<p>We propose a novel class of dark matter (DM) candidates in the form of a heavy composite axionlike particle (ALP) with highly suppressed electromagnetic interactions populating vast yet unexplored domains in the ALP parameter space. This is achieved for the first time in the simplest dark confining gauge theory yielding a new composite glueball ALP (GALP) DM coupling-mass relation found in terms of two distinct fundamental scales—the large dark fermion mass scale and the dynamical scale of dark confinement. The presence of a heavy fermion portal between the visible (photons) and dark (GALPs) sectors ensures a strong radiative suppression of the GALP-photon coupling naturally without any fine-tuning. The observable features of heavy GALP DM in a minimal realization are controlled by only three physical parameters. Our work paves the road for a novel research field exploring the theory and phenomenology of composite ALPs in multimessenger astrophysics and cosmology.</p>

Sweden

Pierluca Carenza

Roman Pasechnik

China

Zhi-Wei Wang

Composite Heavy Axionlike Dark Matter

<p>We examine the vacuum stability of gauge symmetry breaking in five dimensions, compactified on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>S</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>/</mo><mo stretchy="false">(</mo><msub><mrow><mi mathvariant="double-struck">Z</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>×</mo><msubsup><mrow><mi mathvariant="double-struck">Z</mi></mrow><mrow><mn>2</mn></mrow><mrow><mo>′</mo></mrow></msubsup><mo stretchy="false">)</mo></mrow></math> orbifold. We consider <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SU</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Sp</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SO</mi><mo stretchy="false">(</mo><mn>2</mn><mi>N</mi><mo stretchy="false">)</mo></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>SO</mi><mo stretchy="false">(</mo><mn>2</mn><mi>N</mi><mo>+</mo><mn>1</mn><mo stretchy="false">)</mo></math> theories in the bulk, and provide an exhaustive classification of possible parity assignments that lead to stable orbifolds and of the corresponding symmetry breaking patterns. We use these results in the search for viable asymptotic grand unification theories (aGUT), testing the stability criteria on models based on SU(6) and SU(8). As a result, we identify two viable aGUTs: a unique SU(6) pathway down to the Standard Model, and one SU(8) model leading to an intermediate Pati-Salam partial unification.</p>

France

Denmark

Giacomo Cacciapaglia

South Africa

Alan S. Cornell

Aldo Deandrea

Wanda Isnard

Anca Preda

General vacuum stability of orbifold gauge breaking and application to asymptotic grand unification

In analysing five dimensional orbifolds with exceptional gauge groups, we seek to find stable vacua configurations which satisfy the minimal requirements for asymptotic grand unified models. In this respect we show that no minimal asymptotic grand unified theory can be built. Our results point towards non-minimal models based on $$E_6$$ : one featuring supersymmetry, and the other needing a modification of the Coleman–Weinberg potential to stabilise the breaking of $$E_6$$ to the standard model gauge group.

Alan Cornell

Are there minimal exceptional aGUTs from stable 5D orbifolds?

We study the Higgs boson decay into dark matter (DM) in the framework of freeze-in at stronger coupling. Even though the Higgs-DM coupling is significant, up to order one, DM does not thermalize due to the Boltzmann suppression of its production at low temperatures. We find that this mechanism leads to observable Higgs decay into invisible final states with the branching fraction of 10% and below, while producing the correct DM relic abundance. This applies to the DM masses down to the MeV scale, which requires a careful treatment of the hadronic production modes. For DM masses below the muon threshold, the Boltzmann suppression is not operative and the freeze-in nature of the production mechanism is instead guaranteed by the smallness of the electron Yukawa coupling. As a result, MeV DM with a significant coupling to the Higgs boson remains non-thermal as long as the reheating temperature does not exceed $$ \mathcal{O} $$ (100) MeV. Our findings indicate that there are good prospects for observing light non-thermal DM via invisible Higgs decay at the LHC and FCC.

Finland

Oleg Lebedev

Portugal

António Morais

Vinícius Oliveira

Invisible Higgs decay from dark matter freeze-in at stronger coupling

We study supercooled first-order phase transitions above the QCD scale in a wide class of conformal Majoron-like U(1)′ models that explain the totality of active neutrino oscillation data and produce a detectable stochastic gravitational wave background (SGWB) at LIGO, LISA and ET. We place constraints on the U(1)′ breaking scale and gauge coupling using current LIGO-Virgo-Kagra data. We find that strong supercooling can be ruled out in large regions of parameter space if a SGWB is not detected by these experiments. A null signal at LIGO and ET will disfavor a type-I seesaw scale above 10 GeV, while a positive signal is a signature of heavy right-handed neutrinos. On the other hand, LISA will be sensitive to seesaw scales as low as a TeV, and could detect a SGWB even if the right-handed neutrinos are decoupled.

João Gonçalves

United States

Danny Marfatia

Gravitational waves from supercooled phase transitions in conformal Majoron models of neutrino mass

We propose an extended Left-Right symmetric model with an additional global U(1) X  symmetry, which collapses to a residual subgroup ℤ 2 after spontaneous symmetry breaking. In this model, the light active neutrino masses are generated via a double seesaw mechanism with the Dirac submatrix arising at one loop. In addition, the masses of the charged fermions of the Standard Model (SM) that are lighter than the top quark are generated at one loop level and the residual ℤ 2 symmetry ensures the stability of the Dark Matter (DM) candidate of the model. To the best of our knowledge our model has the first implementation of the radiative double seesaw mechanism with the Dirac submatrix generated at one loop level. We show that the model can successfully account for the observed pattern of the SM fermion masses and mixing, and that it is compatible with constraints arising from the muon g-2 anomaly, neutrinoless double beta decay and DM.

Chile

Paulo Areyuna C.

A. Cárcamo Hernández

Vishnudath K. N.

Sergey Kovalenko

Iván Schmidt

Left-Right model with radiative double seesaw mechanism

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

Hannah Arnold

Germany

Duarte Azevedo

Croatia

Vuko Brigljevic

United Kingdom

Maggie Chen

Daniel Diaz

Javier Duarte

Netherlands

Tristan Pree

Jaouad Falaki

Dinko Ferencek

Pedro. Ferreira

Benjamin Fuks

India

Japan

Sanmay Ganguly

Osama Karkout

Marina Kolosova

Jacobo Konigsberg

Greg Landsberg

Canada

Bingxuan Liu

CERN

Switzerland

Brian Moser

Margarete Mühlleitner

Andreas Papaefstathiou

Tania Robens

Rui Santos

Brian Sheldon

Gregory Soyez

Marko Stamenkovic

Panagiotis Stylianou

Tatjana Susa

Gilberto Tetlalmatzi-Xolocotzi

Georg Weiglein

Giulia Zanderighi

Rui Zhang

HHH whitepaper

We study a simple extension of the Standard Model featuring a dark sector with an ultralight pseudo-Nambu-Goldstone boson as a dark matter candidate. We focus on the mass range <math><mrow><mi>O</mi><mo>(</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>20</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>, relevant for strong gravity applications, and explore its production and evolution in the early Universe. The model is formulated in such a way that dark matter does not couple directly to photons or other Standard Model particles avoiding some of the most stringent cosmological bounds related to axionlike particles. In this work, two different scenarios are considered depending on whether dark matter is produced in a preinflationary or postinflationary regime. We also discuss the effect from emergent topological defects such as cosmic strings and domain walls and estimate the spectrum of stochastic gravitational waves produced by their decay, enabling us to test the model at current and future gravitational-wave experiments.

António P. Morais

Brazil

António Onofre

Exploring the viability of a pseudo-Nambu-Goldstone boson as ultralight dark matter in a mass range relevant for strong gravity applications

We couple to group field theory (GFT) a scalar field that encodes the entanglement between manifold sites. The scalar field provides a relational clock that enables the derivation of the Hamiltonian of the system from the GFT action. Inspecting the Hamiltonian, we show that a theory of emergent gravity arises, and that this can be recast according to the Ashtekar’s formulation of general relativity. The evolution of the GFT observables is regulated by the Shrödinger equation generated by the Hamiltonian. This is achieved by imposing a renormalization group (RG) flow that corresponds to a simplified Ricci flow. As a consequence of the quantization procedure, the Hamiltonian is recovered to be non-Hermitian, and can be related to the complex action formalism, in which the initial conditions and the related future evolution of the systems are dictated by the imaginary part of the action.

Jinglong Liu

Stephon Alexander

Italy

Antonino Marcianò

A path integral formula of quantum gravity emergent from entangled local structures

We continue our work on the light-front formulation of quarkonium γ ∗ γ transition form factors, extending the formalism to J  PC  = 2++ tensor meson states. We present an analysis of γ ∗ γ → χ  c2 transition amplitude and the pertinent helicity form factors. Our relativistic formalism is based on the light-front quark-antiquark wave function of the quarkonium. We calculate the two-photon decay width as well as three independent γ ∗ γ transition form factors for J  z  = 0, 1, 2 as a function of photon virtuality Q 2. We compare our results for the two-photon decay width to the recently measured ones by the Belle and BES III collaborations. Even when including relativistic corrections, a very small Γ(λ = 0)/Γ(λ = 2) ~ 10 −3 ratio is found which is beyond present experimental precision. We also present the form factors as a function of photon virtuality and compare them to the sparse experimental data on the so-called off-shell width. The formalism presented here can be used for other 2++ mesons, excited charmonia or bottomonia or even light   <math> <mi>q</mi> <mover> <mi>q</mi> <mo>¯</mo> </mover> </math>  $$ q\overline{q} $$ -mesons.