The late-time cosmological expansion within a flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime is studied using a model characterized by bulk viscous dark matter (bulk viscosity $$\zeta = \zeta _0 \rho _m H^{-1}+\zeta _1 H $$ , $$\zeta _0$$ & $$\zeta _1$$ are constants, and $\textit{H}$, the Hubble parameter) interacting with a decaying vacuum density $$\rho _{\Lambda } = \mathcal {C}_0 + 3\nu H^2$$ , where $$\mathcal {C}_0$$ and $$\nu $$ are constants. The bulk viscous pressure is described by Eckart’s theory. The interaction term is defined as $$ Q=3H\alpha (\rho _m+\rho _\Lambda )$$ , where $$\alpha $$ , the interaction parameter. Analytical solutions for the Hubble parameter and the scale factor have been derived. The validity of the models is evaluated by constraining their free parameters using observational data from $\textit{Cosmic Chronometer}$, the $\textit{Pantheon}$, and a combination of both datasets. The goodness of fit is assessed by minimizing the $$\chi ^2$$ function utilizing the Markov Chain Monte Carlo (MCMC) method. Selection information criteria, namely AIC and BIC, have been obtained to analyze the models’ stability. Additionally, several essential cosmological parameters characterizing the evolution dynamics are estimated and discussed analytically, and compared with the $$\Lambda $$ CDM model. The proposed model suggests a transition from the deceleration to the acceleration phase, indicating thermodynamic equilibrium in the distant future, aligning with the $$\Lambda $$ CDM model. The model shows a slight deviation from $$\Lambda $$ CDM model and effectively reduces the $$H_0$$ tension between local measurements by $\textit{R}$21 and global measurements by Planck 2018. The model is consistent with thermodynamic laws and upholds the second law of thermodynamics. Finally, Phase-space analysis supports the same evolutionary transitional phases.

India

Tanmay Nandi

Amitava Choudhuri

Bulk viscous matter interacting with decaying vacuum energy density: a model for late-time evolution of the Universe

Scalar singlets under the Standard Model gauge group appear naturally in many well-motivated New Physics scenarios, such as the composite Higgs models. Unlike the Higgs boson in the Standard Model, they can induce large flavour-changing neutral currents (FCNCs) in the top sector. We investigate systematically the effects of a light scalar singlet $\textit{S}$ with top-quark FCNC couplings, by including the low-energy constraints from the $\textit{B}$ → $\textit{μ}$ decay, the muon anomalous magnetic moment ($\textit{g}$ − 2) and the neutron Electric Dipole Moment (EDM). We also perform a detailed Monte-Carlo simulation of the channel $\textit{pp}$ → $\textit{tS}$ + $\textit{j}$ with $\textit{S}$ → $\textit{μ}$ and $\textit{S}$ → $$ b\overline{b} $$ , and investigate the LHC sensitivity to the $\textit{tcS}$ couplings. It is found that the scalar singlet $\textit{S}$ can induce scalar-type contributions to the $\textit{B}$ $\textit{→ μ}$ decay, which do not suffer from the helicity suppression and contain a large CKM factor $$ {V}_{cs}^{\ast }{V}_{tb} $$ . As a result, constraints on the $\textit{tcS}$ couplings from the measured branching ratio $$ \mathcal{B} $$ ($\textit{B}$ → $\textit{μ}$ ) are quite stringent, being even stronger than the expected LHC sensitivity in some parameter spaces. Besides the CP-conserving $\textit{tcS}$ couplings, we have also considered the case of CP-violating $\textit{tcS}$ couplings, with $$ {y}_{R,L}^{ct}=\left|{y}_{R,L}^{ct}\right|{e}^{i{\theta}_{R,L}} $$ . It is found that the CP observables $$ {\mathcal{A}}_{\Delta {\varGamma}_s}^{\mu \mu} $$ and $$ {\mathcal{S}}_{\mu \mu} $$ of the $\textit{B}$ $\textit{→ μ}$ decay are sensitive to the phase $\textit{θ}$ , while the neutron EDM can provide bounds on the phase difference $\textit{θ}$ − $\textit{θ}$ . Therefore, they are complementary to each other in probing the CP phases of the $\textit{tcS}$ couplings.

China

Biao-Feng Hou

Xin-Qiang Li

Ya-Dong Yang

Xing-Bo Yuan

Ming-Wang Zhang

Phenomenological anatomy of top-quark FCNCs induced by a light scalar singlet

<p>Without invoking any cumulant determination at the input level, we present here the first calculations of direct estimates of the Lee-Yang zeros of the QCD partition function in (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-flavor QCD. These zeros are obtained in the complex isospin chemical potential <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> plane using the unbiased exponential resummation formalism on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>τ</mi></msub><mo>=</mo><mn>8</mn></math> lattices and with physical quark masses. For different temperatures, we illustrate the stability of the zeros closest to the origin from which we subsequently procure the radius of convergence estimates. From the temperature-dependence study of the real and imaginary parts of these zeros, we try estimating one of the possible critical points forming the second-order pion condensate critical line in the isospin phase diagram. Further, we compare these resummed estimates with the corresponding Mercer-Roberts estimates of the subsequent Taylor series expansions of the first three partition function cumulants. We also outline comparisons between resummed and Taylor series results of these cumulants for real and imaginary values of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> and highlight the behavior of different expansion orders within and beyond the obtained resummed estimates of the radius of convergence. We also reestablish that this resummed radius of convergence can efficiently capture the onset of the overlap problem for finite real <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> simulations.</p>

Germany

Sabarnya Mitra

Estimates of Lee-Yang zeros and a possible critical point on the pion condensate boundary in the QCD isospin phase diagram using an unbiased exponential resummation on the lattice

We compute next-to-leading power corrections in the zero-jettiness variable for the production of colorless final states at hadron colliders at next-to-leading order in QCD. To assess if the process-independence of leading power contributions can be extended, we attempt to construct generic expansions of phase spaces and matrix elements squared through next-to-leading power in the zero-jettiness. We highlight challenges associated with the collinear limit, where universality no longer holds at the subleading power, making the result process-dependent. We show that quantities that need to be calculated in the collinear limit can be obtained using Berends-Giele currents, enabling computation of power corrections to high-multiplicity final states. As a concrete example, we apply our method to compute power corrections in the zero-jettiness for lepton pair as well as multi-photon production in $$ q\overline{q} $$ collisions.

Prem Agarwal

Kirill Melnikov

Ivan Pedron

Philip Pfohl

Power corrections to the production of a color-singlet final state in hadron collisions in the $\textit{N}$-jettiness slicing scheme at NLO QCD

Certain supersymmetric elementary string states with angular momentum can be viewed as small black rings in a five-dimensional string theory. These black rings have zero area event horizon. The 4D-5D connection relates these small rings to small black holes without angular momentum in one less dimension. Recent works have proposed saddle solutions that compute the supersymmetric index for small black holes using gravitational path integral. In this paper, we propose an analogous saddle solution for a five-dimensional small black ring. The dominant contribution comes from a black ring saddle that rotates in both independent planes in five dimensions and has a finite area event horizon. We also write the saddle solution as a three center Bena-Warner solution.

Subhodip Bandyopadhyay

Gurmeet Punia

Yogesh Srivastava

Amitabh Virmani

The gravitational index of a small black ring

The freeze-in mechanism describes the out-of-equilibrium production of dark matter (DM) particles via feeble couplings or non-renormalisable interactions with large suppression scales. In the latter case, predictions suffer from a strong sensitivity to the initial conditions of the universe, such as the details of reheating. In this work, we investigate how this sensitivity is altered in the presence of a cosmological first-order phase transition. We show that freeze-in via non-renormalisable interactions is not always dominated by the highest temperatures of the Standard Model (SM) thermal bath, but instead may be governed by the period immediately after the phase transition, during which the decaying scalar field transfers its energy density to the SM radiation. We refer to this alternative production regime as $\textit{DM phase-in}$. Using numerical and approximate analytical solutions of the relevant Boltzmann equations, we determine the conditions under which phase-in or conventional freeze-in production dominates the final DM abundance in terms of the type of interaction between the DM and SM particles, the amount of supercooling before and the evolution of the scalar field after the phase transition. In the phase-in regime, the DM abundance is correlated with the peak frequency of the gravitational wave signal associated with the phase transition, opening up new observational possibilities.

Cristina Benso

Felix Kahlhoefer

Henda Mansour

Dark matter phase-in: producing feebly-interacting particles after a first-order phase transition

An important theoretical achievement of the last century was the realization that strict renormalizability can be a powerful criterion to select Lagrangians in the framework of perturbative quantum field theory. The Standard Model Lagrangian (without gravity) is strictly renormalizable from a perturbative point of view. On the other hand, the inclusion of gravity seems not to respect this criterion, since general relativity is perturbatively non-renormalizable. The aim of this work is to provide concrete evidence that strict renormalizability is still a valid criterion even when applied to gravity. First, we show that adding quadratic curvature terms to the Einstein-Hilbert action gives rise to a strictly renormalizable theory known as quadratic gravity. Second, we argue that this unique theory represents the most conservative approach to quantum gravity and, at the same time, is highly predictive, as it can explain new physics beyond general relativity already in the sub-Planckian regime. In particular, it provides one of the best fits to the CMB anisotropies via Starobinsky inflation and makes sharp cosmological predictions that can be tested in the near future. Finally, we comment on the (super-)Planckian regime and conclude with a historical note.

Netherlands

Luca Buoninfante

Strict renormalizability as a paradigm for fundamental physics

We introduce a new model for conditional and continuous data morphing called TRansport Adversarial Network for Smooth InTerpolation (TRANSIT). We apply it to create a background data template for weakly-supervised searches at the LHC. The method smoothly transforms sideband events to match signal region mass distributions. We demonstrate the performance of TRANSIT using the LHC Olympics R&D dataset. The model captures non-linear mass correlations of features and produces a template that offers a competitive anomaly sensitivity compared to state-of-the-art transport-based template generators. Moreover, the computational training time required for TRANSIT is an order of magnitude lower than that of competing deep learning methods. This makes it ideal for analyses that iterate over many signal regions and signal models. Unlike generative models, which must learn a full probability density distribution, i.e., the correlations between all the variables, the proposed transport model only has to learn a smooth conditional shift of the distribution. This allows for a simpler, more efficient residual architecture, enabling mass uncorrelated features to pass the network unchanged while the mass correlated features are adjusted accordingly. Furthermore, we show that the latent space of the model provides a set of mass decorrelated features useful for anomaly detection without background sculpting.

Switzerland

I. Oleksiyuk

S. Voloshynovskiy

T. Golling

TRANSIT your events into a new mass: fast background interpolation for weakly-supervised anomaly searches

We classify all the possible parity-invariant, non-Abelian couplings involving a partially massless spin-2 field and a pair of massless spin-3/2 fields around anti-de Sitter spacetime AdS . We re-derive a non-Abelian vertex recently found in [48] by Yu. M. Zinoviev following a different approach, and make explicit the structure of the non-Abelian gauge algebra, very similar to $$ \mathcal{N} $$ = 2 supergravity around AdS . We show that this vertex is obstructed at higher order in deformation, and that the graviton plus a vector gauge field are required to eliminate most, if not all, of the obstructions. The resulting gauge algebra produces all the structures of the super algebra $\textit{su}$(2$\textit{,}$ 2$\textit{|}$1), suggesting that the only consistent theory that couples a partially massless spin-2 field with massless gravitini is $$ \mathcal{N} $$ = 1 conformal supergravity expanded around AdS .

Belgium

Nicolas Boulanger

Guillaume Lhost

Sylvain Thomée

A note on partially massless supergravity

We study the radiative properties of a spherical and singularity-free black-hole geometry recently proposed in the literature. Contrary to the Schwarzschild spacetime, this geometry is geodesically complete and regular, and, instead of the singularity, it presents a minimal surface that connects a trapped (black-hole) with an antitrapped (white-hole) region. The geometry is characterized by two parameters: the Schwarzschild radius and another parameter that measures the area of the minimal surface. This parameter is related to certain corrections expected in the context of loop quantum gravity to the classical general-relativistic dynamics. We explicitly compute the spectrum of the Hawking radiation and the gray-body factor. Since the gravitational potential is shallower than in Schwarzschild, the emission spectrum turns out to be colder and purer (less gray). From this, we sketch the evaporation history of this geometry and conclude that, under certain assumptions, instead of completely evaporating, the black hole naturally leads to a remnant, which provides a possible resolution to the information-loss issue.

Spain

Asier Alonso-Bardaji

David Brizuela

Marc Schneider

Radiative properties of a nonsingular black hole: Hawking radiation and gray-body factor