59034157
On the analytic structure of scalar glueball operators at the Born level
We study the analytic structure of the two-point function of the operator F 2 which is expected to describe a scalar glueball. The calculation of the involved integrals is complicated by nonanalytic structures in the integrands, which we take into account properly by identifying cuts generated by angular integrals and deforming the contours for the radial integration accordingly. The obtained locations of the branch points agree with Cutkosky’s cut rules. As input we use different nonperturbative Landau gauge gluon propagators with different analytic properties as obtained from lattice and functional calculations. All of them violate positivity and describe thus gluons absent from the asymptotic physical space. The resulting spectral densities for the glueball candidate show a cut but no poles for lightlike momenta, which can be attributed to the employed Born approximation.
119167811
The infrared behavior of Landau gauge Yang–Mills theory in d=2, 3 and 4 dimensions
Abstract We develop a general power counting scheme for the infrared limit of Landau gauge SU ( N ) Yang–Mills theory in arbitrary dimensions. Employing a skeleton expansion, we find that the infrared behavior is qualitatively independent of the spacetime dimension d . In the cases d = 2 , 3 and 4 even the quantitative results for the infrared exponents of the vertices differ only slightly. Therefore, corresponding lattice simulations provide interesting qualitative information for the physical case. We furthermore find that the loop integrals depend only weakly on the numerical values of the IR exponents.
86866691
Spurious divergences in Dyson-Schwinger equations
A bstractWe revisit the treatment of spurious ultraviolet divergences in the equation of motion of the gluon propagator caused by a momentum cutoff and the resulting violation of gauge invariance. With present continuum studies of the gluon propagator from its Dyson-Schwinger equation reaching the level of quantitatively accurate descriptions, it becomes increasingly important to understand how to subtract these spurious divergences in an unambiguous way. Here we propose such a method. It is based entirely on the asymptotic perturbative behavior of the QCD Green’s functions without affecting non-perturbative aspects such as mass terms or the asymptotic infrared behavior. As a particular example, this allows us to assess the possible influence of the tadpole diagram beyond perturbation theory. Finally, we test this method numerically by solving the system of Dyson-Schwinger equations of the gluon and ghost propagators.
119208185
Going beyond the propagators of Landau gauge Yang-Mills theory
We present results for the propagators and the ghost-gluon vertex of Landau gauge Yang-Mills theory obtained from Dyson-Schwinger equations. Solving these three quantities simultaneously constitutes a new step in truncating these equations. We also introduce a new model for the three-gluon vertex that is motivated by lattice results. It features a zero crossing which is confirmed a posteriori by a Dyson-Schwinger calculation. Within our setup we can reproduce lattice data very well. We establish that also for the ghost-gluon vertex a difference between decoupling and scaling solutions is present. For the scaling solution we discuss the possibility of modifying the infrared exponents via an angle dependence of the ghost-gluon vertex. However, no such dependence is found in our calculations. Finally, we calculate the Schwinger function for the gluon propagator.
118463320
Infrared analysis of Dyson-Schwinger equations taking into account the Gribov horizon in Landau gauge
The low momentum behavior of the Landau gauge Gribov-Zwanziger action is investigated using the respective Dyson-Schwinger equations. Because of the mixing of the gluon and the auxiliary fields four scenarios can be distinguished for the infrared behavior. Two of them lead to inconsistencies and can be discarded. Another one corresponds to the case where the auxiliary fields behave exactly like the Faddeev-Popov ghosts and the same scaling relation as in standard Landau gauge, {kappa}{sub A}+2{kappa}{sub c}=0, is valid. Even the parameter {kappa} is found to be the same, 0.595. The mixed propagators, which appear, are suppressed in all loops, and their anomalous infrared exponent can also be determined. A fourth case provides an even stricter scaling relation that includes also the mixed propagators, but possesses the same qualitative feature, i.e. the propagators of the Faddeev-Popov ghost and the auxiliary fields are infrared enhanced and the mixed and the gluon propagators are infrared suppressed. In this case the system of equations to obtain the parameter {kappa} is nonlinear in all variables.
118375544
On the influence of three-point functions on the propagators of Landau gauge Yang-Mills theory
A bstractWe solve the Dyson-Schwinger equations of the ghost and gluon propagators of Landau gauge Yang-Mills theory together with that of the ghost-gluon vertex. The latter plays a central role in many truncation schemes for functional equations. By including it dynamically we can determine its influence on the propagators. We also suggest a new model for the three-gluon vertex motivated by lattice data which plays a crucial role to obtain stable solutions when the ghost-gluon vertex is included. We find that both vertices have a sizable quantitative impact on the mid-momentum regime and contribute to the reduction of the gap between lattice and Dyson-Schwinger equation results. Furthermore, we establish that the three-gluon vertex dressing turns negative at low momenta as suggested by lattice results in three dimensions.
119092260
Relativistic entanglement of two massive particles
We describe the spin and momentum degrees of freedom of a system of two massive spin-(1/2) particles as a four-qubit system. Then we explicitly show how the entanglement changes between different partitions of the qubits, when considered by different inertial observers. Although the two particle entanglement corresponding to a partition into Alice's and Bob's subsystems is, as often stated in the literature, invariant under Lorentz boosts, the entanglement with respect to other partitions of the Hilbert space on the other hand, is not. It certainly does depend on the chosen inertial frame and on the initial state considered. The change of entanglement arises, because a Lorentz boost on the momenta of the particles causes a Wigner rotation of the spin, which in certain cases entangles the spin with the momentum states. We systematically investigate the situation for different classes of initial spin states and different partitions of the four-qubit space. Furthermore, we study the behavior of Bell inequalities for different observers and demonstrate how the maximally possible degree of violation, using the Pauli-Lubanski spin observable, can be recovered by any inertial observer.
10284407
OPTICAL CROSS-CORRELATION FILTERS: AN ECONOMICAL APPROACH FOR IDENTIFYING SNe Ia AND ESTIMATING THEIR REDSHIFTS
Large photometric surveys of transient phenomena, such as Panoramic Survey Telescope & Rapid Response System and Large Synoptic Survey Telescope, will locate thousands to millions of Type Ia supernova (SN Ia) candidates per year, a rate prohibitive for acquiring spectroscopy to determine each candidate's type and redshift. In response, we have developed an economical approach to identifying SNe Ia and their redshifts using an uncommon type of optical filter which has multiple, discontinuous passbands on a single substrate. Observation of a supernova through a specially designed pair of these "cross-correlation filters" measures the approximate amplitude and phase of the cross-correlation between the spectrum and a SN Ia template, a quantity typically used to determine the redshift and type of a high-redshift SN Ia. Simulating the use of these filters, we obtain a sample of SNe Ia which is ~98% pure with individual redshifts measured to σ z = 0.01 precision. The advantages of this approach over standard broadband photometric methods are that it is insensitive to reddening, independent of the color data used for subsequent distance determinations which reduce selection or interpretation bias, and because it makes use of the spectral features its reliability is greater. A great advantage over long-slit spectroscopy comes from increased throughput, enhanced multiplexing, and reduced setup time resulting in a net gain in speed of up to ~30 times. This approach is also insensitive to host galaxy contamination. Prototype filters were built and successfully used on Magellan with LDSS-3 to characterize three SuperNova Legacy Survey candidates. We discuss how these filters can provide critical information for the upcoming photometric supernova surveys.
120044649
Position dependence in the CDMS II ZIP detectors
The Ge and Si detectors developed by the Cryogenic Dark Matter Search (CDMS) II experiment rely on the simultaneous detection of athermal phonons and ionization produced by interactions in the crystal. The athermal phonons provide both the total energy deposited in an interaction and the information about the position of the interaction. We describe extracting this information from the pulse shapes in the four phonon sensors. We present the result of measurements made on a Si detector from the first CDMS II production batch. We also investigate ways of using the event position information to extract further information about the phonon signal.
121335171
A study of meson-baryon couplings in the constituent quark model
Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (3P0-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the3P0 vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the3P0-model, only.
15665437
Testing LMC Microlensing Scenarios: The Discrimination Power of the SuperMACHO Microlensing Survey
Characterizing the nature and spatial distribution of the lensing objects that produce the previously measured microlensing optical depth toward the Large Magellanic Cloud (LMC) remains an open problem. We present an appraisal of the ability of the SuperMACHO Project, a next-generation microlensing survey directed toward the LMC, to discriminate between various proposed lensing populations. We consider two scenarios: lensing by a uniform foreground screen of objects and self-lensing by LMC stars. The optical depth for screen lensing is essentially constant across the face of the LMC, whereas the optical depth for self-lensing shows a strong spatial dependence. We have carried out extensive simulations, based on data obtained during the first year of the project, to assess the SuperMACHO survey's ability to discriminate between these two scenarios. In our simulations we predict the expected number of observed microlensing events for various LMC models for each of our fields by adding artificial stars to the images and estimating the spatial and temporal efficiency of detecting microlensing events using Monte Carlo methods. We find that the event rate itself shows significant sensitivity to the choice of the LMC luminosity function, limiting the conclusions that can be drawn from the absolute rate. If instead we determine the differential event rate across the LMC, we will decrease the impact of these systematic biases and render our conclusions more robust. With this approach the SuperMACHO Project should be able to distinguish between the two categories of lens populations. This will provide important constraints on the nature of the lensing objects and their contributions to the Galactic dark matter halo.