Search results for "53"
showing 10 items of 2908 documents
Signature of the presence of a third body orbiting around XB 1916-053
2015
The ultra-compact dipping source \object{XB 1916-053} has an orbital period of close to 50 min and a companion star with a very low mass (less than 0.1 M$_{\odot}$). The orbital period derivative of the source was estimated to be $1.5(3) \times 10^{-11}$ s/s through analysing the delays associated with the dip arrival times obtained from observations spanning 25 years, from 1978 to 2002. The known orbital period derivative is extremely large and can be explained by invoking an extreme, non-conservative mass transfer rate that is not easily justifiable. We extended the analysed data from 1978 to 2014, by spanning 37 years, to verify whether a larger sample of data can be fitted with a quadra…
Measurement of the cosmic ray energy spectrum with IceTop-73
2013
Physical review / D 88(4), 042004 (2013). doi:10.1103/PhysRevD.88.042004
Modified majoron model for cosmological anomalies
2020
The vacuum expectation value $v_s$ of a Higgs triplet field $\Delta$ carrying two units of lepton number $L$ induces neutrino masses $\propto v_s$. The neutral component of $\Delta$ gives rise to two Higgs particles, a pseudoscalar $A$ and a scalar $S$. The most general renormalizable Higgs potential $V$ for $\Delta $ and the Standard-Model Higgs doublet $\Phi$ does not permit the possibility that the mass of either $A$ or $S$ is small, of order $v_s$, while the other mass is heavy enough to forbid the decay $Z\to A S$ to comply with LEP 1 data. We present a model with additional dimension-6 terms in $V$, in which this feature is absent and either $A$ or $S$ can be chosen light. Subsequentl…
Search for invisible decays of the Λ baryon
2022
Physical review / D 105(7), L071101 (2022). doi:10.1103/PhysRevD.105.L071101
Aspects of chiral symmetry in QCD at T = 128 MeV
2023
We investigate several aspects of chiral symmetry in QCD at a temperature of $T = 128\,\text{MeV}$. The study is based on a $24\times 96^3$ lattice-QCD ensemble with O($a$)-improved Wilson quarks and physical up, down and strange quark masses. The pion quasiparticle turns out to be significantly lighter than the zero-temperature pion mass, even though the corresponding static correlation length is shorter. We perform a quantitative comparison of our findings to predictions of chiral perturbation theory. Among several order parameters for chiral symmetry restoration, we compute the difference of the vector- and axial-vector time-dependent correlators and find it to be reduced by a factor $\s…
Fully nonperturbative charm-quark tuning using machine learning
2022
We present a relativistic heavy-quark action tuning for the charm sector on ensembles generated by the CLS consortium. We tune a particular 5-parameter action in an entirely non-perturbative and -- up to the chosen experimental input -- model-independent way using machine learning and the continuum experimental charmonium ground-state masses with various quantum numbers. In the end we are reasonably successful; obtaining a set of simulation parameters that we then verify produces the expected spectrum. In the future, we will use this action for finite-volume calculations of hadron-hadron scattering.
Spectral signatures of axionlike dark matter
2022
We derive spectral line shapes of the expected signal for a haloscope experiment searching for axionlike dark matter. The knowledge of these line shapes is needed to optimize an experimental design and data analysis procedure. We extend the previously known results for the axion-photon and axion-gluon couplings to the case of gradient (axion-fermion) coupling. A unique feature of the gradient interaction is its dependence not only on magnitudes but also on directions of velocities of galactic halo particles, which leads to the directional sensitivity of the corresponding haloscope. We also discuss the daily and annual modulations of the gradient signal caused by the Earth's rotational and o…
Isovector Axial Form Factor of the Nucleon from Lattice QCD
2022
The isovector axial form factor of the nucleon plays a key role in interpreting data from long-baseline neutrino oscillation experiments. We present a lattice QCD calculation of this form factor, introducing a new method to directly extract its z-expansion from lattice correlators. Our final parameterization of the form factor, which extends up to spacelike virtualities of 0.7 GeV^2 with fully quantified uncertainties, agrees with previous lattice calculations but is significantly less steep than neutrino-deuterium scattering data suggests.
Pseudovector and pseudoscalar spin-dependent interactions in atoms
2019
Hitherto unknown elementary particles can be searched for with atomic spectroscopy. We conduct such a search using a potential that results from the longitudinal polarization of a pseudovector particle. We show that such a potential, inversely proportional to the boson's mass squared, $V \propto 1/M^2$, can stay finite at $M \to 0$ if the theory is renormalizable. We also look for a pseudoscalar boson, which induces a contact spin-dependent potential that does not contribute to new forces searched for in experiments with macroscopic objects, but may be seen in atomic spectroscopy. We extract limits on the interaction constants of these potentials from the experimental spectra of antiprotoni…
The cosmic QCD transition for large lepton flavour asymmetries
2022
We study the impact of large lepton flavour asymmetries on the cosmic QCD transition. Scenarios of unequal lepton flavour asymmetries are observationally almost unconstrained and therefore open up a whole new parameter space for the cosmic QCD transition. We find that for large asymmetries the formation of a Bose-Einstein condensate of pions can occur and identify the corresponding parameter space. In the vicinity of the QCD transition scale, we express the pressure in terms of a Taylor expansion with respect to the complete set of chemical potentials. The Taylor coefficients rely on input from lattice QCD calculations from the literature. The domain of applicability of this method is discu…