Search for: All records

$R$-parity can be extended to a continuous global $\mathrm{U}(1{)}_R$symmetry. We investigate whether an anomalous $\mathrm{U}(1{)}_R$can be identified as the Peccei-Quinn symmetry suitable for solving the strong $CP$problem within supersymmetric extensions of the Standard Model. In this case, $\mathrm{U}(1{)}_R$is broken at some intermediate scale and the quantum chromodynamics axion is the $R$-axion. Moreover, the $R$-symmetry can potentially be gauged via the Green-Schwarz mechanism within completions to supergravity, in order to evade the axion quality problem. Obstacles to realizing this scenario are highlighted and phenomenologically viable approaches are identified. Published by the American Physical Society2025 

A<sc>bstract</sc> Cosmology may give rise to appreciable populations of both particle dark matter and primordial black holes (PBH) with the combined mass density providing the observationally inferred value Ω_DM≈ 0.26. Early studies highlighted that scenarios with both particle dark matter and PBH are strongly excluded byγ-ray limits for particle dark matter with a velocity independent thermal cross section 〈σν〉 ~ 3 × 10⁻²⁶cm³/s, as is the case for classic WIMP dark matter. Here we examine the limits from di useγ-rays on velocity-dependent, including annihilations which arep-wave with 〈σν〉 ∝v²ord-wave 〈σν〉 ∝v⁴, which we find to be considerably less constraining. This work also utilizes a refined treatment of the PBH dark matter density profile. Importantly, we highlight that even if the freeze-out process isp-wave it is typical for (loop/phase-space) suppresseds-wave processes to actually provide the leading contributions to the experimentally constrainedγ-ray flux from the PBH halo. 

A bstract Electroweak baryogenesis (EWBG) offers a compelling narrative for the generation of the baryon asymmetry, however it cannot be realised in the Standard Model, and leads to severe experimental tensions in the Minimal Supersymmetric Standard Model (MSSM). One of the reasons for these experimental tensions is that in traditional approaches to EWBG new physics is required to enter at the electroweak phase transition, which conventionally is fixed near 100 GeV. Here we demonstrate that the addition of sub-TeV fields in supersymmetric extensions of the Standard Model permits TeV-scale strongly first-order electroweak phase transition. While earlier literature suggested no-go arguments with regards to high-temperature symmetry breaking in supersymmetric models, we show these can be evaded by employing a systematic suppression of certain thermal corrections in theories with a large number of states. The models presented push the new physics needed for EWBG to higher scales, hence presenting new parameter regions in which to realize EWBG and evade experimental tensions, however they are not expected to render EWBG completely outside of the foreseeable future experimental reach. 

Abstract The primary and secondary fragmentation dynamics of iodobenzene following its ionization at 120 eV were determined using three-dimensional velocity map imaging and covariance analysis. Site-selective iodine 4d ionization was used to populate a range of excited polycationic parent states, which primarily broke apart at the carbon-iodine bond to produce I⁺with phenyl or phenyl-like cations (C_nH ${{}_x}^{+}$or C_nH ${{}_x}^{2+}$, withn  =  1 – 6 andx  =  1 – 5). The molecular products were produced with varying degrees of internal excitation and dehydrogenation, leading to stable and unstable outcomes. This further allowed the secondary dynamics of ${\mathrm{C}}_6{\mathrm{H}}_x{}^{2+}$intermediates to be distinguished using native-frame covariance analysis, which isolated these processes in their own centre-of-mass reference frames. The mass resolution of the imaging mass spectrometer used for these measurements enabled the primary and secondary reaction channels to be specified at the level of individual hydrogen atoms, demonstrating the ability of covariance analysis to comprehensively measure the competing fragmentation channels of aryl cations, including those involving intermediate steps. 

Abstract Structural imaging of transient excited-state species is a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. However, separating the electronic and nuclear contributions to the spectroscopic observables is challenging, and typically requires the application of high-level theory. Here, we employ site-selective ionisation via ultrashort soft X-ray pulses and time-resolved Coulomb explosion imaging to interrogate structural dynamics of the ultraviolet photochemistry of carbon disulfide. This prototypical system exhibits the complex motifs of polyatomic photochemistry, including strong non-adiabatic couplings, vibrational mode couplings, and intersystem crossing. Immediately following photoexcitation, we observe Coulomb explosion signatures of highly bent and stretched excited-state geometries involved in the photodissociation. Aided by a model to interpret such changes, we build a comprehensive picture of the photoinduced nuclear dynamics that follows initial bending and stretching motions, as the reaction proceeds towards photodissociation. 

We describe an outreach event based on mathematics in the sea. 

We describe how to organize events such as Sonia Kovalevsky Days. 

We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot −1 ). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated. The angular distribution of the fragment ions is much more complex than in previously reported studies for triatomic polycations, and differs substantially between the two isomeric species. With support of simple simulations of the dissociation channels of interest, detailed physical insights into the fragmentation dynamics are obtained, including how the initial dissociation step in a sequential mechanism influences rovibrational dynamics in the metastable intermediate ion and how signatures of this nuclear motion manifest in the measured signals.