Search

The temperature dependence of the sum of the QCD up- and down-quark masses, (mu + md) and the pion decay constant fπ, are determined from two thermal finite energy QCD sum rules for the pseudoscalar-current correlator. This quark mass remains mostly constant for temperatures well below the critical temperature for deconfinement/chiral-symmetry restoration. As this critical temperature is approached, the quark mass increases sharply with increasing temperature. This increase is far more pronounced if the temperature dependence of the pion mass (determined independently from other methods) is taken into account. The behavior of fπ(T) is consistent with the expectation from chiral symmetry, i.e. that it should follow the thermal dependence of the quark condensate, independently of the quark mass. [ABSTRACT FROM AUTHOR]

We consider a model where the standard model is extended by the addition of a vector-like isosinglet down-type quark b ′ . We perform a χ 2 fit to the flavor physics data and obtain the preferred central values along with errors of all the elements of the measurable 3 × 4 quark mixing matrix. The fit indicates that all the new-physics parameters are consistent with zero and the mixing of the b ′ quark with the other three is constrained to be small. The current flavor physics data rules out possibility of detectable new physics signals in most of the flavor physics observables. We also investigate possible deviations in the standard model Wtb couplings and bottom quark coupling to Higgs boson. We find that these deviations are less than a percent level which is too small to be observed at the LHC with current precision. [ABSTRACT FROM AUTHOR]

I describe how nuclear structure can be predicted from lattice QCD through low-energy effective field theories, using as an example a world simulation with relatively heavy up and down quarks. [ABSTRACT FROM AUTHOR]

Background: The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. Purpose: In this work, we extract the proton and neutron form factors from worldwide data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucléon. From these, we separate the up- and down-quark contributions to the proton form factors. Method: We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parametrization of the neutron form factor data and uncertainties to separate the up- and down-quark contributions to the proton's charge and magnetic form factors. Results: The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavorseparated form factors are extracted and compared to models of the nucleon structure. Conclusions: With the inclusion of the precise new data, the extracted TPE contributions show a clear change of sign at low Q², which is necessary to explain the high-Q² form factor discrepancy while being consistent with the known Q² → 0 limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavor-separated contributions. We also observe that the rms radius of both the up and down-quark distributions are smaller than the rms charge radius of the proton. [ABSTRACT FROM AUTHOR]

Two aspects of isospin breaking in the decay $$K^\pm \rightarrow \pi ^0 \pi ^0 e^\pm \mathop {\nu _e}\limits ^{_{(-)}}$$ are studied and discussed. The first addresses the possible influence of the phenomenological description of the unitarity cusp on the extraction of the normalization of the form factor from data. Using the scalar form factor of the pion as a theoretical laboratory, we find that this determination is robust under variations of the phenomenological parameterizations of the form factor. The second aspect concerns the issue of radiative corrections. We compute the radiative corrections to the total decay rate for $$K^\pm \rightarrow \pi ^0 \pi ^0 e^\pm \mathop {\nu _e}\limits ^{_{(-)}}$$ in a setting that allows comparison with the way radiative corrections were handled in the channel $$K^\pm \rightarrow \pi ^+ \pi ^- e^\pm \mathop {\nu _e}\limits ^{_{(-)}}$$ . We find that, once radiative corrections are included, the normalizations of the form factor as determined experimentally from data in the two decay channels come to a better agreement. The remaining discrepancy can easily be accounted for by other isospin-breaking corrections, mainly those due to the difference between the masses of the up and down quarks. [ABSTRACT FROM AUTHOR]

We point out that the hypothesis of an SU ( 5 ) -like supersymmetric Grand Unified Theory (GUT) implies a generic relation within the flavour structure of up-type squarks. Contrary to other well-known SU ( 5 ) relations between the down-quark and charged lepton sectors, this relation remains exact in the presence of any corrections and extra operators. Moreover it remains valid to a good precision at the electroweak scale, and opens thus new possibilities for testing SU ( 5 ) -like GUTs. We derive the low-energy effective theory of observable light up-type squarks, that also constitutes a useful tool for squark phenomenology. We use this effective theory to determine how to test SU ( 5 ) relations at the LHC. Focusing on scenarios with light stops, compatible with Natural SUSY, it appears that simple tests involving ratios of event rates are sufficient to test the hypothesis of an SU ( 5 ) -like GUT theory. The techniques of charm-tagging and top-polarimetry are a crucial ingredient of these tests. [ABSTRACT FROM AUTHOR]

To measure the Yukawa couplings of the up and down quarks, Yu,d, seems to be far beyond the capabilities of current and (near) future experiments in particle physics. By performing a general analysis of the potential misalignment between quark masses and Yukawa couplings, we derive predictions for the magnitude of induced flavor-changing neutral currents (FCNCs), depending on the shift in the physical Yukawa coupling of first-generation quarks. We find that a change of more than 50% in Yd would generically result in ds transitions in conflict with kaon physics. This could already be seen as evidence for a nonvanishing direct coupling of the down quark to the newly discovered Higgs boson. The nonobservation of certain--already well-constrained--processes is thus turned into a powerful indirect measure of otherwise basically unaccessible physical parameters of the effective standard model. Similarly, improvements in limits on FCNCs in the up-type quark sector can lead to valuable information on Yu. [ABSTRACT FROM AUTHOR]

The article focuses on research into conditions which would allow the theoretical particles cold quark matter and strangelets exist. It states protons and neutrons consist of three up and down quarks which are bound by the strong nuclear force. It mentions speculation that inside extreme pressures of neutral stars quarks could break free of strong-force chains and exist as its own form of matter which would include strange quarks. It talks about vacuum energy and superheavy element research.