Theorie Palaver

Axion-like particles (ALPs), the pseudo-Goldstone bosons arising from the spontaneous breaking of global symmetry, are promising contenders for dark matter. The most extensively studied ALP production mechanism is known as misalignment mechanism, where ALP is presumed to initially remain frozen at a point in the field space until it begins oscillating around the potential minimum and behaves as cold dark matter (CDM). The oscillation initiates once the universe Hubble expansion rate falls below the ALP mass, defining the oscillation frequency. In this work, we examine how electroweak symmetry breaking (EWSB) affects ALP evolution, specifically through a higher order Higgs portal interaction. The interaction is observed to contribute partially to the ALP's mass during EWSB, thus altering oscillation frequencies and influencing the correlation between the scale of symmetry breaking and its mass. The novelty of this study lies in broadening the parameter space satisfying correct CDM relic density, facilitating future exploration through a diverse range of experimental avenues.

Axion-like particles (ALPs) are compelling candidates for new physics and have been extensively studied across a broad mass range, from sub-eV to hundreds of GeV. In this talk, I will discuss our recent works on ALP phenomenology across various experiments. First, I will present the potential for detecting ultralight ALP dark matter through radio telescopes that capture radio signals from axion-photon resonant conversion in the solar corona. We analyse data of the high-sensitivity radio telescope LOFAR, which provides stringent constraints on ALP interaction, contributing to the growing landscape of dark matter searches. I will then turn to collider and beam dump experiments, where we investigate the concurrent effects of ALPs, focusing on how ALP-photon and ALP-electron interactions jointly influence the detection of ALPs and demonstrate how current experimental limits are modified.

Weak decays of heavy hadrons provide an excellent way to test the flavour and QCD structure of the SM. In this talk, I will present recent results and ongoing work on the study of both inclusive and exclusive decays, in both the beauty and charm sectors. Specifically, I will start by discussing the current status of the heavy quark expansion (HQE) and its application to the study of heavy hadron lifetimes. Then, I will describe the analysis of non-leptonic two body $B$- and $D$-meson decays using the framework of light-cone sum rules (LCSR), in light of the observed tensions in channels like $B^0 \to D^+ K^-$, and of the recent discovery of CP violation in the charm sector.

Supergravity solutions with orbifold singularities contribute non-trivially to the quantum gravity path integral, unveiling new holographic correspondences. These solutions relate to supersymmetric quantum field theories (QFTs) defined on orbifolds with conical singularities, whose partition functions capture crucial physical insights such as dualities between different models and the entropy of accelerating black holes. From a mathematical perspective, the path integrals of these theories link to topological invariants of the underlying orbifolds, extending known results from smooth manifolds to singular spaces. This talk will present an investigation into supersymmetric QFTs on orbifolds with conical singularities, focusing on general circle fibrations over spindles.

We systematically study potential effects of BSM physics in the e+ e- -> Z H process. To this end, we include all relevant dimension-6 Standard Model Effective Field Theory operators and work to next-to-leading order (NLO) accuracy in the electro-weak coupling. We consider both polarized and unpolarized electron and positron beams and present results for $\sqrt{s}$=240, 365 and 500~GeV and emphasize observables where the NLO predictions differ significantly from the leading order (LO) results. At NLO, a sensitivity arises to operators that do not contribute at tree level, such as the Higgs trilinear coupling , CP violating operators, dimension-6 operators involving the top quark or anomalous Higgs-Z boson couplings, among many others. We compare the prospects of future e+e- colliders to explore these new physics effects with measurements from the LHC, electron EDMs (for CP violating operators), and Z pole measurements.

With the measurements made by the experiments at the Large Hadron Collider becoming increasingly precise, it is vital that theoretical predictions reach the same level of precision, including for high multiplicity processes. This necessitates calculations to at least next-to-next-to-leading order (NNLO) in perturbative QCD. One of the challenges in computing such corrections is the treatment of infrared singularities, which arise at intermediate stages of the calculation. Although such singularities must cancel for physical observables, making this cancellation manifest while maintaining fully differential results is challenging, especially at NNLO where singularities from different kinematic limits may overlap in a complicated way. I will discuss the development of the nested soft-collinear subtraction scheme to regulate IR singularities and arrive at a finite physical result at NNLO. I will begin by outlining the method for the production of a color-singlet, and then discuss recent efforts to generalize it to arbitrary hadroproduction processes.

Future gravitational wave (GW) observatories offer an exciting opportunity to explore new physics at unprecedented energy scales. A prominent class of models predicting strong GW signals are quasi-conformal Standard Model (SM) extensions, which offer a mechanism for dynamically generating the electroweak (EW) scale. These models modify the thermal history of the Universe by a substantial period of thermal inflation that typically ends with a strong first-order phase transition. I will show that a large parameter exists where this scenario changes. Instead, QCD chiral symmetry breaking triggers a tachyonic phase transition, driven by classical rolling of a new scalar field sourcing EW symmetry breaking. As the field evolves through a regime where its effective mass is negative, long-wavelength scalar field fluctuations are exponentially amplified, preheating the supercooled Universe. This process generates a strong, unique GW background detectable by future experiments across nearly the entire viable parameter space.

Theoretical predictions beyond tree-level are necessary for a meaningful comparison between theory and experiment. Their calculation makes it inevitable to deal with infrared (IR) divergencies, stemming from partons becoming soft or collinear. One way to overcome them is to resort to subtraction schemes. In this talk, I will present the antenna subtraction scheme and the current efforts to extend it to N3LO, focusing on the situation where hard radiators are both in the initial and in the final state. First, I will review the extension of the N2LO initial-final antennae to higher epsilon order and present a purely analytic strategy to fix the boundary conditions of the relevant phase-space integrals (based on the Auxiliary Mass Flow method). Finally, I present the status of the calculation of N3LO initial-final antennae and the theoretical machinery necessary to perform this it, which includes translating phase space integrals into cuts of loop integrals, finding a canonical basis and fixing boundary conditions.

The Higgs potential appears fine-tuned, relating to the hierarchy problem, the metastability of the electroweak vacuum and, arguably, the cosmological constant problem. While such behavior is puzzling in conventional particle physics, it is a common feature of dynamical systems. This motivated the conjecture that the Higgs' parameters are set by some dynamical mechanism. In this talk, I will demonstrate how these ideas can be linked — in a mostly mechanism-independent way — to concrete phenomenological predictions that can be tested by realistic future experiments such as the FCC or next-generation GW detectors. Along the way, I will also highlight several lessons learnt for the construction of concrete vacuum selection mechanisms.

In this talk, a new physical basis and a Green’s basis for dimension-seven (dim-7) operators are proposed, which are suitable for the matching of ultraviolet models onto the Standard Model Effective Field Theory (SMEFT) and the deviation of renormalization group equations (RGEs) for the SMEFT dim-7 operators. The reduction relations to convert operators in the Green’s basis to those in the physical basis are achieved as well, where some redundant dim-6 operators in the Green’s basis are involved if the dim-5 operator exists. Working in these two bases, we work out the one-loop RGEs resulting from the mixing among different dimensional operators for the SMEFT dim-7 operators for the first time, and also revisit those from the mixing among dim-7 operators. These results complete the full one-loop RGEs of dim-7 operators and can be used for a consistent one-loop analysis of the SMEFT. On the other hand, we accomplish the full two-loop RGE of the dim-5 Weinberg operator and discuss its effects on the initially massless neutrino.