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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
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DOE OSTI2010

Dynamical generation of pseudoscalar resonances

We study the interactions between the f{sub 0}(980) and a{sub 0}(980) scalar resonances and the lightest pseudoscalar mesons. We first obtain the elementary interaction amplitudes, or interacting kernels, without including any ad hoc free parameter. This is achieved by using previous results on the nature of the lightest scalar resonances as dynamically generated from the rescattering of S-wave two-meson pairs. Afterwards, the interaction kernels are unitarized and the final S-wave amplitudes result. We find that these interactions are very rich and generate a large amount of pseudoscalar resonances that could be associated with the K(1460), {pi}(1300), {pi}(1800), {eta}(1475), and X(1835). We also consider the exotic channels with isospin 3/2 and 1, the latter having positive G-parity. The former could also be resonant in agreement with a previous prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Pion condensation in holographic QCD

We study pion condensation at zero temperature in a hard-wall holographic model of hadrons with isospin chemical potential. We find that the transition from the hadronic phase to the pion condensate phase is first order except in a certain limit of model parameters. Our analysis suggests that immediately across the phase boundary the condensate acts as a stiff medium approaching the Zel'dovich limit of equal energy density and pressure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Nambu-Jona-Lasinio model description of weakly interacting Bose condensate and BEC-BCS crossover in dense QCD-like theories

QCD-like theories possess a positively definite fermion determinant at finite baryon chemical potential {mu}{sub B} and the lattice simulation can be successfully performed. While the chiral perturbation theories are sufficient to describe the Bose condensate at low density, to describe the crossover from Bose-Einstein condensation (BEC) to BCS superfluidity at moderate density we should use some fermionic effective model of QCD, such as the Nambu-Jona-Lasinio model. In this paper, using two-color two-flavor QCD as an example, we examine how the Nambu-Jona-Lasinio model describes the weakly interacting Bose condensate at low density and the BEC-BCS crossover at moderate density. Near the quantum phase transition point {mu}{sub B}=m{sub {pi}} (m{sub {pi}} is the mass of pion/diquark multiplet), the Ginzburg-Landau free energy at the mean-field level can be reduced to the Gross-Pitaevskii free energy describing a weakly repulsive Bose condensate with a diquark-diquark scattering length identical to that predicted by the chiral perturbation theories. The Goldstone mode recovers the Bogoliubov excitation in weakly interacting Bose condensates. The results of in-medium chiral and diquark condensates predicted by chiral perturbation theories are analytically recovered. The BEC-BCS crossover and meson Mott transition at moderate baryon chemical potential as well as the beyond-mean-field corrections are studied. Part of our results can also be applied to real QCD at finite baryon or isospin chemical potential.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Chiral extrapolation of light resonances from one and two-loop unitarized chiral perturbation theory versus lattice results

We study the pion mass dependence of the {rho}(770) and f{sub 0}(600) masses and widths from one and two-loop unitarized chiral perturbation theory (ChPT). We show the consistency of one-loop calculations with lattice results for the M{sub {rho}}, f{sub {pi}}, and the isospin-2 scattering length a{sub 20}. Then, we develop and apply the modified inverse amplitude method formalism for two-loop ChPT. In contrast to the f{sub 0}(600), the {rho}(770) is rather sensitive to the two-loop ChPT parameters--our main source of systematic uncertainty. We thus provide two-loop unitarized fits constrained by lattice information on M{sub {rho}}, f{sub {pi}}, by the qq leading 1/N{sub c} behavior of the {rho} and by existing estimates of low-energy constants. These fits yield relatively stable predictions up to m{sub {pi}{approx_equal}3}00-350 MeV for the {rho} coupling and width as well as for all the f{sub 0}(600) parameters. We confirm, to two loops, the weak m{sub {pi}} dependence of the {rho} coupling and the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin relation, and the existence of two virtual f{sub 0}(600) poles for sufficiently high m{sub {pi}}. At two loops one of these poles becomes a bound state when m{sub {pi}} is somewhat larger than 300 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Direct CP violation for B{sub s}{sup 0}{yields}K{sup 0}{pi}{sup +}{pi}{sup -} decay in QCD factorization

In the framework of QCD factorization, based on the first order of isospin violation, we study direct CP violation in the decay of B{sub s}{sup 0}{yields}K{sup 0}{rho}{sup 0}({omega}){yields}K{sup 0}{pi}{sup +}{pi}{sup -}, including the effect of {rho}-{omega} mixing. We find that the CP violating asymmetry is large via the {rho}-{omega} mixing mechanism when the invariant mass of the {pi}{sup +}{pi}{sup -} pair is in the vicinity of the {omega} resonance. For the decay of B{sub s}{sup 0}{yields}K{sup 0}{rho}{sup 0}({omega}){yields}K{sup 0}{pi}{sup +}{pi}{sup -}, the maximum CP violating asymmetries can reach about 46%. We also discuss the possibility to observe the predicted CP violating asymmetries at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Random matrix model at nonzero chemical potentials with anomaly effects

Phase diagram of the chiral random matrix model with U(1){sub A} breaking term is studied with the quark chemical potentials varied independently at zero temperature by taking the chiral and meson condensates as the order parameters. Although, without the U(1){sub A} breaking term, chiral transition of each flavor can happen separately responding to its chemical potential, the U(1){sub A} breaking terms mix the chiral condensates and correlate the phase transitions. In the three-flavor case, we find that there are mixings between the meson and chiral condensates due to the U(1){sub A} anomaly, which makes the meson condensed phase more stable. Increasing the hypercharge chemical potential ({mu}{sub Y}) with the isospin and quark chemical potentials ({mu}{sub I},{mu}{sub q}) kept small, we observe that the kaon-condensed phase becomes the ground state and at the larger {mu}{sub Y} the pion-condensed phase appears unexpectedly, which is caused by the competition between the chiral restoration and the meson condensation. The similar happens when {mu}{sub Y} and {mu}{sub I} are exchanged, and the kaon-condensed phase becomes the ground state at larger {mu}{sub I} below the full chiral restoration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Tests of factorization and SU(3) relations in B decays into heavy-light final states

Using data from the B factories and the Tevatron, we perform tests of how well nonleptonic B decays of the kind B{yields}D{sub (s)}{sup (*)}P, where P is a pion or kaon, are described within the factorization framework. We find that factorization works well--as is theoretically expected--for color-allowed, tree-diagram-like topologies. Moreover, also exchange topologies, which have a nonfactorizable character, do not show any anomalous behavior. We discuss also isospin triangles between the B{yields}D{sup (*)}{pi} decay amplitudes, and determine the corresponding amplitudes in the complex plane, which show a significant enhancement of the color-suppressed tree contribution with respect to the factorization picture. Using data for B{yields}D{sup (*)}K decays, we determine SU(3)-breaking effects and cannot resolve any nonfactorizable SU(3)-breaking corrections larger than {approx}5%. In view of these results, we point out that a comparison between the B{sub d}{sup 0}{yields}D{sup +}{pi}{sup -} and B{sub s}{sup 0}{yields}D{sub s}{sup +}{pi}{sup -} decays offers an interesting new determination of f{sub d}/f{sub s}. Using CDF data, we obtain the most precise value of this ratio at CDF, and discuss the prospects for a corresponding measurement at LHCb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Possible BK molecular structure of B{sub s0}*(5725) in the Bethe-Salpeter approach

We interpret the scalar B{sub s0}*(5725) as an S-wave BK molecular bound state in the Bethe-Salpeter approach. In the ladder and instantaneous approximation, with the kernel induced by {rho} and {omega} exchanges, we establish the Bethe-Salpeter equation for B{sub s0}*(5725). We find that the bound state of BK can exist. We also calculate the isospin-violating decay width of the process B{sub s0}*(5725){yields}B{sub s}{pi}{sup 0} through exchanging K{sup *} and B{sup *} mesons including the {eta}-{pi}{sup 0} mixing effect. We hope that the obtained decay width is instructive for the forthcoming experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Calculating kaon fragmentation functions from the Nambu-Jona-Lasinio jet model

The Nambu-Jona-Lasinio (NJL)-jet model provides a sound framework for calculating the fragmentation functions in an effective chiral quark theory, where the momentum and isospin sum rules are satisfied without the introduction of ad hoc parameters. Earlier studies of the pion fragmentation functions using the NJL model within this framework showed qualitative agreement with the empirical parametrizations. Here we extend the NJL-jet model by including the strange quark. The corrections to the pion fragmentation functions and corresponding kaon fragmentation functions are calculated using the elementary quark to quark-meson fragmentation functions from NJL. The results for the kaon fragmentation functions exhibit a qualitative agreement with the empirical parametrizations, while the unfavored strange quark fragmentation to pions is shown to be of the same order of magnitude as the unfavored light quark. The results of these studies are expected to provide important guidance for the analysis of a large variety of semi-inclusive data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Pion-pion scattering amplitude. IV. Improved analysis with once subtracted Roy-like equations up to 1100 MeV

We improve our description of {pi}{pi} scattering data by imposing additional requirements on our previous fits, in the form of once-subtracted Roy-like equations, while extending our analysis up to 1100 MeV. We provide simple and ready to use parametrizations of the amplitude. In addition, we present a detailed description and derivation of these once-subtracted dispersion relations that, in the 450 to 1100 MeV region, provide an additional constraint which is much stronger than our previous requirements of forward dispersion relations and standard Roy equations. The ensuing constrained amplitudes describe the existing data with rather small uncertainties in the whole region from threshold up to 1100 MeV, while satisfying very stringent dispersive constraints. For the S0 wave, this requires an improved matching of the low and high energy parametrizations. Also for this wave we have considered the latest low energy K{sub l4} decay results, including their isospin violation correction, and we have removed some controversial data points. These changes on the data translate into better determinations of threshold and subthreshold parameters which remove almost all disagreement with previous chiral perturbation theory and Roy equation calculations below 800 MeV. Finally, our results favor the dip structure of the S0 inelasticity around the controversial 1000 MeV region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Scheme for the extraction of WIMP-nucleon scattering cross sections from total event rates

We propose a scheme that allows to analytically determine the three elementary cross sections and connect the solutions to the relative sign between the proton and the neutron spin scattering amplitudes once the measurements of total event rate from three appropriate targets become available. In this way it is thus possible to extract the maximum information on the supersymmetric parameter space obtainable from direct detection experiments, in the case that the dark matter particle is the lightest neutralino. Our scheme is based on suitably normalized forms of the isospin momentum dependent structure functions entering in the spin-dependent elastic neutralino-nucleus cross section. We compare these functions with the commonly used ones and discuss their advantages: in particular, these allow in the spin-dependent cross section to factorize the particle physics degrees of freedom from the momentum transfer dependent nuclear structure functions as it happens in the spin-independent cross section with the nuclear form factor.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Testing Higgs models via the H{sup {+-}}W{sup {-+}}Z vertex by a recoil method at the International Linear Collider

In general, charged Higgs bosons H{sup {+-}} appear in nonminimal Higgs models. The H{sup {+-}}W{sup {-+}}Z vertex is known to be related to the violation of the global symmetry (custodial symmetry) in the Higgs sector. Its magnitude strongly depends on the structure of the exotic Higgs models which contain higher isospin SU(2){sub L} representations such as triplet Higgs bosons. We study the possibility of measuring the H{sup {+-}}W{sup {-+}}Z vertex via single charged Higgs boson production associated with the W{sup {+-}} boson at the International Linear Collider (ILC) by using the recoil method. The feasibility of the signal e{sup +}e{sup -}{yields}H{sup {+-}}W{sup {-+}}{yields}l{nu}jj is analyzed assuming the polarized electron and positron beams and the expected detector performance for the resolution of the two-jet system at the ILC. The background events can be reduced to a considerable extent by imposing the kinematic cuts even if we take into account the initial state radiation. For a relatively light charged Higgs boson whose mass m{sub H}{sup {+-}} is in the region of 120-130 GeV <m{sub H}{sup {+-}}<m{sub W}+m{sub Z}, the H{sup {+-}}W{sup {-+}}Z vertex would be precisely testable especially when the decay of H{sup {+-}} is lepton specific. The exoticness of the extended Higgs sector can be explored by using combined information for this vertex and the rho parameter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Instanton effects on the twist-three light-cone distribution amplitudes of pion and light scalar mesons above 1 GeV

By use of a single-instanton approximation the twist-three light-cone distribution amplitudes of the pion as well as the p-wave mesons, i.e., f{sub 0}(1370), K{sub 0}*(1430), and a{sub 0}(1450), are investigated within the framework of QCD moment sum rules with the inclusion of instanton effects based on the valence quark model. The results show that there is much change on light-cone distribution amplitudes due to the isospin- and chirality-dependent instanton contribution compared with the instanton-free ones. We find that the instanton-involved twist-three light-cone distribution amplitudes are non-positive-definite within some range of the momentum fraction and that there are rapid changes at two ends of the momentum fraction. To guarantee the convergence of moments using the method in this work, a low instanton density should be adopted; for instance, n{sub c}=(1/2) fm{sup -4}. Possible ingredients which might have an impact on the results are briefly discussed. These light-cone distribution amplitudes may be helpful to analyze exclusive heavy-flavored processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Hadron-quark phase transition in asymmetric matter with dynamical quark masses

The two-equation-of-state model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor Nambu-Jona-Lasinio effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed-current quark masses, the main important effect of the chiral dynamics is the appearance of an end point for the coexistence zone. We show that a first-order hadron-quark phase transition may take place in the region T subset of (50-80) MeV and {rho}{sub B} subset of (2-4){rho}{sub 0}, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From the isospin properties of the mixed phase, some possible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of a critical end point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Fermiophobia in a Higgs triplet model

A fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in two higgs doublet models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass, a characteristic signal would be a moderate B(H{yields}{gamma}{gamma}) accompanied by a large B(H{yields}JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H{yields}ZZ, WW and suppressed H{yields}JJ decay modes. In this situation, B(H{yields}ZZ) is larger than B(H{yields}WW), which differs from the SM prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Improved stochastic estimation of quark propagation with Laplacian Heaviside smearing in lattice QCD

A new method of stochastically estimating the low-lying effects of quark propagation is proposed which allows accurate determinations of temporal correlations of single-hadron and multihadron operators in lattice QCD. The method is well suited for calculations in large volumes. Contributions involving quark propagation connecting hadron sink operators at the same final time can be handled in a straightforward manner, even for a large number of final time slices. The method exploits Laplacian Heaviside (LapH) smearing. Z{sub N} noise is introduced in a novel way, and variance reduction is achieved using judiciously-chosen noise-dilution projectors. The method is tested using isoscalar mesons in the scalar, pseudoscalar, and vector channels, and using the two-pion system of total isospin I=0, 1, 2 on large anisotropic 24{sup 3}x128 lattices with spatial spacing a{sub s}{approx}0.12 fm and temporal spacing a{sub t}{approx}0.034 fm for pion masses m{sub {pi}}{approx_equal}390 and 240 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗