We compute the real corrections to the impact factor for the production of a forward Higgs boson, retaining full top-mass dependence. We demonstrate that the rapidity divergence is the one predicted by the BFKL factorization and perform the explicit subtraction in the BFKL scheme. We show that the IR-structure of the impact factor is the expected one and that, in the infinite-top-mass approximation, the previously known result is recovered. We also verify that the impact factor vanishes when the transverse momenta of the t-channel Reggeon goes to zero, in agreement with its gauge-invariant definition, exploiting the m  t  → ∞ expansion up to the next-to-next-to-leading order.

Spain

Francesco Celiberto

Italy

Luigi Rose

France

Michael Fucilla

Gabriele Gatto

Alessandro Papa

The next-to-leading order Higgs impact factor at physical top mass: the real corrections

We show how effects of compositeness emerging in a Composite 2-Higgs Doublet Model can enter Standard Model (SM)-like Higgs boson pair production at the Large Hadron Collider in both resonant and non-resonant mode. Such effects can arise from modified trilinear Higgs self-couplings and top-Yukawa couplings, as well as from loops of new heavy quarks and additional quartic Higgs-fermion interactions. In the resonant case, significant distortions of the Breit-Wigner shape of a new scalar state decaying into the two SM-like Higgs states may occur due to interference effects amongst not only the SM-like diagrams but also those involving the new heavy quarks. In the non-resonant case, a modification of the underlying line-shape and a local maximum at twice a new heavy quark mass appear simultaneously. We quantify these effects by taking into account the relevant theoretical and latest experimental bounds.

Stefania Curtis

Germany

Felix Egle

Sweden

United Kingdom

Stefano Moretti

Margarete Mühlleitner

Japan

Poland

Kodai Sakurai

Composite 2-Higgs doublet model: strong effects on Higgs pair production

A precise modelling of the dynamics of bubbles nucleated during first-order phase transitions in the early Universe is pivotal for a quantitative determination of various cosmic relics, including the stochastic background of gravitational waves. The equation of motion of the bubble front is affected by the out-of-equilibrium distributions of particle species in the plasma which, in turn, are described by the corresponding Boltzmann equations. In this work we provide a solution to these equations by thoroughly incorporating the non-linearities arising from the population factors. Moreover, our methodology relies on a spectral decomposition that leverages the rotational properties of the collision integral within the Boltzmann equations. This novel approach allows for an efficient and robust computation of both the bubble speed and profile. We also refine our analysis by including the contributions from the electroweak gauge bosons. We find that their impact is dominated by the infrared modes and proves to be non-negligible, contrary to the naive expectations.

Andrea Guiggiani

Ángel Muyor

Giuliano Panico

Non-linearities in cosmological bubble wall dynamics

We show how to simplify the calculation of the finite contributions from heavy particles to EFT Wilson coefficients by using on-shell methods. We apply the technique to the one-loop calculation of g − 2 and Hγγ, showing how finite contributions can be obtained from the product of tree-level amplitudes. In certain cases, due to a parity symmetry of these amplitudes, the total contribution adds up to zero, as previously found in the literature. Our method allows to search for new natural zeros, as well as to obtain non-zero contributions in a straightforward way.

Benedict Harling

CERN

Alex Pomarol

Wilson coefficients and natural zeros from the on-shell viewpoint

First order phase transitions could play a major role in the early universe, providing important phenomenological consequences, such as the production of gravitational waves and the generation of baryon asymmetry. An important aspect that determines the properties of the phase transition is the dynamics of the true-vacuum bubbles, which is controlled by the density perturbations in the hot plasma. We study this aspect presenting, for the first time, the full solution of the linearized Boltzmann equation for the top quark species coupled to the Higgs field during a first-order electroweak phase transition. Our approach, differently from the traditional one based on the fluid approximation, does not rely on any ansatz and can fully capture the density perturbations in the plasma. We find that our results significantly differ from the ones obtained in the fluid approximation (including its extensions and modifications), both at the qualitative and quantitative level. In particular sizable differences are found for the friction acting on the bubble wall.

Bubble wall dynamics at the electroweak phase transition

The future 100 TeV FCC-hh hadron collider will give access to rare but clean final states which are out of reach of the HL-LHC. One such process is the Zh production channel in the   <math> <mfenced> <mrow> <mi>v</mi> <mover> <mi>v</mi> <mo>¯</mo> </mover> <mo>/</mo> <msup> <mi>ℓ</mi> <mo>+</mo> </msup> <msup> <mi>ℓ</mi> <mo>−</mo> </msup> </mrow> </mfenced> <mi>γγ</mi> </math>  $$ \left(v\overline{v}/{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-}\right)\gamma \gamma $$  final states. We study the sensitivity of this channel to the   <math> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>1</mn> </mfenced> </msubsup> <mo>,</mo> <mspace width="0.5em"></mspace> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>3</mn> </mfenced> </msubsup> <mo>,</mo> <mspace width="0.5em"></mspace> <msub> <mi>O</mi> <mi>φu</mi> </msub> </math>  $$ {\mathcal{O}}_{\varphi q}^{(1)},\kern0.5em {\mathcal{O}}_{\varphi q}^{(3)},\kern0.5em {\mathcal{O}}_{\varphi u} $$ , and   <math> <msub> <mi>O</mi> <mi>φd</mi> </msub> </math>  $$ {\mathcal{O}}_{\varphi d} $$  SMEFT operators, which parametrize deviations of the W and Z couplings to quarks, or, equivalently, anomalous trilinear gauge couplings (aTGC). While our analysis shows that good sensitivity is only achievable for   <math> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>3</mn> </mfenced> </msubsup> </math>  $$ {\mathcal{O}}_{\varphi q}^{(3)} $$ , we demonstrate that binning in the Zh rapidity has the potential to improve the reach on   <math> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>1</mn> </mfenced> </msubsup> </math>  $$ {\mathcal{O}}_{\varphi q}^{(1)} $$ . Our estimated bounds are one order of magnitude better than projections at HL-LHC and is better than global fits at future lepton colliders. The sensitivity to   <math> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>3</mn> </mfenced> </msubsup> </math>  $$ {\mathcal{O}}_{\varphi q}^{(3)} $$  is competitive with other channels that could probe the same operator at FCC-hh. Therefore, combining the different diboson channels sizeably improves the bound on   <math> <msubsup> <mi>O</mi> <mi>φq</mi> <mfenced> <mn>3</mn> </mfenced> </msubsup> </math>  $$ {\mathcal{O}}_{\varphi q}^{(3)} $$ , reaching a precision of |δg 1z | ≲ × 10 −4 on the deviations in the ZWW interactions.

Fady Bishara

Philipp Englert

Christophe Grojean

Switzerland

Marc Montull

Alejo Rossia

Precision from the diphoton Zh channel at FCC-hh

We study the dynamics of the Peccei-Quinn (PQ) phase transition for the QCD axion. In weakly coupled models the transition is typically second order except in the region of parameters where the PQ symmetry is broken through the Coleman-Weinberg mechanism. In strongly coupled realizations the transition is often first order. We show examples where the phase transition leads to strong supercooling lowering the nucleation temperature and enhancing the stochastic gravitational wave signals. The models predict a frequency peak in the range 100–1000 Hz with an amplitude that is already within the sensitivity of LIGO and can be thoroughly tested with future gravitational wave interferometers.

Michele Redi

Andrea Tesi

Gravitational waves from supercool axions

We study the occurrence of a strong first-order electroweak phase transition in composite Higgs models. Minimal constructions realising this scenario are based on the coset SO(6)/SO(5) which delivers an extended Higgs sector with an additional scalar. In such models, a two-step phase transition can be obtained with the scalar singlet acquiring a vacuum expectation value at intermediate temperatures. A bonus of the Nambu-Goldstone boson nature of the scalar-sector dynamics is the presence of non-renormalisable Higgs in- teractions that can trigger additional sources of CP violation needed to realise baryogenesis at the electroweak scale. Another interesting aspect of this scenario is the generation of gravitational wave signatures that can be observed at future space-based interferometers.

Composite dynamics in the early Universe

We consider a Composite Higgs Model (CHM) with two isospin doublet Higgs fields arising as pseudo Nambu-Goldstone bosons from a SO(6) → SO(4) × SO(2) breaking. The main focus of this work is to explicitly compute the properties of these Higgses in terms of the fundamental parameters of the composite sector such as masses, Yukawa and gauge couplings of the new spin-1 and spin-1/2 resonances. Concretely, we calculate the Higgs potential at one-loop level through the Coleman-Weinberg mechanism from the explicit breaking of the SO(6) global symmetry by the partial compositeness of fermions and gauge bosons. We derive then the phenomenological properties of the Higgs states and highlight the main signatures of this Composite 2-Higgs Doublet Model at the Large Hadron Collider, including modifications to the SM-like Higgs couplings as well as production and decay channels of heavier Higgs bosons. We also consider flavour bounds that are typical of CHMs with more than one Higgs doublet.

Kei Yagyu

A concrete composite 2-Higgs doublet model

In the framework of the (B − L) Supersymmetric Standard Model (BLSSM), we assess the ability of ground and space based experiments to establish the nature of its prevalent Dark Matter (DM) candidate, the sneutrino, which could either be CP-even or -odd. Firstly, by benchmarking this theory construct against the results obtained by the Planck spacecraft, we extract the portions of the BLSSM parameter space compliant with relic density data. Secondly, we show that, based on current sensitivities of the Fermi Large Area Telescope (FermiLAT) and their future projections, the study of high-energy γ-ray spectra will eventually enable us to extract evidence of this DM candidate through its annihilations into W + W − pairs (in turn emitting photons), in the form of both an integrated flux and a differential energy spectrum which cannot be reconciled with the assumption of DM being fermionic (like, e.g., a neutralino), although it should not be possible to distinguish between the scalar and pseudoscalar hypotheses. Thirdly, we show that, while underground direct detection experiments will have little scope in testing sneutrino DM, the Large Hadron Collider (LHC) may be able to do so in a variety of multi-lepton signatures, with and without accompanying jets (plus missing transverse energy), following data collection during Run 2 and 3.