Synthesis and coordination chemistry of 2-(di-2-pyridylamino)pyrimidine; structural aspects of spin crossover in an Fe(II) complex

This paper was accepted on February 26 20122-(Di-2-pyridylamino)pyrimidine (L), a potentially ditopic tetradentate ligand, was synthesized from commercially available di-2-pyridylamine and 2-chloropyrimidine. Despite being capable of bridging two metal atoms with bidentate chelation of both metal centres, L prefers to chelate or bridge through the more basic pyridyl donors of the di-2-pyridylamine moiety. Mononuclear trans-[Fe(NCS)2(L)2] and [Cu(L)2(H2O)](BF4)2•H2O complexes, and a discrete [Ag2(L)4](PF6)2 metallomacrocycle were isolated and structurally characterized by X-ray crystallography. A mononuclear palladium complex [PdCl2(L)]•(solvate), where solvate = ½H2O or CH2Cl2, was also readily obtained in 71% yield. One example of the ligand acting as a bis(bidentate) bridging ligand was observed in a dinuclear [(PdCl2)2(L)]•¾H2O complex that was obtained only in very low yield (ca. 3%) from the reaction that produced [PdCl2(L)]•½H2O. trans-[Fe(NCS)2(L)2] undergoes a temperature dependent HS-LS (HS = high spin; LS = low spin) crossover at ca. 205 K that was 2 observed by X-ray crystallography and magnetic measurements and attempts were made to understand the structural basis of this process. Despite efforts to isolate examples of L bridging two iron(II) centres, only the mononuclear trans-[Fe(NCS)2(L)2] species could be obtained.Rachel S. Crees, Boujemma Moubaraki, Keith S. Murray, and Christopher J. Sumb

Flavor structure of anomaly-free hidden photon models

Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the introduction of new chiral fermions. For flavor universal charges, couplings of the associated hidden photon to Standard Model fermions are flavor conserving at tree level. We show explicitly that even the flavor-specific charge assignments allowed by anomaly cancellation condition lead to flavor-conserving tree-level couplings of the hidden photon to quarks and charged leptons if the Cabibbo-Kobayashi-Maskawa or Pontecorvo-Maki-Nakagawa-Sakata matrix can be successfully reconstructed. Further, loop-induced flavor-changing couplings are strongly suppressed. As a consequence, the structure of the Majorana mass matrix is constrained and flavor-changing tree-level couplings of the hidden photon to neutrino mass eigenstates are identified as a means to distinguish the U(1)B−L gauge boson from any other anomaly-free extension of the Standard Model without new chiral fermions. We present a comprehensive analysis of constraints and projections for future searches for a U(1)B−L gauge boson, calculate the reach of resonance searches in B meson decays and comment on the implications for nonstandard neutrino interactions

Kination, meet Kasner: on the asymptotic cosmology of string compactifications

Abstract We study runaway, kination-dominated epochs in string cosmology. We show how the apparent classical decompactification runaway of the volume modulus, described by a kination epoch in the 4-dimensional EFT, can be uplifted to a classical Kasner solution in 10d in which the non-compact dimensions collapse towards a Big Crunch. This can also be generalised for arbitrary spacetime and compactification dimensions. We conclude with some comments on how this picture is modified by quantum effects, and the need for both dynamical and kinematical Swampland constraints

A study of Higgs CPCP properties using the Higgs Characterization Model and top associated production

This study utilises the Higgs Characterization model to investigate the CP properties of the Higgs coupling to the top quark using the $tH$ and $t\bar{t}H$ generation processes. This is done via simulations of proton-proton collisions with ATLAS detector conditions, which are calculated for seven different CP eigenstates using MadGraph5_aMC@NLO. Three orthogonal categories of cuts are subsequently implemented to find the cut efficiencies, which are used in conjunction with the cross-section to find the signal strength. Comparing the signal strength with experimental results shows that one cannot yet conclusively rule out any Higgs CP eigenstates. Analysing histograms showed that the most CP sensitive variables were the transverse momenta of the Higgs, leptons and photons, which showed a hardening as the Higgs coupling became CP odd

The Forward Physics Facility at the High-Luminosity LHC

International audienceHigh energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential

The Forward Physics Facility at the High-Luminosity LHC

International audienceHigh energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential