Electroweak Origin Research Articles

Improving methods and predictions at high-energy e+e− colliders within collinear factorisation

We illustrate how electron Parton Distribution Functions (PDFs) with next-to-leading collinear logarithmic accuracy must be employed in the context of perturbative predictions for high-energy e+e−-collision processes. In particular, we discuss how the renormalisation group equation evolution of such PDFs is affected by the presence of multiple fermion families and their respective mass thresholds, and by the dependences on the choices of the factorisation and renormalisation schemes. We study the impact of the uncertainties associated with the PDFs on physical cross sections, in order to arrive at realistic precision estimates for observables computed with collinear-factorisation formulae. We do so by presenting results for the production of a heavy neutral object as well as for toverline{t} and W+W− pairs, including next-to-leading-order effects of electroweak origin.

Full NLO corrections to 3-jet production and mathbf {R_{32}} at the LHC

We present the evaluation of the complete set of NLO corrections to three-jet production at the LHC. To this end we consider all contributions of mathcal{{O}}(alpha _s^nalpha ^m) with n+m=3 and n+m=4. This includes in particular also subleading Born contributions of electroweak origin, as well as electroweak virtual and QED real-radiative corrections. As an application we present results for the three- over two-jet ratio R_{32}. While the impact of non-QCD corrections on the total cross section is rather small, they can exceed -10% for high jet transverse momenta. The R_{32} observable turns out to be very stable against electroweak corrections, receiving absolute corrections below 5% even in the high-p_T region.

An automated subtraction of NLO EW infrared divergences

In this paper a generalisation of the Catani–Seymour dipole subtraction method to next-to-leading order electroweak calculations is presented. All singularities due to photon and gluon radiation off both massless and massive partons in the presence of both massless and massive spectators are accounted for. Particular attention is paid to the simultaneous subtraction of singularities of both QCD and electroweak origin which are present in the next-to-leading order corrections to processes with more than one perturbative order contributing at Born level. Similarly, embedding non-dipole-like photon splittings in the dipole subtraction scheme discussed. The implementation of the formulated subtraction scheme in the framework of the Sherpa Monte-Carlo event generator, including the restriction of the dipole phase space through the alpha -parameters and expanding its existing subtraction for NLO QCD calculations, is detailed and numerous internal consistency checks validating the obtained results are presented.

Gravity-mediated (or composite) dark matter

Dark matter could have an electroweak origin, yet communicate with the visible sector exclusively through gravitational interactions. In a set-up addressing the hierarchy problem, we propose a new dark matter scenario where gravitational mediators, arising from the compactification of extra-dimensions, are responsible for dark matter interactions and its relic abundance in the Universe. We write an explicit example of this mechanism in warped extra-dimensions and work out its constraints. We also develop a dual picture of the model, based on a four-dimensional scenario with partial compositeness. We show that Gravity-mediated Dark Matter is equivalent to a mechanism of generating viable dark matter scenarios in a strongly-coupled, near-conformal theory, such as in composite Higgs models.

Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life

The origin of homochirality in life remains a mystery that some believe is essential for life, and which may result from chiral symmetry breaking interactions with galactic organic material.

Erratum to: Origins of Life and Evolution of Biospheres

In the previous issue, the three papers by MacDermott et al. appeared in incorrect order. The correct sequence should be: Evaluation of Coupled Perturbed and Density Functional Methods of Computing the ParityViolating Energy Difference between Enantiomers Electroweak Parity-Violating Energy Shifts of Amino Acids: The “Conformation Problem” Parity-Violating Energy Shifts of Murchison L-Amino Acids are Consistent with an Electroweak Origin of Meteorite L-Enantiomeric Excesses Orig Life Evol Biosph (2009) 39:599 DOI 10.1007/s11084-009-9176-3

Parity-violating energy shifts of Murchison L-amino acids are consistent with an electroweak origin of meteorite L-enantiomeric excesses.

In 1996, four alpha-methyl amino acids in the Murchison meteorite--L-isovaline, L-alpha-methylnorvaline, L-alpha-methyl-allo-isoleucine and L-alpha-methyl-isoleucine--were found to show significant enantiomeric excesses of the L form, ranging from 2% to 9%. Their deuterium to hydrogen isotope ratios suggest they formed in the pre-solar interstellar gas cloud rather than during a later aqueous processing phase on the asteroid parent body. In this paper we apply the techniques of the preceding two papers to compute the parity-violating energy shifts of these amino acids. We find that, in the gas phase, the PVESs of the neutral L forms of all four Murchison alpha-methyl amino acids are decisively negative, and there is even some correlation between the magnitudes of the L-excesses and the magnitudes of the PVESs--all of which is at least consistent with an electroweak origin of the Murchison enantiomeric excesses.

PLASMA INDUCED FERMION SPIN–FLIP CONVERSION fL → fR + γ

The fermion spin–flip conversion fL → fR + γ is considered, caused by the difference of the additional energies of the electroweak origin, acquired by left- and right-handed fermions (neutrino, electron) in medium. An accurate analysis of the fermion and photon dispersion in medium is performed. It is shown that the threshold arises in the process, caused by the photon (plasmon) effective mass. This threshold leaves no room for the so-called "spin light of neutrino" and "spin light of electron" in the real astrophysical situations.

On the radiative corrections to the pseudo-scalar Higgs boson mass

We reexamine the one-loop corrections to the mass of the pseudo-scalar Higgs boson, using the effective potential. In the absence of the chargino and neutralino contributions its mass exhibits a large scale dependence in the large M 1/2 regime, especially for values of tan β>20. Thus, although of electroweak origin, the heaviness of the M 1/2, in conjunction with the largeness of tan β, makes these corrections very important for establishing a scale independent result and an unambiguous determination of the pseudo-scalar mass in this region of the parameter space.

Electroweak origin of cosmological magnetic fields

Magnetic fields may have been generated in the electroweak phase transition through spontaneous symmetry breaking or through the subsequent dynamical evolution of semiclassical field configurations. Here I demonstrate explicitly how magnetic fields emerge spontaneously in the phase transition also when no gradients of the Higgs field are present. Using a simple model, I show that no magnetic fields are generated, at least initially, from classical two-bubble collisions in a first-order phase transition. An improved gauge-invariant definition of the electromagnetic field is advocated which is more appropriate in the sense that it never allows electrically neutral fields to serve as sources for the electromagnetic field. In particular, semiclassical configurations of the $Z$ field alone do not generate magnetic fields. The possible generation of magnetic fields in the decay of unstable $Z$ strings is discussed.

Computational studies of the electroweak origin of biomolecular handedness in natural sugars

The violation of parity by the weak interactions ensures that enantiomeric chiral molecules have inequivalent energies. These parity violating energy differences have been calculated, usingab initiomethods, for the biologically important sugars deoxyribose, ribose, arabinose, xylose and lyxose. It is found that in each case the choice of which enantiomer is of lower energy is dependent on the molecular conformation adopted, particularly the type of furanose ring pucker. In general the D-enantiomers are favoured for molecules having a C2-endo pucker, whereas the L-series are preferred for C3-endo puckers. The significance of these energy differences for the transition from a prebiotic racemic geochemistry to a homochiral biochemistry in terrestrial evolution is discussed.

The electroweak origin of biomolecular handedness

The parity-violating weak neutral current perturbation of the ground-state electronic energy has been calculated by ab initio methods for glycine over a range of chiral conformations, for L-alanine, L-α-aminopropionitrile, and for the peptide residue of polypeptides in the α-helix and the β-sheet conformation. It is found that L-alanine in its preferred conformation in aqueous solution and the L-peptides in the α-helix and the β-sheet conformation, have a lower ground-state energy than the corresponding D-enantiomers, because of the electroweak interaction. The enantiomer energy difference is small, of the order of 10 -14 J mol -1 , corresponding to an enantiomeric excess of 10 6 molecules of L-alanine or the L-peptide in one mole of the corresponding racemic mixture in thermodynamic equilibrium at ambient temperature. The significance of the energy difference between enantiomers arising from the electroweak interaction for the transition from racemic geochemistry to homochiral biochemistry in terrestrial evolution is discussed.