In principle, calculation of a full Green’s function in any field theory requires knowledge of the infinite set of multipoint Green’s functions, unless one can find some way of truncating the corresponding Schwinger-Dyson equations. For the fermion and boson propagators in QED this requires an ansatz for the full 3-point vertex. Here we illustrate how the properties of gauge invariance, gauge covariance and multiplicative renormalizability impose severe constraints on this fermion-boson interaction, allowing a consistent truncation of the propagator equations. We demonstrate how these conditions imply that the 3-point vertex in the propagator equations is largely determined by the behavior of the fermion propagator itself and not by knowledge of the many higher-point functions. We give an explicit form for the fermion-photon vertex, which in the fermion and photon propagator fulfills these constraints to all orders in leading logarithms for massless QED, and accords with the weak coupling limit in perturbation theory at $\mathcal{O}(\alpha )$. This provides the first attempt to deduce nonperturbative Feynman rules for strong physics calculations of propagators in massless QED that ensure a more consistent truncation of the 2-point Schwinger-Dyson equations. The generalization to next-to-leading order and masses will be described in a longer publication.

We discuss the production of gravity waves from the fragmentation of a supersymmetric condensate in the early Universe. Supersymmetry predicts the existence of flat directions in the potential. At the end of inflation, the scalar fields develop large time-dependent vacuum expectation values along these flat directions. Under some general conditions, the scalar condensates undergo a fragmentation into nontopological solitons, $Q$-balls. We study this process numerically and confirm the recent analytical calculations showing that it can produce gravity waves observable by the Advanced Laser Interferometer Gravitational Wave Observatory, Laser Interferometer Space Antenna, and Big Bang Observer. The fragmentation can generate gravity waves with an amplitude as large as ${\Omega }_{\mathrm{GW}}{h}^2\sim {10}^{-11}$ and with a peak frequency ranging from 1 mHz to 10 Hz, depending on the parameters. The discovery of such a relic gravitational background radiation can open a new window on the physics at the high scales, even if supersymmetry is broken well above the electroweak scale.

We report the results of a first study that uses numerical simulations to estimate the accuracy with which one can use gravitational wave observations of double neutron-star inspiral to measure parameters of the neutron-star equation of state. The simulations use the evolution and initial-data codes of Shibata and Uryū to compute the last several orbits and the merger of neutron stars, with matter described by a parametrized equation of state. Previous work suggested the use of an effective cutoff frequency to place constraints on the equation of state. We find, however, that greater accuracy is obtained by measuring departures from the point-particle limit of the gravitational waveform produced during the late inspiral. As the stars approach their final plunge and merger, the gravitational wave phase accumulates more rapidly for smaller values of the neutron-star compactness (the ratio of the mass of the neutron-star to its radius). We estimate that realistic equations of state will lead to gravitational waveforms that are distinguishable from point-particle inspirals at an effective distance (the distance to an optimally oriented and located system that would produce an equivalent waveform amplitude) of 100 Mpc or less. As Lattimer and Prakash observed, neutron-star radius is closely tied to the pressure at density not far above nuclear. Our results suggest that broadband gravitational wave observations at frequencies between 500 and 1000 Hz will constrain this pressure, and we estimate the accuracy with which it can be measured. Related first estimates of radius measurability show that the radius can be determined to an accuracy of $\delta R\sim 1\mathrm{km}$ at 100 Mpc.

We introduce a parametrized high-density equation of state (EOS) in order to systematize the study of constraints placed by astrophysical observations on the nature of neutron-star matter. To obtain useful constraints, the number of parameters must be smaller than the number of EOS-related neutron-star properties measured, but large enough to accurately approximate the large set of candidate EOSs. We find that a parametrized EOS based on piecewise polytropes with 3 free parameters matches, to about 4% rms error, an extensive set of candidate EOSs at densities below the central density of $1.4M_{\odot }$ stars. Adding observations of more massive stars constrains the higher-density part of the EOS and requires an additional parameter. We obtain constraints on the allowed parameter space set by causality and by present and near-future astronomical observations with the least model dependence. Stringent constraints on the EOS parameter space are associated with the future measurement of the moment of inertia of PSR J0737-3039A combined with the maximum known neutron-star mass. We also present in an appendix a more efficient algorithm than has previously been used for finding points of marginal stability and the maximum angular velocity of stable stars.

We extend the pure pseudo-power-spectrum formalism proposed recently in the context of the cosmic microwave background polarized power spectra estimation by Smith (2006) to incorporate cross-spectra computed for multiple maps of the same sky area. We present an implementation of such a technique, paying particular attention to a calculation of the relevant window functions and mixing (mode-coupling) matrices. We discuss the relevance and treatment of the residual $E/B$ leakage for a number of considered sky apodizations as well as compromises and assumptions involved in an optimization of the resulting power spectrum uncertainty. In particular, we investigate the importance of a pixelization scheme, patch geometry, and sky signal priors used in apodization optimization procedures. In addition, we also present results derived for more realistic sky scans as motivated by the proposed balloon-borne experiment EBEX. We conclude that the presented formalism, thanks to its speed and efficiency, can provide an interesting alternative to the CMB polarized power spectra estimators based on the optimal methods at least on angular scales smaller than $\sim 10°$. In this regime, we find that it is capable of suppressing the total variance of the estimated $B$-mode spectrum to within a factor of $\sim 2$ of the variance due to only the sampling and noise uncertainty of the $B$ modes alone, as derived from the Fisher matrix approach.

This paper is the third in a series investigating the possibility that if we reside in an inflationary “bubble universe,” we might observe the effects of collisions with other such bubbles. Here, we study the interior structure of a bubble collision spacetime, focusing on the issue of where observers can reside. Numerical simulations indicate that if the interbubble domain wall accelerates away, infinite spacelike surfaces of homogeneity develop to the future of the collision; this strongly suggests that observers can have collisions to their past, and previous results then imply that this is very likely. However, for observers at nearly all locations, the restoration of homogeneity relegates any observable effects to a vanishingly small region on the sky. We find that bubble collisions may also play an important role in defining measures in inflation: a potentially infinite relative volume factor arises between two bubble types depending on the sign of the acceleration of the domain wall between them; this may in turn correlate with observables such as the scale or type of inflation.

We analyze all possible extensions of the recently proposed minimal renormalizable SUSY $SU(5)$ grand unified model with the inclusion of an additional $A_4$ flavor symmetry. We find that there are five possible cases but only one of them is phenomenologically interesting. We develop in detail such case and we show how the fermion masses and mixing angles come out. As a prediction we obtain the neutrino masses of order of 0.1 eV with an inverted hierarchy.

We determine the widths of three-body decays of sleptons, ${\tilde{\ell }}^{-}\to {\tilde{\ell }}^{\pm }{\ell }^{-}{\ell }^{\mp }$, ${\tilde{\ell }}^{-}\nu \overline{\nu }$, ${\tilde{\ell }}^{-}q\overline{q}$, in the presence of arbitrary slepton flavor violation and left-right mixing. These decays are important in scenarios in which the lightest supersymmetric particle is the gravitino, a generic possibility in models with gauge- and gravity-mediated supersymmetry breaking. Three-body decays have been discussed previously, assuming flavor conservation and left-right mixing in only the stau sector. Flavor violation and general left-right mixing open up many new decay channels, which provide new avenues for precision mass measurements and may play an essential role in solving the standard model flavor problem. We present results for toy models with two-generation mixing, and discuss the implementation of these results in spice, a program that simplifies collider event simulations of flavor-violating supersymmetric models.

We measure the vacuum energy of two-dimensional $\mathcal{N}=(2,2)$ super Yang-Mills theory using lattice simulation. The obtained vacuum energy density is ${\mathcal{E}}_0=0.09(9)(\genfrac{}{}{0ex}{}{+10}{-8})g^2$, where the first error is the systematic and the second is the statistical one, measured in the dimensionful gauge coupling $g$ which governs the scale of the system. The result is consistent with unbroken supersymmetry, although we cannot exclude a possible very small nonzero vacuum energy.

Using recent results obtained within the hidden gauge formalism for vector mesons, in which the $f_0(1370)$ and $f_2(1270)$ resonances are dynamically generated resonances from the $\rho \rho$ interaction, we evaluate the radiative decay of these resonances into $\gamma \gamma$. We obtain results for the width in good agreement with the experimental data for the $f_2(1270)$ state and a width about a factor 2 smaller for the $f_0(1370)$ resonance, which is also in agreement with the data of the Crystal Ball Collaboration and with the more recent ones from the Belle Collaboration, which, however, have a very large uncertainty.

We study the nonsinglet evolution for the twist-three quark-gluon correlation functions associated with the transverse momentum odd quark distributions. Different from that for the leading-twist quark distributions, these evolution equations involve more general twist-three functions beyond the correlation functions themselves. They provide important information on nucleon structure and can be studied in the semi-inclusive hadron production in deep inelastic scattering and Drell-Yan lepton pair production in the $pp$ scattering process.

The mass differences and mixing angles of neutrinos can neither be explained by R-parity violating split supersymmetry nor by flavor blind quantum gravity alone. It is shown that combining both effects leads, within the allowed parameter range, to good agreement with the experimental results. The atmospheric mass is generated by supersymmetry through mixing between neutrinos and neutralinos, while the solar mass is generated by gravity through flavor blind dimension five operators. Maximal atmospheric mixing forces the tangent squared of the solar angle to be equal to $1/2$. The scale of the quantum gravity operator is predicted within a 5% error, implying that the reduced Planck scale should lie around the grand unified theory scale. In this way, the model is very predictive and can be tested at future experiments.

We report the development of a proton identification method for the Super-Kamiokande (SK) detector. This new tool is applied to the search for events with a single proton track, a high purity neutral current sample of interest for sterile neutrino searches. After selection using a neural network, we observe 38 events in the combined SK-I and SK-II data corresponding to 22 85.1 days of exposure, with an estimated signal-to-background ratio of 1.6 to 1. Proton identification was also applied to a direct search for charged-current quasielastic (CCQE) events, obtaining a high precision sample of fully kinematically reconstructed atmospheric neutrinos, which has not been previously reported in water Cherenkov detectors. The CCQE fraction of this sample is 55%, and its neutrino (as opposed to antineutrino) fraction is $91.7\pm 3\%$. We selected $78\mu$-like and 47 $e$-like events in the SK-I and SK-II data set. With this data, a clear zenith angle distortion of the neutrino direction itself is reported in a sub-GeV sample of $\mu$ neutrinos where the lepton angular correlation to the incoming neutrino is weak. Our fit to ${\nu }_{\mu }\to {\nu }_{\tau }$ oscillations using the neutrino $\frac{L}{E}$ distribution of the CCQE sample alone yields a wide acceptance region compatible with our previous results and excludes the no-oscillation hypothesis at 3-sigma.

The near-horizon metric for a black brane in anti–de Sitter space and the metric near the AdS boundary both exhibit hydrodynamic behavior. We demonstrate the equivalence of this pair of hydrodynamic systems for the sound mode of a conformal theory. This is first established for Einstein’s gravity, but we then show how the sound damping constant will be modified from its Einstein form for a generalized theory. The modified damping constant is expressible as the ratio of a pair of gravitational couplings that are indicative of the sound-channel class of gravitons. This ratio of couplings differs from both that of the shear diffusion coefficient and the shear viscosity to entropy ratio. Our analysis is mostly limited to conformal theories, but suggestions are made as to how this restriction might eventually be lifted.

The one-loop renormalizability of the electroweak sector of the standard model extension (SME) with Lorentz violation is studied. Functional determinants are used to calculate the one-loop contributions of the Higgs, gauge bosons and fermions to the one-loop effective action. The results are consistent with multiplicative renormalization of the SME coupling constants. Conventional electroweak symmetry breaking is effectively unaltered relative to the standard case as the renormalized SME parameters are sufficient to absorb all infinite contributions.

Under dimensional reduction, a system in $D$ spacetime dimensions will not necessarily yield its $D-1$-dimensional analog version. Among other things, this result will depend on the boundary conditions and the dimension $D$ of the system. We investigate this question for scalar and Abelian gauge fields under boundary conditions that obey the symmetries of the action. We apply our findings to the Casimir piston, an ideal system for detecting boundary effects. Our investigation is not limited to extra dimensions and we show that the original piston scenario proposed in 2004, a toy model involving a scalar field in $3D$ ($2+1$) dimensions, can be obtained via dimensional reduction from a more realistic $4D$ electromagnetic (EM) system. We show that for perfect conductor conditions, a $D$-dimensional EM field reduces to a $D-1$ scalar field and not its lower-dimensional version. For Dirichlet boundary conditions, no theory is recovered under dimensional reduction and the Casimir pressure goes to zero in any dimension. This “zero Dirichlet” result is useful for understanding the EM case. We then identify two special systems where the lower-dimensional version is recovered in any dimension: systems with perfect magnetic conductor (PMC) and Neumann boundary conditions. We show that these two boundary conditions can be obtained from a variational procedure in which the action vanishes outside the bounded region. The fields are free to vary on the surface and have zero modes, which survive after dimensional reduction.

We study anisotropic cosmology in Hořava’s gravity theory and obtain Kasner-type solutions, valid for any number, $d$, of spatial dimensions. The corresponding exponents satisfy two relations, one involving the marginal coupling $\lambda$. Also, Hořava’s (super)renormalizable theory predicts (super)stiff matter whose equation of state is $p=w\rho$, with $w\ge 1$. We discuss briefly the implications of these results for the nature of cosmological collapse.

We investigate the geometrical properties of static vacuum $p$-brane solutions of Einstein gravity in $D=n+p+3$ dimensions, which have spherical symmetry of $S^{n+1}$ orthogonal to the $p$ directions and which are invariant under the translation along them. The solutions are characterized by the mass density and $p$ number of tension densities. The causal structure of the higher-dimensional solutions is essentially the same as that of the five-dimensional ones. Namely, a naked singularity appears for most solutions except for the Schwarzschild black $p$-brane and the Kaluza-Klein bubble. We show that some important geometric properties such as the area of $S^{n+1}$ and the total spatial volume are characterized only by the three parameters (the mass density, the sum of tension densities, and the sum of tension density squares), rather than individual tension densities. These geometric properties are analyzed in detail in this parameter space and are compared with those of the five-dimensional case.

A recent measurement of ${}^4\mathrm{He}$ photodisintegration reactions, ${}^4\mathrm{He}(\gamma ,p){}^3\mathrm{H}$ and ${}^4\mathrm{He}(\gamma ,n){}^3\mathrm{He}$ with laser-Compton photons shows smaller cross sections than those estimated by other previous experiments at $E_{\gamma }\lesssim 30\mathrm{MeV}$. We study big bang nucleosynthesis with the radiative particle decay using the new photodisintegration cross sections of ${}^4\mathrm{He}$ as well as previous data. The sensitivity of the yields of all light elements D, T, ${}^3\mathrm{He}$, ${}^4\mathrm{He}$, ${}^6\mathrm{Li}$, ${}^7\mathrm{Li}$, and ${}^7\mathrm{Be}$ to the cross sections is investigated. The change of the cross sections has an influence on the nonthermal yields of D, ${}^3\mathrm{He}$, and ${}^4\mathrm{He}$. On the other hand, the nonthermal ${}^6\mathrm{Li}$ production is not sensitive to the change of the cross sections at this low energy, since the nonthermal secondary synthesis of ${}^6\mathrm{Li}$ needs energetic photons of $E_{\gamma }\gtrsim 50\mathrm{MeV}$. The nonthermal nucleosynthesis triggered by the radiative particle decay is one of candidates of the production mechanism of ${}^6\mathrm{Li}$ observed in metal-poor halo stars. In the parameter region of the radiative particle lifetime and the emitted photon energy, which satisfies the ${}^6\mathrm{Li}$ production above the abundance level observed in metal-poor halo stars, the change of the photodisintegration cross sections at $E_{\gamma }\lesssim 30\mathrm{MeV}$ as measured in the recent experiment leads to $\sim 10\%$ reduction of resulting ${}^3\mathrm{He}$ abundance, whereas the ${}^6\mathrm{Li}$ abundance does not change for this change of the cross sections of ${}^4\mathrm{He}(\gamma ,p){}^3\mathrm{H}$ and ${}^4\mathrm{He}(\gamma ,n){}^3\mathrm{He}$. The ${}^6\mathrm{Li}$ abundance, however, could show a sizable change and therefore the future precise measurement of the cross sections at high energy $E_{\gamma }\gtrsim 50\mathrm{MeV}$ is highly required.

In this paper, we propose and implement on WMAP 5 yr data a model independent approach of foreground power spectrum estimation for multifrequency observations of the CMB experiments. Recently, a model independent approach of CMB power spectrum estimation was proposed by Saha et al. 2006. This methodology demonstrates that the CMB power spectrum can be reliably estimated solely from WMAP data without assuming any template models for the foreground components. In the current paper, we extend this work to estimate the galactic foreground power spectrum using the WMAP 5 yr maps following a self-contained analysis. We apply the model independent method in harmonic basis to estimate the foreground power spectrum and frequency dependence of combined foregrounds. We also study the behavior of synchrotron spectral index variation over different regions of the sky. We use the full sky Haslam map as an external template to increase the degrees of freedom, while computing the synchrotron spectral index over the frequency range from 408 MHz to 94 GHz. We compare our results with those obtained from maximum entropy method foreground maps, which are formed in pixel space. We find that relative to our model independent estimates maximum entropy method maps overestimate the foreground power close to galactic plane and underestimates it at high latitudes.