The proposal of a rapid sign-switching cosmological constant in the late universe, mirroring a transition from anti-de Sitter (AdS) to de Sitter (dS) space, has significantly improved the fit to observational data and provides a compelling framework for ameliorating major cosmological tensions, such as the $\textit{H}$ and $\textit{S}$ tensions. An attractive theoretical realisation that accommodates the AdS → dS transition relies on the Casimir forces of fields inhabiting the bulk of a 5-dimensional (5-dim) set up. Among the fields characterising the dark sector, there is a real scalar field $\textit{ϕ}$ endowed with a potential holding two local minima with very small difference in vacuum energy and bigger curvature (mass) of the lower one. Shortly after the false vacuum tunnels to its true vacuum state, $\textit{ϕ}$ becomes more massive and its contribution to the Casimir energy becomes exponentially suppressed. The tunneling process then changes the difference between the total number of fermionic and bosonic degrees of freedom contributing to the quantum corrections of the vacuum energy, yielding the AdS → dS transition. We investigate the properties of this theoretical realisation to validate its main hypothesis and characterise free parameters of the model. We adopt the Coleman-de Luccia formalism for calculating the transition probability within the thin-wall approximation. We show that the Euclidean bounce configuration that drives the transition between $\textit{ϕ}$ vacua has associated at least a sixth order potential. We also show that distinctive features of the required vacuum decay to accommodate the AdS $\textit{→}$ dS transition are inconsistent with a 5-dim non-compact description of the instanton, for which the bounce is $\textit{O}$(5) symmetric, and instead call for a 5-dim instanton with a compact dimension, for which the bounce is $\textit{O}$(4) × U(1) symmetric.

United States

Luis Anchordoqui

Thailand

France

Ignatios Antoniadis

Daniele Bielli

Auttakit Chatrabhuti

Hiroshi Isono

Thin-wall vacuum decay in the presence of a compact dimension meets the $\textit{H}$

Exotic Higgs decays are among the most promising areas to be explored at the High-Luminosity LHC, given the unprecedentedly large amount (~ 3 × 10 ) of 125 GeV Higgs bosons that will be produced. In this context, we propose a new search channel for which the Higgs boson decays to a (leptonically decaying) $\textit{Z}$ boson and a light BSM pseudoscalar $\textit{a}$, which subsequently decays to a pair of $\textit{τ}$-leptons ($\textit{h}$ → $\textit{Za}$ → $\textit{ℓℓττ}$). After performing a validation of existing ATLAS and CMS exotic Higgs decay searches in related channels, we analyze the HL-LHC projected sensitivity of our $\textit{a → ττ}$ search, targeting the kinematic region where the exotic Higgs decay is two-body. We are able to probe pseudoscalar masses $\textit{m}$ ∈ [5$\textit{,}$ 33] GeV by leveraging both leptonic and hadronic $\textit{τ}$ decays, and establish model-independent 95% C.L. sensitivity projections on the branching fraction BR($\textit{h → Za}$) × BR($\textit{a → ττ}$). These $\textit{a → ττ}$ projections yield a competitive probe of light pseudoscalars, which depending on the model can become significantly more sensitive than projections from existing experimental searches in $\textit{a → μμ}$ and $\textit{a → γγ}$ final states. Finally, we explore the potential of our search to probe an Axion-Like-Particle (ALP) solution to the muon ($\textit{g −}$ 2) anomaly (when taken face-value), finding that our proposed $\textit{h → Za}$, $\textit{a → ττ}$ search can provide valuable constraints on such ALP scenario, in complementarity with existing $\textit{h → Za}$, $\textit{a → γγ}$ experimental searches.

Spain

M. Cepeda

J. No

Brazil

C. Ramos

R. Sandá Seoane

J. Zurita

Exotic $\textit{h → Za}$ Higgs decays into $\textit{τ}$ leptons

We study the new $Z'$ boson as a portal for the production of Higgs bosons $h_0$ and $H_0$ predicted by the Bestest Little Higgs Model through Higgs-strahlung processes $\mu^+\mu^- \to (Z, Z') \to Zh_0, ZH_0$ . We focus on the resonant and nonresonant effects of the $Zh_0, ZH_0$ signals. In our analysis, we consider the center-of-mass energies of $\sqrt{s}=3, 4, 6, 10, 30$ TeV and integrated luminosities of ${\cal{L}}=2, 4, 6, 10, 30$ ${ {\rm{ab}}^{-1}}$ projected for a future muon collider. The possibility of performing precision measurements for Higgs bosons $h_0$ and $H_0$ is very promising for the future muon collider. Furthermore, our results may be useful to the High Energy Physics community. Complementarily, we generate and provide the Feynman rules necessary for studying processes $\mu^+\mu^- \to (Z, Z') \to Zh_0, ZH_0$ .

J.M. Martínez-Martínez

A. Gutiérrez-Rodríguez

E. Cruz-Albaro

M.A. Hernández-Ruíz

New $\textit{Z}$' boson of the bestest little Higgs model as a portal to signatures of Higgs bosons $\textit{h}$ $_{0}$ and $\textit{H}$ $_{0}$ at the future muon collider

We study the Higgs couplings involved in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mi>h</mi></math> associated production mode at the Large Hadron Collider (LHC) in presence of Higgs-gauge boson coupling modifiers via <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>κ</mi></math> framework and dimension-six Standard Model (SM) effective theory operators. The analysis is performed mainly in the context of the High-Luminosity LHC (with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>14</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> and luminosity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3000</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>) setup using cut-based as well as machine learning techniques. The analysis shows significant betterment in the signal significance by using the machine learning technique. We also do a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>χ</mi><mn>2</mn></msup></math> analysis, which reveals an appreciable change in the sensitivity of the coupling modifiers due to the presence of effective operators, in particular, due to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>q</mi><mi>q</mi><mi>Z</mi><mi>h</mi></math> Higgs-current interactions. The dipole operators concerning the same vertex combine quarks of different chiralities and do not interfere with the SM diagrams, hence contributing only at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mi mathvariant="normal">Λ</mi><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo stretchy="false">)</mo></math>. In order to observe better sensitivity for this class of operators, we need to move to higher center-of-mass energy, where the effects of both Higgs-current and dipole four-point interactions are more prominent.

India

Subhaditya Bhattacharya

Sanjoy Biswas

Abhik Sarkar

Higgs couplings in SMEFT via <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>Z</mi><mi>h</mi></mrow></math> production at the HL-LHC

We investigate the LHC discovery prospects for a second Higgs doublet through <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> weak decay. The latter is identified as the smoking gun signature of two Higgs doublet models (2HDMs) with first-order electroweak (EW) phase transition, a necessary condition for EW baryogenesis. In the general 2HDM (G2HDM) that has flavor-changing neutral Higgs couplings, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math> may decay dominantly via <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover><mo>+</mo><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>c</mi></math> final states, giving rise to trilepton signals. By a phenomenological analysis, we show that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup><mi>t</mi><mover accent="true"><mi>c</mi><mo stretchy="false">¯</mo></mover></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mo>ℓ</mo><mo>+</mo></msup><msup><mo>ℓ</mo><mo>−</mo></msup><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>c</mi></math> final states could be a promising probe of G2HDM at the LHC with flavor violation.

Taiwan

Wei-Shu Hou

Mohamed Krab

Probing the general 2HDM with flavor violation through <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math>

Both ATLAS and CMS have recently performed the first searches for a heavy new spin-0 resonance decaying into a lighter new spin-0 resonance and a $\textit{Z}$ boson, where the lighter spin-0 resonance subsequently decays into $$ t\overline{t} $$ pairs. These searches are of particular interest to probe Two Higgs doublet model (2HDM) parameter space regions that predict a strong first-order electroweak phase transition. In the absence of CP violation, the investigated decay is possible if the lighter and the heavier spin-0 particles have opposite CP parities. The analysis techniques employed by ATLAS and CMS do not distinguish between the two possible signatures $\textit{A}$ → $\textit{ZH}$ and $\textit{H}$ → $\textit{ZA}$, where $\textit{A}$ and $\textit{H}$ denote CP-odd and CP-even Higgs bosons, respectively, if both signals are predicted to have the same total cross sections. We demonstrate the capability of angular variables that are sensitive to spin correlations of the top quarks to differentiate between $\textit{A}$ → $\textit{ZH}$ and $\textit{H}$ → $\textit{ZA}$ decays, even in scenarios where both signals possess identical total cross sections. Focusing on masses of 600 GeV and 800 GeV as a representative 2HDM benchmark, we find that a distinction between the two possible channels is possible with high significance with the anticipated data from the high-luminosity LHC, if the invariant mass distribution of the $$ t\overline{t} $$ system is further binned in angular variables defined by the direction of flight of the leptons produced in the top-quark decays. Moreover, we find a moderate gain in experimental sensitivity due to the improved background rejection for both signals.

Germany

Francisco Arco

Thomas Biekötter

Panagiotis Stylianou

Georg Weiglein

Top-quark spin correlations as a tool to distinguish pseudoscalar $\textit{A}$ → $\textit{ZH}$ and scalar $\textit{H}$ → $\textit{ZA}$ signatures in $$ Zt\overline{t} $$ final states at the LHC

The $\textit{H}$ → $\textit{γγ}$ decay is an ideal process to study the structure of next-to-leading power logarithms induced by quarks due to its simple initial and final states. We perform a region analysis of this process up to two-loop level to inspect the origins of the logarithms. To deal with the endpoint singularities that are prevalent for the next-to-leading power logarithms, we have adopted two different kinds of regulators to exhibit the advantages and disadvantages of each regulator. In the analytic regulator we have chosen, the power of the propagator is changed by $\textit{η}$. And the endpoint singularities are regulated in the form of 1/$\textit{η}$. These poles cancel between the collinear and anti-collinear sectors since there is no soft mode in such a regulator. In the ∆ regulator, the soft sector is important. The leading and next-to-leading logarithms can be inferred from only this sector. Moreover, the symmetry between the collinear and anti-collinear sectors is preserved. After imposing a cut on the bottom quark transverse momentum, the leading order result is finite in each sector. We also discuss the next-to-next-to-leading power contributions and find that the potential factorization formulae involve two-dimensional endpoint singularities. Our region analysis could help to develop sophisticated factorization and resummation schemes beyond leading power.

China

Jun-Yao Hou

Jian Wang

Da-Jiang Zhang

Region analysis of $\textit{H}$ → $\textit{γγ}$ via a bottom quark loop

Using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msub><mrow><mi>h</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow></math> decays from a data sample of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>27.12</mn><mo>±</mo><mn>0.14</mn><mo stretchy="false">)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>ψ</mi><mo stretchy="false">(</mo><mn>3686</mn><mo stretchy="false">)</mo></mrow></math> events collected by the BESIII detector at the BEPCII collider, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>h</mi><mi>c</mi></msub></math> radiative decays to multiple light hadrons below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.8</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math>—<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>η</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mn>2</mn><mo stretchy="false">(</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">)</mo></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mi>p</mi><mover accent="true"><mi>p</mi><mo stretchy="false">¯</mo></mover></math>—are observed for the first time, each with a significance greater than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>5</mn><mi>σ</mi></math>. The corresponding branching fractions are measured. Furthermore, intermediate states are investigated, leading to the first observation of the decay process of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>h</mi></mrow><mrow><mi>c</mi></mrow></msub><mo stretchy="false">→</mo><mi>γ</mi><msub><mrow><mi>f</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy="false">(</mo><mn>1270</mn><mo stretchy="false">)</mo><mo stretchy="false">→</mo><mi>γ</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> with a significance of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>5.1</mn><mi>σ</mi></math>. This observation represents the first instance of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>h</mi><mi>c</mi></msub></math> radiative decay to a tensor state.

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

JINR

O. Bakina

Y. Ban

H.R. Bao

Poland

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

R.A. Briere

A. Brueggemann

H. Cai

M.H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

Türkiye

S.A. Cetin

X.Y. Chai

J.F. Chang

G.R. Che

Y.Z. Che

G. Chelkov

C. Chen

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.L. Chen

S.M. Chen

T. Chen

X.R. Chen

X.T. Chen

Y.B. Chen

Y.Q. Chen

Z.J. Chen

South Korea

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

J.J. Cui

H.L. Dai

J.P. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denysenko

M. Destefanis

F. De Mori

B. Ding

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

Y.Y. Duan

Z.H. Duan

P. Egorov

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y.Q. Fang

R. Farinelli

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

Y.T. Feng

M. Fritsch

C.D. Fu

J.L. Fu

Y.W. Fu

Observation of Charmonium <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>h</mi></mrow><mrow><mi>c</mi></mrow></msub></mrow></math> Radiative Decays to Multiple Light Hadrons and the Tensor State <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>f</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy="false">(</mo><mn>1270</mn><mo stretchy="false">)</mo></mrow></math>

Motivated by a small but intriguing excess observed in the decay mode $\textit{H}$ → $\textit{ℓ}$ $\textit{ℓ}$ $\textit{γ}$ reported by both the ATLAS and CMS collaborations, we explore the possibility that new physics contributes directly to the effective $$ H\overline{\mathcal{ll}}\gamma $$ coupling rather than modifying the $\textit{Z}$ peak. Concretely, we consider a dimension-8 operator that could arise from new particles via box diagrams. Such non-resonant contribution may provide an alternative origin for current or future excesses. We examine how experimental cuts may distinguish between possible modifications of the $\textit{Z}$ peak and non-resonant contributions. The currently measured excess requires that the new physics scale is relatively low (Λ ~ $\textit{v}$). However, we show that it may remain within current experimental bounds. In particular, we illustrate this using a simplified model, motivated by the dark matter problem, and discuss its other experimental constraints.

Belgium

Aliaksei Kachanovich

Jean Kimus

Steven Lowette

Michel Tytgat

On new physics off the Z peak in $\textit{H → ℓ}$

The decay <math altimg='si1.svg'><mi>H</mi><mo stretchy='false'>&#8594;</mo><mi>Z</mi><mi>Z</mi><mo stretchy='false'>&#8594;</mo><mn>4</mn><mi>&#8467;</mi></math>, with <math altimg='si2.svg'><mi>&#8467;</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>e</mi><mo>,</mo><mi>&#956;</mi></math>, can be used to test quantum interference in analogy to the famous double-slit experiment. The observations corresponding to &#8216;covering a slit&#8217; can be extracted from data in the <math altimg='si3.svg'><mi>e</mi><mi>e</mi><mi>&#956;</mi><mi>&#956;</mi></math> channel, while the observations when both &#8216;slits&#8217; are open, which include the interference, are measured in the <math altimg='si4.svg'><mn>4</mn><mi>e</mi><mo stretchy='false'>/</mo><mn>4</mn><mi>&#956;</mi></math> channels. In this way, this process offers a unique opportunity to investigate identical-particle effects at high energies, and provides the first evidence of identical-particle behaviour for muons. Sensitivity at the 4 <italic>&#963;</italic> level could be achieved at the high-luminosity upgrade of the Large Hadron Collider.

J.A. Aguilar-Saavedra

<italic>H</italic>&#8239;&#8594;&#8239; <italic>ZZ</italic> as a double-slit experiment