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Figueroa, D. G., Pieroni, M., Ricciardone, A., & Simakachorn, P. (2024). Cosmological Background Interpretation of Pulsar Timing Array Data. Phys. Rev. Lett., 132(17), 171002–9pp.
Abstract: We discuss the interpretation of the detected signal by pulsar timing array (PTA) observations as a gravitational wave background of cosmological origin. We combine NANOGrav 15-years and EPTADR2new datasets and confront them against backgrounds from supermassive black hole binaries (SMBHBs), and cosmological signals from inflation, cosmic (super)strings, first-order phase transitions, Gaussian and non-Gaussian large scalar fluctuations, and audible axions. We find that scalar-induced, and to a lesser extent audible axion and cosmic superstring signals, provide a better fit than SMBHBs. These results depend, however, on modeling assumptions, so further data and analysis are needed to reach robust conclusions. Independently of the signal origin, the data strongly constrain the parameter space of cosmological signals, for example, setting an upper bound on primordial non-Gaussianity at PTA scales as jfraj less than or similar to 2.34 at 95% C.L.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., Cabrera Urban, S., et al. (2023). Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in Pb plus Pb Collisions at √sNN=5.02 TeV with the ATLAS Detector. Phys. Rev. Lett., 131(17), 172301–22pp.
Abstract: This letter presents a measurement of the nuclear modification factor of large-radius jets in root s(NN) = 5.02 TeV Pb thorn Pb collisions by the ATLAS experiment. The measurement is performed using 1.72 nb(-1) and 257 pb(-1) of Pb thorn Pb and pp data, respectively. The large-radius jets are reconstructed with the anti-kt algorithm using a radius parameter of R = 1.0, by reclustering anti-k(t) R = 0.2 jets, and are measured over the transverse momentum (p(T)) kinematic range of 158 < p(T) < 1000 GeV and absolute pseudorapidity |y| < 2.0. The large-radius jet constituents are further reclustered using the k(t) algorithm in order to obtain the splitting parameters, root d(12) and Delta R-12, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, R-AA, obtained by comparing the Pb thorn Pb jet yields to those in pp collisions, is measured as a function of jet transverse momentum (p(T)) and root d(12) or Delta R-12. A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of R-AA for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression.
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Bodenstein, S., Bordes, J., Dominguez, C. A., Peñarrocha, J., & Schilcher, K. (2010). Charm-quark mass from weighted finite energy QCD sum rules. Phys. Rev. D, 82(11), 114013–5pp.
Abstract: The running charm-quark mass in the scheme is determined from weighted finite energy QCD sum rules involving the vector current correlator. Only the short distance expansion of this correlator is used, together with integration kernels (weights) involving positive powers of s, the squared energy. The optimal kernels are found to be a simple pinched kernel and polynomials of the Legendre type. The former kernel reduces potential duality violations near the real axis in the complex s plane, and the latter allows us to extend the analysis to energy regions beyond the end point of the data. These kernels, together with the high energy expansion of the correlator, weigh the experimental and theoretical information differently from e. g. inverse moments finite energy sum rules. Current, state of the art results for the vector correlator up to four-loop order in perturbative QCD are used in the finite energy sum rules, together with the latest experimental data. The integration in the complex s plane is performed using three different methods: fixed order perturbation theory, contour improved perturbation theory, and a fixed renormalization scale mu. The final result is (m) over bar (c)(3 GeV) = 1008 +/- 26 MeV, in a wide region of stability against changes in the integration radius s(0) in the complex s plane.
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Bertone, G., Cerdeño, D. G., Fornasa, M., Ruiz de Austri, R., & Trotta, R. (2010). Identification of dark matter particles with LHC and direct detection data. Phys. Rev. D, 82(5), 055008–7pp.
Abstract: Dark matter (DM) is currently searched for with a variety of detection strategies. Accelerator searches are particularly promising, but even if weakly interacting massive particles are found at the Large Hadron Collider (LHC), it will be difficult to prove that they constitute the bulk of the DM in the Universe Omega(DM). We show that a significantly better reconstruction of the DM properties can be obtained with a combined analysis of LHC and direct detection data, by making a simple Ansatz on the weakly interacting massive particles local density rho(0)((chi) over bar1), i.e., by assuming that the local density scales with the cosmological relic abundance, (rho(0)((chi) over bar1)/rho(DM)) = (Omega(0)((chi) over bar1)/Omega(DM)). We demonstrate this method in an explicit example in the context of a 24-parameter supersymmetric model, with a neutralino lightest supersymmetric particle in the stau coannihilation region. Our results show that future ton-scale direct detection experiments will allow to break degeneracies in the supersymmetric parameter space and achieve a significantly better reconstruction of the neutralino composition and its relic density than with LHC data alone.
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Fileviez Perez, P., Iminniyaz, H., Rodrigo, G., & Spinner, S. (2010). Gauge mediated supersymmetry breaking via seesaw mechanisms. Phys. Rev. D, 81(9), 095013–12pp.
Abstract: We present a simple scenario for gauge mediated supersymmetry breaking (GMSB) where the messengers are also the fields that generate neutrino masses. We show that the simplest such scenario corresponds to the case where neutrino masses are generated through the type I and type III seesaw mechanisms. The entire supersymmetric spectrum and Higgs masses are calculable from only four input parameters. Since the electroweak symmetry is broken through a doubly radiative mechanism, meaning a nearly zero B term at the messenger scale which runs down to acceptable values, one obtains quite a constrained spectrum for the supersymmetric particles whose properties we describe. We refer to this mechanism as "nu GMSB.''
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