Supersymmetric μνSSM Model Impacts B Meson Decay

A theoretical study has investigated how new physics, specifically within the Supersymmetric Standard Model with neutrinos (μνSSM), influences the rare inclusive decay $B \to X_{\mathrm{s}} l^{+} l^{-}$. This decay is of particular interest because its rate and characteristics can be sensitive to particles and forces not accounted for in the Standard Model of particle physics. Researchers have identified the main contributions to the relevant Wilson coefficients, which are parameters describing the strength of interactions in the decay, and the particles associated with them within the μνSSM. The analysis focused on a systematic scan of the μνSSM parameter space, which allowed for the elucidation of the underlying physical mechanisms governing these dominant contributions. The obtained results are consistent with experimentally allowed regions, suggesting that the μνSSM could offer an explanation for potential future deviations observed in these decays. Experimental constraints from other relevant decays, such as $\bar{B} \to X_{\mathrm{s}}\gamma$, $B_{\mathrm{s}}^{0} \to \mu^{+} \mu^{-}$, and the 125 GeV Higgs boson mass, were also incorporated. A key part of the study was the systematic interference decomposition of the Wilson coefficient contributions to the forward-backward asymmetry (AFB). It was identified that the $C_7C_{10}$ and $C_9C_{10}$ interference terms are the dominant contributions governing the behavior of the AFB in both low- and high-$q^2$ (momentum transferred to the lepton pair) regions. Understanding these contributions is crucial for interpreting future measurements of the AFB, which is an observable sensitive to new physics and could reveal the existence of supersymmetric particles or other extensions of the Standard Model.

Re-evaluating Supersymmetry Limits with LHC Data

A new study has re-examined the constraints imposed by the Large Hadron Collider (LHC) on supersymmetry (SUSY), focusing on the electroweak-ino sector. Using public data from ATLAS Run 2 searches, researchers employed the SModelS v3.0 tool to reproduce and extend the original analysis, also incorporating results from the CMS experiment. This work is crucial for understanding which regions of the vast SUSY parameter space remain unexplored or are compatible with current observations. The ATLAS collaboration recently published an extensive scan of the phenomenological Minimal Supersymmetric Standard Model (pMSSM), with a particular focus on electroweak-inos, which are the supersymmetric partners of gauge and Higgs bosons. This scan aimed to determine how searches for electroweak production of SUSY particles in LHC Run 2 constrained this model. The simulation data (SLHA files) and the constraints from eight individual searches were made publicly available, allowing other research groups to validate and expand upon the results. The research team used this data to evaluate the capability of SModelS v3.0 to replicate the ATLAS constraints. Furthermore, they explored how the inclusion of CMS results alters the picture and what benefits are gained from the statistical combination of analyses from both experiments. The results underscore the need for a broad, multifaceted approach to maximize sensitivity and close loopholes in the extensive SUSY parameter space. The study also discusses the part of the parameter space with light electroweak-inos that remains valid despite the stringent LHC limits, indicating that supersymmetry is not ruled out, but its manifestations might be more subtle than anticipated.

Vector Dark Matter: Parametric Resonance Requires New Inflationary Conditions

A new study explores the viability of vector dark matter (VDM) production via parametric resonance in a Higgsed Abelian sector. This mechanism, which involves the amplification of a dark-Higgs field to generate VDM particles, critically depends on the initial displacement conditions of the dark-Higgs field. Researchers analyzed this problem using a calibrated nonlinear broad-resonance relic map and a stochastic inflationary analysis of the dark-Higgs condensate. The results show that a minimal light-spectator realization fails under standard inflationary duration. For broad resonance and isocurvature constraints to hold, an initial dark-Higgs field displacement of \( φ_0/H_I \gtrsim 3.3 imes10^4 \) is required, where \( H_I \) is the Hubble scale during inflation. However, stochastic equilibrium and finite-duration random walk only produce \( φ/H_I=\mathcal O(1) \). This large mismatch in initial displacement represents a robust, model-independent obstruction to the stochastic branch of VDM production. The study identifies a distinct, classically sourced branch where the condensate tracks a time-dependent minimum, \( φ_0=κH_*/\sqrt{λ_4} \), induced by a negative Hubble-induced mass. In this scenario, the radial fluctuation remains heavy during inflation. This sourced branch modifies the scaling relation of the dark matter particle mass, \( m_X \), from \( m_X\propto λ_4^{5/8}H_I^{-3/2} \) to \( m_X\propto κ^{-3/2}λ_4 H_*^{-3/2} \). The authors derived the simultaneous consistency conditions for this branch, including broad resonance, adiabatic tracking, perturbativity, sub-Planckian displacement, thermal non-erasure, spectator backreaction, and control of inflationary vector fluctuations. These findings suggest that Higgsed-vector resonance is not merely a dark matter production mechanism, but also a sensitive probe of the inflationary and reheating dynamics that determine its initial conditions. The work opens new avenues for exploring the connection between dark matter physics and early cosmological processes, potentially leading to tighter constraints on inflation models and the nature of dark matter.

Low-scale cosmological phase transitions and gravitational waves

A new study has investigated low-scale cosmological phase transitions within a dark Abelian Higgs sector, a gauge theory model describing spontaneous symmetry breaking. The work was motivated by recent evidence for a stochastic gravitational-wave (GW) background reported by pulsar timing array (PTA) collaborations. Researchers quantified the impact of thermal resummation, higher-order matching corrections, and higher-dimensional operators on the phase-transition thermodynamics and the resulting gravitational wave signal. Their analysis reveals that the parameter region favored by current PTA observations lies close to the boundary of validity of the effective field theory. In this regime, higher-dimensional operators become increasingly important. Despite substantial shifts induced by higher-order thermal corrections, the predicted signal from the model remains disfavored by PTA data, even within the controlled region of the theory. Furthermore, the study delineated parameter regions where the dark and visible sectors are thermally and hydrodynamically coupled or decoupled. It also revisited dark matter phenomenology, identifying asymmetric freeze-out as naturally compatible with both the observed relic abundance and the gauge couplings favored by strong phase transitions. These results underscore the importance of systematically controlled finite-temperature calculations for reliable GW predictions from low-scale cosmological phase transitions.

Chebyshev Approximations Improve Feynman Integral Calculations

A new method based on Chebyshev approximations promises to accelerate and simplify the calculation of Feynman integrals, essential mathematical tools for particle physics. This advance addresses one of the most significant computational challenges in collider physics, where prediction precision is crucial for interpreting experimental results from accelerators like the LHC. The technique exploits the analytic properties of these integrals to construct rapidly converging polynomial approximations along a path. The method introduces an adaptive approximation that dynamically samples the parameter space to optimize convergence. Implemented with double-precision arithmetic, it has demonstrated stability across the physical phase space, even in complex two-loop, five-point cases, which are representative of advanced quantum field theory calculations. One of its key advantages is the ability to handle spurious singularities with little to no manual intervention, a recurring problem in existing methods. This Chebyshev approximation proves competitive with state-of-the-art one-fold integral methods. By reducing computational complexity and time, this development could enable more precise and faster theoretical predictions for high-energy processes, facilitating the search for new physics beyond the Standard Model and the detailed characterization of known particles such as the Higgs boson.

Anadi Canepa, Spokesperson for the CMS Experiment at CERN

Italian physicist Anadi Canepa, a senior scientist at Fermilab, has been appointed spokesperson for the CMS (Compact Muon Solenoid) experiment at CERN. This appointment places her at the helm of one of the world's largest scientific collaborations, marking a significant milestone in high-energy particle physics. The CMS experiment is one of the two major detectors operating at the Large Hadron Collider (LHC) in Geneva, Switzerland. The CMS experiment is crucial for particle physics research, having played a fundamental role in the discovery of the Higgs boson in 2012, alongside the ATLAS experiment. Its primary objective is to explore the physics of the Standard Model and search for new physics beyond it, including the quest for supersymmetric particles, dark matter, and other fundamental interactions. The scale of the collaboration is reflected in the thousands of scientists and engineers from around the world who contribute to its design, construction, operation, and data analysis. The role of spokesperson involves coordinating the scientific and technical activities of the collaboration, as well as representing the experiment to the global scientific community and the public. This leadership is essential for maintaining the coherence and direction of such a large-scale project, ensuring that research objectives are met and that the results obtained are effectively communicated.

High-Scale Mirror Dark Matter and Primordial Gravitational Waves

A recent study explores a dark matter model based on a "mirror sector" of the Standard Model, interacting with ordinary matter solely through gravity. This mirror sector would possess the same symmetries as the conventional Standard Model, but with significantly higher energy scales and different couplings. The research focuses on how these differences, including distinct Yukawa couplings for the mirror Higgs boson and mirror fermions, would influence the early evolution of the universe. The authors predict that in this model, a dark phase transition would occur at high temperatures of the baryonic universe, much earlier than the ordinary Standard Model's electroweak phase transition. This transition could be first or second order, depending on the universe's scale and the Yukawa couplings. The case of a second-order phase transition is particularly interesting, as it could leave a detectable imprint on the spectrum of stochastic gravitational waves, a phenomenon potentially observable by future gravitational wave detectors. The work also examines the ability of this high-scale mirror dark matter to form atoms, showing that in certain scenarios it could have both atomic and subatomic components. An approximation of the total equation of state for this mirror dark matter is provided, and the study discusses how this model could reconcile seemingly contradictory observations from galaxy clusters like the Bullet Cluster and Abell 520, which suggest different dark matter properties at various scales.

The Number of Elementary Particles: 17 or Nearly a Thousand?

The question of how many elementary particles truly exist in the universe is more complex than it appears, with answers varying drastically from the 17 particles of the Standard Model to nearly a thousand. This disparity arises from different definitions of "elementary" and the inclusion of hypothetical particles predicted by theories beyond the Standard Model, such as supersymmetry or string theories. The search for a definitive answer is central to particle physics and the fundamental understanding of matter and forces. The Standard Model of particle physics describes 17 fundamental particles: six quarks (up, down, charm, strange, top, bottom), six leptons (electron, muon, tau, and their respective neutrinos), four force bosons (photon, gluon, W and Z bosons), and the Higgs boson. These particles have been experimentally observed and form the basis of our current understanding of matter and fundamental interactions. However, this model does not explain phenomena such as dark matter, dark energy, or gravity, suggesting the existence of additional, yet undiscovered particles. Theories such as supersymmetry (SUSY) propose that each Standard Model particle has a more massive "superpartner," effectively doubling the number of elementary particles. Other extensions, like string theories or those postulating extra dimensions, could introduce an even larger number of particles, including gravitons, axions, or dark matter particles. The existence of these hypothetical particles is the subject of intense research at accelerators like the LHC and in dark matter detection experiments, with the hope of resolving the inconsistencies of the Standard Model and unifying the fundamental forces.

New Constraints on R²-Higgs Inflation from ACT and SPT Data

Researchers have explored the R²-Higgs inflation model by incorporating nonminimal couplings of the Higgs field to the Ricci scalar. This analysis was conducted in light of recent observations from the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT). The study focuses on how dimension-four and dimension-six operators can influence the scalar spectral index (n_s), a key parameter describing primordial fluctuations in the early universe. The results indicate that the inclusion of dimension-six operators, specifically $|Φ|^2 R^2$ and $|Φ|^4 R$, can accommodate an enhanced n_s value, consistent with preferences from combined cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) analyses. Using a doubly covariant formalism, the team found that the same parameter space region explaining the observed n_s value can also induce rapid preheating through the production of Goldstone modes. This preheating mechanism could be crucial for efficient thermalization of the post-inflationary universe. The implication of this finding is significant, as efficient thermalization via this preheating mechanism could help match the inflationary energy scale with the CMB reference scale. This provides a vital link between theoretical inflation models and cosmological observations, offering a way to better understand the processes that occurred in the very first moments of the universe.