terms of Form factors and making use of the projector technique, scalar Feynman Integrals are obtained. Further, with the help of the IBP identities, an analytical expression for amplitude is obtained in terms of Master Integrals. The amplitude is made UV finite by Counterterm Renormalization. We will discuss results for the cases of small and large mass mediators. Our results can be used to predict DM pair production at hadron colliders and DM annihilation to SM colored particles at next-to-leading order in QCD.

Speaker: Warsimakram Imamsab Katapur

ExtendedScalarSectors_WIK.pdf

16:30 → 17:00 Closure

DSC_5072.JPG