We discuss the tension between discrete flavor symmetries and extended scalar sectors arising from lepton flavor violation experiments. The key point is that extended scalar sectors will generically lead to flavor changing neutral currents, which are strongly constrained by experiments. Because of the large parameter space in the scalar sector such models will, however, usually have no big problems with existing and future bounds (even though the models might be constrained). This changes considerably once a flavor symmetry is imposed in addition: Because of the symmetry, additional relations between the different couplings arise and cancellations become impossible in certain cases. The experimental bounds will then constrain the model severely and can easily exclude it. We consider two examples which show how these considerations are realized. The same logic should apply to a much wider class of models.

We report results for the masses of the flavor nonsinglet light $0^{++}$, $1^{--}$, and $1^{+-}$ mesons from unquenched lattice QCD at two lattice spacings. The twisted mass formalism was used with two flavors of sea quarks. For the $0^{++}$ and $1^{+-}$ mesons we look for the effect of decays on the mass dependence. For the light vector mesons we study the chiral extrapolations of the mass. We report results for the leptonic and transverse decay constants of the $\rho$ meson. We test the mass dependence of the KSRF relations, between the mass, leptonic coupling constant, and strong coupling of the rho meson.

We present a calculation of the three-quark core contribution to the mass of the $\Delta$ resonance in a Poincaré-covariant Faddeev framework. A consistent setup for the dressed-quark propagator, the quark-quark and quark-”diquark” interactions is used, where all the ingredients are solutions of their respective Dyson-Schwinger or Bethe-Salpeter equations in rainbow-ladder truncation. We discuss the evolution of the $\Delta$ mass with the current-quark mass and compare to the previously obtained mass of the nucleon.

We calculate bottom-hadron mass splittings with respect to $B_d$ and ${\Lambda }_b$ using full QCD with $2+1$ flavors of dynamical Kogut-Susskind sea quarks and domain-wall valence quarks along with a static heavy quark. Our lattices have spatial volume of $(2.5\mathrm{fm}{)}^3$ with lattice spacing about 0.124 fm and a range of pion masses as low as 291 MeV. Our results are in agreement with experimental observations and other lattice calculations within our statistical and systematic errors. In particular, we find the mass of the ${\Omega }_b$ to be consistent with the recent CDF measurement. We also predict the mass for the as yet unobserved ${\Xi }_b^{\prime }$ to be 5955(27) MeV.

The results on polarized parton densities obtained using different methods of QCD analysis of the present polarized DIS data are discussed. Their dependence on the method used in the analysis, accounting or not for the kinematic and dynamic $1/Q^2$ corrections to spin structure function $g_1$, is demonstrated. It is pointed out that the precise data in the preasymptotic region require a more careful matching of the QCD predictions to the data in this region in order to determine the polarized parton densities correctly.

We use nonperturbative lattice techniques to study the volume-reduced “Eguchi-Kawai” version of four-dimensional large-$N$ QCD with a single adjoint Dirac fermion. We explore the phase diagram of this single-site theory in the space of quark mass and gauge coupling using Wilson fermions for a number of colors in the range $8\le N\le 15$. Our evidence suggests that these values of $N$ are large enough to determine the nature of the phase diagram for $N\to \infty$. We identify the region in the parameter space where the $(Z_N{)}^4$ center symmetry is intact. According to previous theoretical work using the orbifolding paradigm, and assuming that translation invariance is not spontaneously broken in the infinite-volume theory, in this region volume reduction holds: the single-site and infinite-volume theories become equivalent when $N\to \infty$. We find strong evidence that this region includes both light and heavy quarks (with masses that are at the cutoff scale), and our results are consistent with this region extending toward the continuum limit. We also compare the action density and the eigenvalue density of the overlap Dirac operator in the fundamental representation with those obtained in large-$N$ pure-gauge theory.

We investigate twisted $C$-periodic boundary conditions in $\mathrm{SU}(N)$ gauge field theory with an adjoint Higgs field. We show that with a suitable twist for even $N$ one can impose a nonzero magnetic charge relative to residual U(1) gauge groups in the broken phase, thereby creating a ’t Hooft-Polyakov magnetic monopole. This makes it possible to use lattice Monte Carlo simulations to study the properties of these monopoles in the quantum theory.

In this paper we describe algebraic and diagrammatic methods related to the maximally helicity-violating generating function method for evaluating and exposing the structure of supersymmetric sums over the states crossing generalized unitarity cuts of multiloop amplitudes in four dimensions. We focus mainly on cuts of maximally supersymmetric Yang-Mills amplitudes. We provide various concrete examples, some of which are directly relevant for the calculation of four-loop amplitudes. Additionally, we discuss some cases with less-than-maximal supersymmetry. The results of these constructions carry over to generalized cuts of multiloop supergravity amplitudes through use of the Kawai-Lewellen-Tye relations between gravity and gauge-theory tree amplitudes.

We describe a characteristic signature of dark matter (DM) annihilation or decay into gamma rays. We show that if the total angular momentum of the initial DM particle(s) vanishes, and helicity suppression operates to prevent annihilation/decay into light fermion pairs, then the amplitude for the dominant 3-body final state $f^{+}{f}^{-}\gamma$ has a unique form dictated by gauge invariance. This amplitude and the corresponding energy spectra hold for annihilation of DM Majorana fermions or self-conjugate scalars, and for decay of DM scalars, thus encompassing a variety of possibilities. Within this scenario, we analyze Fermi LAT, PAMELA, and HESS data, and predict a hint in future Fermi gamma-ray data that portends a striking signal at atmospheric Cherenkov telescopes.

We perform a Markov chain Monte Carlo analysis of the self-accelerating and normal branch of Dvali-Gabadadze-Porrati braneworld gravity. By adopting a parametrized post-Friedmann description of gravity, we utilize all of the cosmic microwave background data, including the largest scales, and its correlation with galaxies in addition to the geometrical constraints from supernovae distances and the Hubble constant. We find that on both branches brane tension or a cosmological constant is required at high significance with no evidence for the unique Dvali-Gabadadze-Porrati modifications. The crossover scale must therefore be substantially greater than the Hubble scale $H_0{r}_c>3$ and 3.5 at the 95% C.L. with and without uncertainties from spatial curvature. With spatial curvature, the limit from the normal branch is substantially assisted by the galaxy cross correlation which highlights its importance in constraining infrared modifications to gravity.

One way of avoiding the destabilization of the electroweak scale through a strong coupled regime naturally occurs in models with a Landau-like pole at the TeV scale. Hence, the quadratic divergence contributions to the scalar masses are not considered as a problem anymore since a new nonperturbative dynamic emerges at the TeV scale. This scale should be an intrinsic feature of the models, and there is no need to invoke any other sort of protection for the electroweak scale. In some models based on the $SU(3{)}_C\otimes SU(3{)}_W\otimes U(1{)}_X$ gauge symmetry, a nonperturbative dynamics arise and it stabilizes the electroweak scale.

At the LHC multiple parton interactions will represent an important feature of the minimum bias and of the underlying event, and will give important contributions in many channels of interest in the search for new physics. Different numbers of multiple collisions may contribute to the production of a given final state, and one should expect important interference effects in the regime where different contributions have similar rates. We show, on the contrary, that, once multiple parton interactions are identified by their different topologies, terms with different numbers of multiple parton interactions do not interfere in the final cross section.

We present the first measurement of the energy spectrum up to 70 MeV of electrons from the decay of negative muons after they become bound in ${}^{27}\mathrm{Al}$ atoms. The data were taken with the TWIST apparatus at TRIUMF. We find a muon lifetime of $(864.6\pm 1.2)\mathrm{ns}$, in agreement with earlier measurements. The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarized the muons. The measured momentum spectrum is in reasonable agreement with theoretical predictions at the higher energies, but differences around the peak of the spectrum indicate the need for $\mathcal{O}(\alpha )$ radiative corrections to the calculations. The present measurement is the most precise measurement of the decay spectrum of muons bound to any nucleus.

Based on the strong coupling expansion we obtain effective three-dimensional models for the Polyakov loop in finite temperature $G_2$ gluodynamics. The Svetitsky-Jaffe conjecture relates the resulting continuous spin models with $G_2$ gluodynamics near phase transition points. In the present work we analyze the effective theory in leading order with the help of a generalized mean-field approximation and with detailed Monte Carlo simulations. In addition we derive a Potts-type discrete spin model by restricting the characters of the Polyakov loops to the three extremal points of the fundamental domain of $G_2$. Both the continuous and discrete effective models show a rich phase structure with a ferromagnetic, symmetric and several antiferromagnetic phases. The phase diagram contains first and second order transition lines and tricritical points. The modified mean-field predictions compare very well with the results of our simulations.

We develop a new superfield approach to $\mathcal{N}=4$ supersymmetric mechanics based on the concept of biharmonic superspace (bi-HSS). It is an extension of the $\mathcal{N}=4$, $d=1$ superspace by two sets of harmonic variables associated with the two SU(2) factors of the $R$-symmetry group SO(4) of the $\mathcal{N}=4$, $d=1$ super Poincaré algebra. There are three analytic subspaces in it: two of the Grassmann dimension 2 and one of the dimension 3. They are closed under the infinite-dimensional “large” $\mathcal{N}=4$ superconformal group, as well as under the finite-dimensional superconformal group $D(2,1;\alpha )$. The main advantage of the bi-HSS approach is that it gives an opportunity to treat $\mathcal{N}=4$ supermultiplets with finite numbers of off-shell components on equal footing with their “mirror” counterparts. We show how such multiplets and their superconformal properties are described in this approach. We also define nonpropagating gauge multiplets which can be used to gauge various isometries of the bi-HSS actions. We present an example of a nontrivial $\mathcal{N}=4$ mechanics model with a seven-dimensional target manifold obtained by gauging a U(1) isometry in a sum of the free actions of the multiplet $(\mathbf{4},\mathbf{4},\mathbf{0})$ and its mirror counterpart.

I use the Newtonian equation of hydrostatic equilibrium for an isotropic fluid sphere to generate exact anisotropic solutions of Einstein’s equations. The input function is simply the density. An infinite number of regular solutions are constructed, some of which satisfy all the standard energy conditions. Two classes of these solutions generalize the Newtonian polytropes of index 0 and 1.

Emission coordinates are those generated by positioning systems. Positioning systems are physical systems constituted by four emitters broadcasting their respective times by means of sound or light signals. We analyze the incidence of the space-time causal structure on the construction of emission coordinates. The Newtonian case of four emitters at rest is analyzed and contrasted with the corresponding situation in special relativity.

General relativistic simulations for the merger of binary neutron stars are performed as an extension of a previous work [M. Shibata and K. Taniguchi, Phys. Rev. D 73, 064027 (2006).]. We prepare binary neutron stars with a large initial orbital separation and employ the moving-puncture formulation, which enables one to follow merger and ringdown phases for a long time, even after black hole formation. For modeling inspiraling neutron stars, which should be composed of cold neutron stars, the Akmal-Pandharipande-Ravenhall (APR) equation of state (EOS) is adopted. After the onset of merger, the hybrid-type EOS is used; i.e., the cold and thermal parts are given by the APR and $\Gamma$-law EOSs, respectively. Three equal-mass binaries, each with mass $1.4M_{\odot }$, $1.45M_{\odot }$, and $1.5M_{\odot }$, and two unequal-mass binaries with mass, 1.3 vs $1.6M_{\odot }$ and 1.35 vs $1.65M_{\odot }$, are prepared. We focus primarily on the black hole formation case, and explore mass and spin of the black hole, mass of disks which surround the black hole, and gravitational waves emitted during the black hole formation. We find that (i) the black hole is promptly formed if total mass of the system initially satisfies $m_0\gtrsim 2.9M_{\odot }$; (ii) for the systems of $m_0=2.9–3.0M_{\odot }$ and of mass ratio $\approx 0.8$, the mass of disks which surround the formed black hole is $0.006–0.02M_{\odot }$; (iii) the spin of the formed black hole is $0.78\pm 0.02$ when a black hole is formed after the merger in the dynamical time scale. This value depends weakly on the total mass and mass ratio, and is about 0.1 larger than that of a black hole formed from nonspinning binary black holes; (iv) for the black hole formation case, Fourier spectrum shape of gravitational waves emitted in the merger and ringdown phases has a universal qualitative feature irrespective of the total mass and mass ratio, but quantitatively, the spectrum reflects the parameters of the binary neutron stars.

A “compensated” isocurvature perturbation consists of an overdensity (or underdensity) in the cold dark matter which is completely cancelled out by a corresponding underdensity (or overdensity) in the baryons. Such a configuration may be generated by a curvaton model of inflation if the cold dark matter is created before curvaton decay and the baryon number is created by the curvaton decay (or vice versa). Compensated isocurvature perturbations, at the level producible by the curvaton model, have no observable effect on cosmic microwave background anisotropies or on galaxy surveys. They can be detected through their effect on the distribution of neutral hydrogen between redshifts 30–300 using 21 cm absorption observations. However, to obtain a good signal to noise ratio, very large observing arrays are needed. We estimate that a fast Fourier transform telescope would need a total collecting area of about 20 square kilometers to detect a curvaton generated compensated isocurvature perturbation at more than 5 sigma significance.

We examine the spectrum of inflaton fluctuations resulting from any given long period of exponential inflation. Infrared and ultraviolet divergences in the inflaton dispersion summed over all modes do not appear in our approach. We show how the scale invariance of the perturbation spectrum arises. We also examine the spectrum of scalar perturbations of the metric that is created by the inflaton fluctuations that have left the Hubble sphere during inflation and the spectrum of density perturbations that they produce at reentry after inflation has ended. When the inflaton dispersion spectrum is renormalized during the expansion, we show (for the case of the quadratic inflaton potential) that the density perturbation spectrum approaches a mass-independent limit as the inflaton mass approaches zero, and remains near that limiting value for masses less than about $1/4$ of the inflationary Hubble constant. We show that this limiting behavior does not occur if one only makes the Minkowski space subtraction, without the further adiabatic subtractions that involve time derivatives of the expansion scale factor $a(t)$. We also find a parametrized expression for the energy density produced by the change in $a(t)$ as inflation ends. If the end of inflation were sufficiently abrupt, then the temperature corresponding to this energy density could be very significant. We also show that fluctuations of the inflaton field that are present before inflation starts are not dissipated during inflation and could have a significant observational effect today. The mechanism for this is caused by the initial fluctuations through stimulated emission from the vacuum.