Gessner, M., & Smerzi, A. (2023). Hierarchies of Frequentist Bounds for Quantum Metrology: From Cramer-Rao to Barankin. Phys. Rev. Lett., 130(26), 260801–6pp.
Abstract: We derive lower bounds on the variance of estimators in quantum metrology by choosing test observables that define constraints on the unbiasedness of the estimator. The quantum bounds are obtained by analytical optimization over all possible quantum measurements and estimators that satisfy the given constraints. We obtain hierarchies of increasingly tight bounds that include the quantum Cramer-Rao bound at the lowest order. In the opposite limit, the quantum Barankin bound is the variance of the locally best unbiased estimator in quantum metrology. Our results reveal generalizations of the quantum Fisher information that are able to avoid regularity conditions and identify threshold behavior in quantum measurements with mixed states, caused by finite data.
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Biggio, C., Fernandez-Martinez, E., Filaci, M., Hernandez-Garcia, J., & Lopez-Pavon, J. (2020). Global bounds on the Type-III Seesaw. J. High Energy Phys., 05(5), 022–33pp.
Abstract: We derive general bounds on the Type-III Seesaw parameters from a global fit to flavor and electroweak precision data. We explore and compare three Type-III Seesaw realizations: a general scenario, where an arbitrary number of heavy triplets is integrated out without any further assumption, and the more constrained cases in which only 3 or 2 (minimal scenario) additional heavy states are included. The latter assumption implies rather non-trivial correlations in the Yukawa flavor structure of the model so as to reproduce the neutrino masses and mixings as measured in neutrino oscillations experiments and thus qualitative differences can be found with the more general scenario. In particular, we find that, while the bounds on most elements of the dimension 6 operator coefficients are of order 10(-4) for the general and 3-triplet cases, the 2-triplet scenario is more strongly constrained with bounds between 10(-5) and 10(-7) for the different flavours. We also discuss how these correlations affect the present CMS constraints on the Type-III Seesaw in the minimal 2-triplet scenario.
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Davesne, D., Holt, J. W., Navarro, J., & Pastore, A. (2023). Landau sum rules with noncentral quasiparticle interactions. Phys. Rev. C, 108(3), 034003–7pp.
Abstract: We derive explicit expressions for the Landau sum rules for the case of the most general spin-dependent quasiparticle interaction including all possible tensor interactions. For pure neutron matter, we investigate the convergence of the sum rules at different orders of approximation. Employing modern nuclear Hamiltonians based on chiral effective field theory, we find that the inclusion of noncentral interactions improves the convergence of the sum rules only for low densities (n <= 0.1 fm-3). Around nuclear matter saturation density, we find that even ostensibly perturbative nuclear interactions violate the sum rules considerably. By artificially weakening the strength of the nuclear Hamiltonian, the convergence can be improved.
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Caputo, A., Sberna, L., Frias, M., Blas, D., Pani, P., Shao, L. J., et al. (2019). Constraints on millicharged dark matter and axionlike particles from timing of radio waves. Phys. Rev. D, 100(6), 063515–7pp.
Abstract: We derive constraints on millicharged dark matter and axionlike particles using pulsar timing and fast radio burst observations. For dark matter particles of charge epsilon e, the constraint from time of arrival (TOA) of waves is epsilon/m(milli) less than or similar to 10(-8) eV(-1), for masses m(milli) greater than or similar to 10(-6) eV. For axionlike particles, the polarization of the signals from pulsars yields a bound in the axial coupling g/ m(a) less than or similar to 10(-13) Gev(-1)/(10(-22) eV),for m(a) less than or similar to 10(-19) eV. Both bounds scale as (rho/rho(dm))(1/2 )for fractions of the total dark matter energy density rho(dm). We make a precise study of these bounds using TOA from several pulsars, FRB 121102, and polarization measurements of PSR J0437 – 4715. Our results rule out a new region of the parameter space for these dark matter models.
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Renner, J., Cervera-Villanueva, A., Hernando, J. A., Izmaylov, A., Monrabal, F., Muñoz, J., et al. (2015). Improved background rejection in neutrinoless double beta decay experiments using a magnetic field in a high pressure xenon TPC. J. Instrum., 10, P12020–19pp.
Abstract: We demonstrate that the application of an external magnetic field could lead to an improved background rejection in neutrinoless double-beta (0 nu beta beta) decay experiments using a high-pressure xenon (HPXe) TPC. HPXe chambers are capable of imaging electron tracks, a feature that enhances the separation between signal events (the two electrons emitted in the 0 nu beta beta decay of Xe-136) and background events, arising chiefly from single electrons of kinetic energy compatible with the end-point of the 0 nu beta beta decay (Q(beta beta)). Applying an external magnetic field of sufficiently high intensity (in the range of 0.5-1 Tesla for operating pressures in the range of 5-15 atmospheres) causes the electrons to produce helical tracks. Assuming the tracks can be properly reconstructed, the sign of the curvature can be determined at several points along these tracks, and such information can be used to separate signal (0 nu beta beta) events containing two electrons producing a track with two different directions of curvature from background (single-electron) events producing a track that should spiral in a single direction. Due to electron multiple scattering, this strategy is not perfectly efficient on an event-by-event basis, but a statistical estimator can be constructed which can be used to reject background events by one order of magnitude at a moderate cost (about 30%) in signal efficiency. Combining this estimator with the excellent energy resolution and topological signature identification characteristic of the HPXe TPC, it is possible to reach a background rate of less than one count per ton-year of exposure. Such a low background rate is an essential feature of the next generation of 0 nu beta beta experiments, aiming to fully explore the inverse hierarchy of neutrino masses.
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Centelles Chulia, S., Cepedello, R., Peinado, E., & Srivastava, R. (2020). Scotogenic dark symmetry as a residual subgroup of Standard Model symmetries. Chin. Phys. C, 44(8), 083110–7pp.
Abstract: We demonstrate that a scotogenic dark symmetry can be obtained as a residual subgroup of the global U(1)(B-L) symmetry already present in the Standard Model. In addition, we propose a general framework in which the U(1)(B-L) symmetry is spontaneously broken into an even Z(2n) subgroup, setting the general conditions for neutrinos to be Majorana and for dark matter stability to exist in terms of the residual Z(2n). As an example, under this general framework, we build a class of simple models where, in a scotogenic manner, the dark matter candidate is the lightest particle running inside the mass loop of a neutrino. The global U(1)(B-L) symmetry in our framework, being anomaly free, can also be gauged in a straightforward manner leading to a richer phenomenology.
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Tang, C., Gao, F., & Liu, Y. X. (2019). Practical scheme from QCD to phenomena via Dyson-Schwinger equations. Phys. Rev. D, 100(5), 056001–16pp.
Abstract: We deliver a scheme to compute the quark propagator and the quark-gluon interaction vertex through the coupled Dyson-Schwinger equations (DSEs) of QCD. We take the three-gluon vertex into account in our calculations, and implement the gluon propagator and the running coupling function fitted by the solutions of their respective DSEs. We obtain the momentum and current mass dependence of the quark propagator and the quark-gluon vertex, and the chiral quark condensate that agrees with previous results excellently. We also compute the quark-photon vertex within this scheme and give the anomalous chromo- and electromagnetic moment of the quark. The obtained results are excellently consistent with previous ones. These applications manifest that the scheme is realistic and then practical for explaining the QCD-related phenomena.
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Delhom, A. (2020). Minimal coupling in presence of non-metricity and torsion. Eur. Phys. J. C, 80(8), 728–17pp.
Abstract: We deal with the question of what it means to define a minimal coupling prescription in presence of torsion and/or non-metricity, carefully explaining while the naive substitution partial derivative -> del introduces extra couplings between the matter fields and the connection that can be regarded as non-minimal in presence of torsion and/or non-metricity. We will also investigate whether minimal coupling prescriptions at the level of the action (MCPL) or at the level of field equations (MCPF) lead to different dynamics. To that end, we will first write the Euler-Lagrange equations for matter fields in terms of the covariant derivatives of a general non-Riemannian space, and derivate the form of the associated Noether currents and charges. Then we will see that if the minimal coupling prescriptions is applied as we discuss, for spin 0 and 1 fields the results of MCPL and MCPF are equivalent, while for spin 1/2 fields there is a difference if one applies the MCPF or the MCPL, since the former leads to charge violation.
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Bigaran, I., Felkl, T., Hagedorn, C., & Schmidt, M. A. (2023). Flavor anomalies meet flavor symmetry. Phys. Rev. D, 108(7), 075014–77pp.
Abstract: We construct an extension of the Standard Model with a scalar leptoquark Q iota similar to (3,1, – 13) and the discrete flavor symmetry Gf _ D17 x Z17 to explain anomalies observed in charged-current semileptonic B meson decays and in the muon anomalous magnetic moment, together with the charged fermion masses and quark mixing. The symmetry Zdiag 17 , contained in Gf, remains preserved by the leptoquark couplings, at leading order, and efficiently suppresses couplings of the leptoquark to the first generation of quarks and/or electrons, thus avoiding many stringent experimental bounds. The strongest constraints on the parameter space are imposed by the radiative charged lepton flavor violating decays a -mu y and μ-ey. A detailed analytical and numerical study demonstrates the feasibility to simultaneously explain the data on the lepton flavor universality ratios R(D) and R(D*) and the muon anomalous magnetic moment, while passing the experimental bounds from all other considered flavor observables.
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Barenboim, G., & Hill, C. T. (2021). Sterile neutrinos, black hole vacuum and holographic principle. Eur. Phys. J. C, 81(2), 150–9pp.
Abstract: We construct an effective field theory (EFT) model that describes matter field interactions with Schwarzschild mini-black-holes (SBH's), treated as a scalar field, B0(x). Fermion interactions with SBH's require a complex spurion field, theta ij, which we interpret as the EFT description of “holographic information,” which is correlated with the SBH as a composite system. We consider Hawking's virtual black hole vacuum (VBH) as a Higgs phase, B0=V. Integrating sterile neutrino loops, the information field theta ij is promoted to a dynamical field, necessarily developing a tachyonic instability and acquiring a VEV of order the Planck scale. For N sterile neutrinos this breaks the vacuum to SU(N)xU(1)/SO(N) with N degenerate Majorana masses, and <mml:mfrac>12</mml:mfrac>N(N+1) Nambu-Goldstone neutrino-Majorons. The model suggests many scalars fields, corresponding to all fermion bilinears, may exist bound nonperturbatively by gravity.
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