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Driencourt-Mangin, F., Rodrigo, G., Sborlini, G. F. R., & Torres Bobadilla, W. J. (2022). Interplay between the loop-tree duality and helicity amplitudes. Phys. Rev. D, 105(1), 016012–13pp.
Abstract: The spinor-helicity formalism has proven to be very efficient in the calculation of scattering amplitudes in quantum field theory, while the loop-tree duality (LTD) representation of multiloop integrals exhibits appealing and interesting advantages with respect to other approaches. In view of the most recent developments in LTD, we exploit the synergies with the spinor-helicity formalism to analyze illustrative one- and two-loop scattering processes. We focus our discussion on the local UV renormalization of IR and UV finite helicity amplitudes and present a fully automated numerical implementation that provides efficient expressions, which are integrable directly in four space-time dimensions.
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Centelles Chulia, S., Rodejohann, W., & Saldana-Salazar, U. J. (2020). Two-Higgs-doublet models with a flavored Z(2) symmetry. Phys. Rev. D, 101(3), 035013–12pp.
Abstract: Two-Higgs-doublet models usually consider an ad-hoc Z(2) discrete symmetry to avoid flavor changing neutral currents. We consider a new class of two-Higgs-doublet models where Z(2) is enlarged to the symmetry group F(sic)Z(2), i.e., an inner semidirect product of a discrete symmetry group F and Z(2). In such a scenario, the symmetry constrains the Yukawa interactions but goes unnoticed by the scalar sector. In the most minimal scenario, Z(3)(sic)Z(2) = D-3, flavor changing neutral currents mediated by scalars are absent at tree and one-loop level, while at the same time predictions to quark and lepton mixing are obtained, namely a trivial Cabibbo-Kobayashi-Maskawa matrix and a Pontecorvo-Maki-Nakagawa-Sakata matrix (upon introduction of three heavy right-handed neutrinos) containing maximal atmospheric mixing. Small extensions allow to fully reproduce mixing parameters, including cobimaximal mixing in the lepton sector (maximal atmospheric mixing and a maximal charge-parity violating phase).
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., et al. (2020). Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector. Phys. Rev. D, 101(3), 032009–30pp.
Abstract: A search for the direct production of the supersymmetric partners of tau-leptons (staus) in final states with two hadronically decaying tau-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of 139 fb(-1), recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one tau-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Determination of quantum numbers for several excited charmed mesons observed in B- -> D*(+)pi(-) pi(-) decays. Phys. Rev. D, 101(3), 032005–24pp.
Abstract: A four-body amplitude analysis of the B- -> D*(+)pi(-) pi(-) decay is performed, where fractions and relative phases of the various resonances contributing to the decay are measured. Several quasi-model-independent analyses are performed aimed at searching for the presence of new states and establishing the quantum numbers of previously observed charmed meson resonances. In particular the resonance parameters and quantum numbers are determined for the D-1 (2420), D-1 (2430), D-0 (2550), D-1* (2600), D-2 (2740) and D-3*(2750) states. The mixing between the D-1 (2420) and D-1 (2430) resonances is studied and the mixing parameters are measured. The dataset corresponds to an integrated luminosity of 4.7 fb(-1), collected in proton-proton collisions at center-of-mass energies of 7, 8 and 13 TeV with the LHCb detector.
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McDermott, S. D., & Witte, S. J. (2020). Cosmological evolution of light dark photon dark matter. Phys. Rev. D, 101(6), 063030–14pp.
Abstract: Light dark photons are subject to various plasma effects, such as Debye screening and resonant oscillations, which can lead to a more complex cosmological evolution than is experienced by conventional cold dark matter candidates. Maintaining a consistent history of dark photon dark matter requires ensuring that the superthennal abundance present in the early Universe (i) does not deviate significantly after the formation of the cosmic microwave background (CMB), and (ii) does not excessively leak into the Standard Model plasma after big band nucleosynthesis (BBN). We point out that the role of nonresonant absorption, which has previously been neglected in cosmological studies of this dark matter candidate, produces strong constraints on dark photon dark matter with mass as low as 10(-22) eV. Furthermore, we show that resonant conversion of dark photons after recombination can produce excessive heating of the intergalactic medium (IGM) which is capable of prematurely reionizing hydrogen and helium, leaving a distinct imprint on both the Ly-a forest and the integrated optical depth of the CMB. Our constraints surpass existing cosmological bounds by more than 5 orders of magnitude across a wide range of dark photon masses.
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Nebot, M. (2020). Bounded masses in two Higgs doublets models, spontaneous CP violation and Z(2) symmetry. Phys. Rev. D, 102(11), 115002–16pp.
Abstract: In two Higgs doublet models (2HDMs) shaped by some unbroken symmetry, imposing perturbativity requirements on the quartic couplings can imply that the allowed masses of all the fundamental scalars are bounded from above. This important property is analyzed in detail for the only two realistic 2HDMs with an exact symmetry, the case with Z(2) symmetry and the case with CP symmetry. It is also noticeable that one exception arises in each case: when the vacuum is assumed to respect the imposed symmetry, a decoupling regime can nevertheless appear without violating perturbativity requirements. In both models with an exact symmetry and no decoupling regime, soft symmetry breaking terms can however lead to a decoupling regime: the possibility that this regime might be unnatural, since it requires some fine-tuning, is also analyzed.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). (U)pdated measurement of decay-time-dependent CP asymmetries in D-0 -> K+ K- and D-0 -> pi(+)pi(-) decays. Phys. Rev. D, 101(1), 012005–12pp.
Abstract: A search for decay-time-dependent charge-parity (CP) asymmetry in D-0 -> K+ K- and D-0 -> pi(+)pi(-) eff decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 5.4 fb(-1). The D-0 mesons are required to originate from semileptonic decays of b hadrons, such that the charge of the muon identifies the flavor of the neutral D meson at production. The asymmetries in the effective decay widths of D-0 and (D) over bar (0) mesons are determined to be A(Gamma)(K+ K-) = (-4.3 +/- 3.6 +/- 0.5) x 10(-4) and A(Gamma) (K+ K- ) = (2.2 +/- 7.0 +/- 0.8) x 10(-4), where the uncertainties are statistical and systematic, respectively. The results are consistent with CP symmetry and, when combined with previous LHCb results, yield A(Gamma) (K+ K-) = (-4.4 +/- 2.3 +/- 0.6) x 10(-4) and A(Gamma) (pi(+)pi(-))= (2.5 +/- 4.3 +/- 0.7) x 10(-4).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2019). Measurement of the B-c(-) meson production fraction and asymmetry in 7 and 13 TeV pp collisions. Phys. Rev. D, 100(11), 112006–17pp.
Abstract: The production fraction of the B-c(-) meson with respect to the sum of B- and (B) over bar (0) mesons is measured in both 7 and 13 TeV center-of-mass (c.m.) energy pp collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mine, does not change with energy, but shows a transverse momentum dependence. The B-c(-) – B-c(+) production asymmetry is also measured and is consistent with zero within the determined statistical and systematic uncertainties of a few percent.
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Coppola, M., Gomez Dumm, D., Noguera, S., & Scoccola, N. N. (2020). Weak decays of magnetized charged pions in the symmetric gauge. Phys. Rev. D, 101(3), 034003–13pp.
Abstract: We consider the decay pi(-) -> l (nu) over bar (l) (l = e(-) , mu(-)) in the presence of an arbitrary large uniform magnetic field, using the symmetric gauge. The consequences of the axial symmetry of the problem and the issue of angular momentum conservation arc discussed in detail. In particular, we analyze the projection of both the canonical and the mechanical total angular momenta along the direction of the magnetic field. It is found that while the former is conserved in the symmetric gauge, the latter is not conserved in both the symmetric and Landau gauges. We derive an expression for the integrated pi(-) -> l (nu) over bar (l) width that coincides exactly with the one we previously found using the Landau gauge, providing an explicit test of the gauge independence of that result. Such an expression implies that for nonzero magnetic fields the decay width does not vanish in the limit in which the outgoing charged leptons can be considered as massless, i.e., it does not exhibit the helicity suppression found in the case of no external field.
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Di Valentino, E., Melchiorri, A., Mena, O., & Vagnozzi, S. (2020). Nonminimal dark sector physics and cosmological tensions. Phys. Rev. D, 101(6), 063502–20pp.
Abstract: We explore whether nonstandard dark sector physics might be required to solve the existing cosmological tensions. The properties we consider in combination are (a) an interaction between the dark matter and dark energy components and (b) a dark energy equation of state w different from that of the canonical cosmological constant w = -1. In principle, these two parameters are independent. In practice, to avoid early-time, superhorizon instabilities, their allowed parameter spaces are correlated. Moreover, a clear degeneracy exists between these two parameters in the case of cosmic microwave background (CMB) data. We analyze three classes of extended interacting dark energy models in light of the 2019 Planck CMB results and Cepheid-calibrated local distance ladder H-0 measurements of Riess et al. (R19), as well as recent baryon acoustic oscillation (BAO) and type Ia supernovae (SNeIa) distance data. We find that in quintessence coupled dark energy models, where w > -1, the evidence for a nonzero coupling between the two dark sectors can surpass the 5 sigma significance. Moreover, for both Planck + BAO or Planck + SNeIa, we find a preference for w > -1 at about three standard deviations. Quintessence models are, therefore, in excellent agreement with current data when an interaction is considered. On the other hand, in phantom coupled dark energy models, there is no such preference for a nonzero dark sector coupling. All the models we consider significantly raise the value of the Hubble constant, easing the H-0 tension. In the interacting scenario, the disagreement between Planck thorn BAO and R19 is considerably reduced from 4.3 sigma in the case of the Lambda cold dark matter (Lambda CDM) model to about 2.5 sigma. The addition of low-redshift BAO and SNeIa measurements leaves, therefore, some residual tension with R19 but at a level that could be justified by a statistical fluctuation. Bayesian evidence considerations mildly disfavor both the coupled quintessence and phantom models, while mildly favoring a coupled vacuum scenario, even when late-time datasets are considered. We conclude that nonminimal dark energy cosmologies, such as coupled quintessence, phantom, or vacuum models, are still an interesting route toward softening existing cosmological tensions, even when low-redshift datasets and Bayesian evidence considerations are taken into account.
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