16 research outputs found
Gravitational Contributions to the Running Yang-Mills Coupling in Large Extra-Dimensional Brane Worlds
We study the question of a modification of the running gauge coupling of
Yang-Mills theories due to quantum gravitational effects in a compact large
extra dimensional brane world scenario with a low energy quantum gravity scale.
The ADD scenario is applied for a D=d+\delta dimensional space-time in which
gravitons freely propagate, whereas the non-abelian gauge fields are confined
to a d-dimensional brane. The extra dimensions are taken to be toroidal and the
transverse fluctuation modes (branons) of the brane are taken into account. On
this basis we have calculated the one-loop corrections due to virtual
Kaluza-Klein graviton and branon modes for the gluon two- and three-point
functions in an effective field theory treatment. Applying momentum cut-off
regularization we find that for a d=4 brane the leading gravitational
divergencies cancel irrespective of the number of extra dimensions \delta,
generalizing previous results in the absence of extra-dimensions. Hence, again
the Yang-Mills \beta-function receives no gravitational corrections at
one-loop. This is no longer true in a `universal' extra dimensional scenario
with a d>4 dimensional brane. Moreover, the subleading power-law gravitational
divergencies induce higher-dimensional counterterms, which we establish in our
scheme. Interestingly, for d=4 these gravitationally induced counterterms are
of the form recently considered in non-abelian Lee-Wick extensions of the
standard model -- now with a possible mass scale in the TeV range due to the
presence of large extra dimensions.Comment: Version to be published in JHEP; 16 pages, 3 figures; v3: references
update
Characterisation and optimisation of a sample preparation method for the detection and quantification of atmospherically relevant carbonyl compounds in aqueous medium
Carbonyl compounds are ubiquitous in the atmosphere and either emitted primarily from anthropogenic and biogenic sources or they are produced secondarily from the oxidation of volatile organic compounds. Despite a number of studies about the quantification of carbonyl compounds a comprehensive description of optimised methods is scarce for the quantification of atmospherically relevant carbonyl compounds. The method optimisation was conducted for seven atmospherically relevant carbonyl compounds including acrolein, benzaldehyde, glyoxal, methyl glyoxal, methacrolein, methyl vinyl ketone and 2,3-butanedione. O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was used as derivatisation reagent and the formed oximes were detected by gas chromatography/mass spectrometry (GC/MS). With the present method quantification can be carried out for each carbonyl compound originating from fog, cloud and rain or sampled from the gas- and particle phase in water. Detection limits between 0.01 and 0.17 μmol L−1 were found, depending on carbonyl compounds. Furthermore, best results were found for the derivatisation with a PFBHA concentration of 0.43 mg mL−1 for 24 h followed by a subsequent extraction with dichloromethane for 30 min at pH = 1. The optimised method was evaluated in the present study by the OH radical initiated oxidation of 3-methylbutanone in the aqueous phase. Methyl glyoxal and 2,3-butanedione were found to be oxidation products in the samples with a yield of 2% for methyl glyoxal and 14% for 2,3-butanedione after a reaction time of 5 h
Quantum gravitational contributions to quantum electrodynamics
Quantum electrodynamics describes the interactions of electrons and photons.
Electric charge (the gauge coupling constant) is energy dependent, and there is
a previous claim that charge is affected by gravity (described by general
relativity) with the implication that the charge is reduced at high energies.
But that claim has been very controversial with the situation inconclusive.
Here I report an analysis (free from earlier controversies) demonstrating that
that quantum gravity corrections to quantum electrodynamics have a quadratic
energy dependence that result in the reduction of the electric charge at high
energies, a result known as asymptotic freedom.Comment: To be published in Nature. 19 pages LaTeX, no figure
Fixed points and infrared completion of quantum gravity
The phase diagram of four-dimensional Einstein–Hilbert gravity is studied using Wilsonʼs renormalization group. Smooth trajectories connecting the ultraviolet fixed point at short distances with attractive infrared fixed points at long distances are derived from the non-perturbative graviton propagator. Implications for the asymptotic safety conjecture and further results are discussed
The other Higgses, at resonance, in the Lee-Wick extension of the Standard Model
Within the framework of the Lee Wick Standard Model (LWSM) we investigate
Higgs pair production , and top pair
production at the Large Hadron Collider (LHC), where the
neutral particles from the Higgs sector (, and )
appear as possible resonant intermediate states. We investigate the signal and we find that the LW Higgs,
depending on its mass-range, can be seen not long after the LHC upgrade in
2012. More precisely this happens when the new LW Higgs states are below the
top pair threshold. In the LW states, due to the wrong-sign
propagator and negative width, lead to a dip-peak structure instead of the
usual peak-dip structure which gives a characteristic signal especially for
low-lying LW Higgs states. We comment on the LWSM and the forward-backward
asymmetry in view of the measurement at the TeVatron. Furthermore, we present a
technique which reduces the hyperbolic diagonalization to standard
diagonalization methods. We clarify issues of spurious phases in the Yukawa
sector.Comment: 36 pages, 16 figures, 3 table
Gauge-invariant quantum gravitational corrections to correlation functions
A recent proposal for gauge-invariant observables in inflation [R. Brunetti et al., JHEP 1608 (2016) 032] is examined. We give a generalisation of their construction to general background spacetimes. In flat space, we calculate one-loop graviton corrections to a scalar two-point function in a general gauge for the graviton. We explicitely show how the gauge-dependent terms cancel between the usual self-energy contributions and the additional corrections inherent in these observables. The one-loop corrections have the expected functional form, contrary to another recently studied proposal for gauge-invariant observables [M. B. Fröb, Class. Quant. Grav. 35 (2018) 035005] where this is not the case. Furthermore, we determine the one-loop graviton corrections to the four-point coupling of the gauge-invariant scalar field, and the corresponding running of the coupling constant induced by graviton loops. Interestingly, the β function is negative for all values of the non-minimal coupling of the scalar field to curvature
A quantification method for heat-decomposable methylglyoxal oligomers and its application on 1,3,5-trimethylbenzene SOA
Methylglyoxal forms oligomeric compounds in the atmospheric aqueous particle
phase, which could establish a significant contribution to the formation of
aqueous secondary organic aerosol (aqSOA). Thus far, no suitable method for
the quantification of methylglyoxal oligomers is available despite the great
effort spent for structure elucidation. In the present study a simplified
method was developed to quantify heat-decomposable methylglyoxal oligomers
as a sum parameter. The method is based on the thermal decomposition of
oligomers into methylglyoxal monomers. Formed methylglyoxal monomers were
detected using PFBHA (o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine
hydrochloride) derivatisation and gas chromatography–mass spectrometry (GC/MS)
analysis. The method development was focused on the heating time
(varied between 15 and 48 h), pH during the heating process (pH = 1–7),
and heating temperature (50, 100 °C). The optimised values of these
method parameters are presented.
The developed method was applied to quantify heat-decomposable methylglyoxal
oligomers formed during the OH-radical oxidation of 1,3,5-trimethylbenzene (TMB)
in the Leipzig aerosol chamber (LEipziger AerosolKammer, LEAK). Oligomer formation was investigated as a function of seed particle acidity and relative humidity. A fraction of heat-decomposable methylglyoxal oligomers of up to 8 % in the produced organic particle mass was found, highlighting the importance of
those oligomers formed solely by methylglyoxal for SOA formation. Overall,
the present study provides a new and suitable method for quantification of
heat-decomposable methylglyoxal oligomers in the aqueous particle phase
A quantification method for heat-decomposable methylglyoxal oligomers and its application on 1,3,5-trimethylbenzene SOA
Methylglyoxal forms oligomeric compounds in the atmospheric aqueous particle
phase, which could establish a significant contribution to the formation of
aqueous secondary organic aerosol (aqSOA). Thus far, no suitable method for
the quantification of methylglyoxal oligomers is available despite the great
effort spent for structure elucidation. In the present study a simplified
method was developed to quantify heat-decomposable methylglyoxal oligomers
as a sum parameter. The method is based on the thermal decomposition of
oligomers into methylglyoxal monomers. Formed methylglyoxal monomers were
detected using PFBHA (o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine
hydrochloride) derivatisation and gas chromatography–mass spectrometry (GC/MS)
analysis. The method development was focused on the heating time
(varied between 15 and 48 h), pH during the heating process (pH = 1–7),
and heating temperature (50, 100 °C). The optimised values of these
method parameters are presented.
The developed method was applied to quantify heat-decomposable methylglyoxal
oligomers formed during the OH-radical oxidation of 1,3,5-trimethylbenzene (TMB)
in the Leipzig aerosol chamber (LEipziger AerosolKammer, LEAK). Oligomer formation was investigated as a function of seed particle acidity and relative humidity. A fraction of heat-decomposable methylglyoxal oligomers of up to 8 % in the produced organic particle mass was found, highlighting the importance of
those oligomers formed solely by methylglyoxal for SOA formation. Overall,
the present study provides a new and suitable method for quantification of
heat-decomposable methylglyoxal oligomers in the aqueous particle phase
A new source of methyl glyoxal in the aqueous phase
Carbonyl compounds are ubiquitous in atmospheric multiphase system
participating in gas, particle, and aqueous-phase chemistry. One important
compound is methyl ethyl ketone (MEK), as it is detected in significant
amounts in the gas phase as well as in cloud water, ice, and rain.
Consequently, it can be expected that MEK influences the liquid-phase
chemistry. Therefore, the oxidation of MEK and the formation of
corresponding oxidation products were investigated in the aqueous phase.
Several oxidation products were identified from the oxidation with OH
radicals, including 2,3-butanedione, hydroxyacetone, and methylglyoxal. The
molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methylglyoxal. Since methylglyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methylglyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp = 5 × 10−5 s−1), 2,3-butanedione (kp = 9 × 10−6 s−1), methylglyoxal (kp = 3 × 10−5 s−1), and hydroxyacetone (kp = 2 × 10−5 s−1). From the model predictions, a branching ratio of 60 /40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methylglyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methylglyoxal precursor compound for the first time