The $CPT$-even gauge sector of the standard model extension is composed of 19 components comprised in the tensor $(K_F{)}_{\mu \nu \rho \sigma }$, of which nine do not yield birefringence. In this work, we examine the Maxwell electrodynamics supplemented by these nine nonbirefringent $CPT$-even components in aspects related to the Feynman propagator and full consistency (stability, causality, unitarity). We adopt a prescription that parametrizes the nonbirefringent components in terms of a symmetric and traceless tensor, $K_{\mu \nu }$, and second parametrization that writes $K_{\mu \nu }$ in terms of two arbitrary four-vectors, $U_{\mu }$ and $V_{\nu }$. We then explicitly evaluate the gauge propagator of this electrodynamics in a tensor closed way. In the sequel, we show that this propagator and involved dispersion relations can be specialized for the parity-odd and parity-even sectors of the tensor $(K_F{)}_{\mu \nu \rho \sigma }$. In this way, we reassess some results of the literature and derive some new outcomes showing that the parity-even anisotropic sector engenders a stable, noncausal and unitary electrodynamics.

We present gravitational waveforms for the last orbits and merger of black-hole-binary systems along two branches of the black-hole-binary parameter space: equal-mass binaries with equal nonprecessing spins, and nonspinning unequal-mass binaries. The waveforms are calculated from numerical solutions of Einstein’s equations for black-hole binaries that complete between six and ten orbits before merger. Along the equal-mass spinning branch, the spin parameter of each black hole is ${\chi }_i=S_i/M_i^2\in [-0.85,0.85]$, and along the unequal-mass branch the mass ratio is $q=M_2/M_1\in [1,4]$. We discuss the construction of low-eccentricity puncture initial data for these cases, the properties of the final merged black hole, and compare the last 8–10 gravitational-wave cycles up to $M\omega =0.1$ with the phase and amplitude predicted by standard post-Newtonian (PN) approximants. As in previous studies, we find that the phase from the 3.5PN TaylorT4 approximant is most accurate for nonspinning binaries. For equal-mass spinning binaries the 3.5PN TaylorT1 approximant (including spin terms up to only 2.5PN order) gives the most robust performance, but it is possible to treat TaylorT4 in such a way that it gives the best accuracy for spins ${\chi }_i>-0.75$. When high-order amplitude corrections are included, the PN amplitude of the $(\ell =2,m=\pm 2)$ modes is larger than the numerical relativity amplitude by between 2–4%.

A systematic study of gravitational waves from galaxy mergers, through $N$-body simulations, was performed. In particular, we investigated the relative importance of galaxy components (disk, bulge and halo) and effects of initial relative velocity, relative angular momentum and mass ratio of the galaxies. We found that the features of light curve of gravitational waves, such as peak width and luminosity, are reliably simulated with particle numbers larger than $\sim {10}^4$. Dominant contribution to gravitational wave emission came from the halo component, while peak luminosity amounted to ${10}^{31}\mathrm{erg}/\sec$ for the collision of two halos with mass $3.8\times {10}^{12}{h}^{-1}{M}_{\odot }$. We also found that the initial relative velocity in the direction of the initial separation did not significantly affect gravitational wave emission, while the initial relative angular momentum broadened the peak width and suppressed the luminosity. Mass dependence of the peak luminosity was also investigated, and we obtained evidence that the luminosity is proportional to the cubic mass when the scaling relation is satisfied. This behavior was considered by a simple analysis.

We address the infrared (IR) divergence problem during inflation that appears in the loop corrections to the primordial perturbations. In our previous paper, we claimed that, at least in single field models, the IR divergence is originating from the gauge artifact. Namely, diverging IR corrections should not appear in genuine gauge-invariant observables. We propose here one simple but explicit example of such gauge-invariant quantities. Then, we explicitly calculate such a quantity to find that the IR divergence is absent at the leading order in the slow-roll approximation for the usual scale-invariant vacuum state. At the same time we notice that there is a subtle issue on the gauge invariance in how to specify the initial vacuum state.

The phase structure of two-flavor QCD is explored for thermal systems with finite baryon- and isospin-chemical potentials, ${\mu }_{\mathrm{B}}$ and ${\mu }_{\mathrm{iso}}$, by using the Polyakov-loop extended Nambu–Jona-Lasinio (PNJL) model. The PNJL model with the scalar-type eight-quark interaction can reproduce lattice QCD data at not only ${\mu }_{\mathrm{iso}}={\mu }_{\mathrm{B}}=0$, but also ${\mu }_{\mathrm{iso}}>0$ and ${\mu }_{\mathrm{B}}=0$. In the ${\mu }_{\mathrm{iso}}$-${\mu }_{\mathrm{B}}$-$T$ space, where $T$ is temperature, the critical endpoint of the chiral phase transition in the ${\mu }_{\mathrm{B}}$-$T$ plane at ${\mu }_{\mathrm{iso}}=0$ moves to the tricritical point of the pion-superfluidity phase transition in the ${\mu }_{\mathrm{iso}}$-$T$ plane at ${\mu }_{\mathrm{B}}=0$ as ${\mu }_{\mathrm{iso}}$ increases. The thermodynamics at small $T$ is controlled by $\sqrt{{\sigma }^2+{\pi }^2}$ defined by the chiral and pion condensates, $\sigma$ and $\pi$.

Constraints from analyticity are combined with experimental electron-proton scattering data to determine the proton charge radius. In contrast to previous determinations, we provide a systematic procedure for analyzing arbitrary data without model-dependent assumptions on the form-factor shape. We also investigate the impact of including electron-neutron scattering data, and $\pi \pi \to N\overline{N}$ data. Using representative data sets we find $r_E^p=0.870\pm 0.023\pm 0.012\mathrm{fm}$ using just proton scattering data; $r_E^p={0.880}_{-0.020}^{+0.017}\pm 0.007\mathrm{fm}$ adding neutron data; and $r_E^p=0.871\pm 0.009\pm 0.002\pm 0.002\mathrm{fm}$ adding $\pi \pi$ data. The analysis can be readily extended to other nucleon form factors and derived observables.

In a previous paper [S. Nakamura, H. Ooguri, and C. S. Park, Phys. Rev. D 81, 044018 (2010)], we showed that the Reissner-Nordström black hole in the five-dimensional anti–de Sitter space coupled to the Maxwell theory with the Chern-Simons term is unstable when the Chern-Simons coupling is sufficiently large. In the dual conformal field theory, the instability suggests a spatially modulated phase transition. In this paper, we construct and analyze nonlinear solutions which describe the endpoint of this phase transition. In the limit where the Chern-Simons coupling is large, we find that the phase transition is of the second order with the mean field critical exponent. However, the dispersion relation with the Van Hove singularity enhances quantum corrections in the bulk, and we argue that this changes the order of the phase transition from the second to the first. We compute linear response functions in the nonlinear solution and find an infinite off-diagonal DC conductivity in the new phase.

We point out that there is a non-Abelian instability for a non-Abelian plasma which does not allow both for a net nonzero color charge and the existence of field configurations which are coherent over a volume $v$ whose size is determined by the chemical potential. The basic process which leads to this result is the Schwinger decay of chromoelectric fields, for the case where the field arises from commutators of constant potentials, rather than as the curl of spacetime dependent potentials. The case where instability is obtained can be expressed in terms of fields (with constant potentials) as $F^{a\mu \nu }{F}_{\mu \nu }^a<0$, $A^{a\mu }{A}_{\mu }^a<0$.

In chameleon dark energy models, local gravity constraints tend to rule out parameters in which observable cosmological signatures can be found. We study viable chameleon potentials consistent with a number of recent observational and experimental bounds. A novel chameleon field potential, motivated by $f(R)$ gravity, is constructed where observable cosmological signatures are present both at the background evolution and in the growth rate of the perturbations. We study the evolution of matter density perturbations on low redshifts for this potential and show that the growth index today ${\gamma }_0$ can have significant dispersion on scales relevant for large scale structures. The values of ${\gamma }_0$ can be even smaller than 0.2 with large variations of $\gamma$ on very low redshifts for the model parameters constrained by local gravity tests. This gives a possibility to clearly distinguish these chameleon models from the $\Lambda$-cold-dark-matter ($\Lambda \mathrm{CDM}$) model in future high-precision observations.

We compare Newtonian and general relativistic descriptions of the stationary accretion of self-gravitating fluids onto compact bodies. Spherical symmetry and thin gas approximation are assumed. Luminosity depends, among other factors, on the temperature and the contribution of gas to the total mass, in both—general relativistic $(L_{\mathrm{GR}})$ and Newtonian $(L_N)$—models. We discover a remarkable universal behavior for transonic flows: the ratio of respective luminosities $L_{\mathrm{GR}}/L_N$ is independent of the fractional mass of the gas and depends on asymptotic temperature. It is close to 1 in the regime of low asymptotic temperatures and can grow several times at high temperatures. These conclusions are valid for a wide range of polytropic equations of state.

In this paper, we study the recent excess of low-energy events observed by the CoGeNT Collaboration and the annual modulation reported by the DAMA/LIBRA Collaboration, and discuss whether these signals could both be the result of the same elastically scattering dark matter particle. We find that, without channeling but when taking into account uncertainties in the relevant quenching factors, a dark matter candidate with a mass of approximately $7\mathrm{GeV}$ and a cross section with nucleons of ${\sigma }_{\mathrm{DM}-\mathrm{N}}\sim 2\times {10}^{-4}\mathrm{pb}$ ($2\times {10}^{-40}{\mathrm{cm}}^2$) could account for both of these observations. We also comment on the events recently observed in the oxygen band of the CRESST experiment and point out that these could potentially be explained by such a particle. Lastly, we compare the region of parameter space favored by DAMA/LIBRA and CoGeNT to the constraints from XENON10, XENON100, and CDMS (Si) and find that these experiments cannot at this time rule out a dark matter interpretation of these signals.

The misalignment mechanism for axion production depends on the temperature-dependent axion mass. The latter has recently been determined within the interacting instanton liquid model, and provides for the first time a well-motivated axion mass for all temperatures. We reexamine the constraints placed on the axion parameter space in the light of this new mass function. Taking this mass at face value, we find an accurate and updated constraint $f_a\le 2.8(\pm 2)\times {10}^{11}\mathrm{GeV}$ or $m_a\ge 21(\pm 2)\mu \mathrm{eV}$ from the misalignment mechanism in the classic axion window (thermal scenario). However, this is superseded by axion string radiation which leads to $f_a\lesssim {3.2}_{-2}^{+4}\times {10}^{10}\mathrm{GeV}$ or $m_a\gtrsim {0.20}_{-0.1}^{+0.2}\mathrm{meV}$. In this analysis, we take care to precisely compute the effective degrees of freedom and, to fill a gap in the literature, we present accurate fitting formulas. We solve the evolution equations exactly, and find that analytic results used to date generally underestimate the full numerical solution by a factor 2–3. In the inflationary scenario, axions induce isocurvature fluctuations and constrain the allowed inflationary scale $H_I$. Taking anharmonic effects into account, we show that these bounds are actually weaker than previously computed. Considering the fine-tuning issue of the misalignment angle in the whole of the anthropic window, we derive new bounds which open up the inflationary window near ${\theta }_a\to \pi$. In particular, we find that inflationary dark matter axions can have masses as high as $0.01–1\mathrm{meV}$, covering the whole thermal axion range, with values of $H_I$ up to ${10}^9\mathrm{GeV}$. Quantum fluctuations during inflation exclude dominant dark matter axions with masses above $m_a\lesssim 1\mathrm{meV}$.

The nature of the dark matter remains a mystery. The possibility of an unstable dark matter particle decaying to invisible daughter particles has been explored many times in the past few decades. Meanwhile, weak gravitational lensing shear has gained a lot of attention as a probe of dark energy, though it was previously considered a dark matter probe. Weak lensing is a useful tool for constraining the stability of the dark matter. In the coming decade a number of large galaxy imaging surveys will be undertaken and will measure the statistics of cosmological weak lensing with unprecedented precision. Weak lensing statistics are sensitive to unstable dark matter in at least two ways. Dark matter decays alter the matter power spectrum and change the angular diameter distance-redshift relation. We show how measurements of weak lensing shear correlations may provide the most restrictive, model-independent constraints on the lifetime of unstable dark matter. Our results rely on assumptions regarding nonlinear evolution of density fluctuations in scenarios of unstable dark matter and one of our aims is to stimulate interest in theoretical work on nonlinear structure growth in unstable dark matter models.

We consider a Chaplygin gas model with an exponential potential in framework of braneworld inflation. We apply the slow-roll approximation in the high-energy limit to derive various inflationary spectrum perturbation parameters. We show that the inflation observables depend only on the $e$-folding number $N$ and the final value of the slow-roll parameter ${\epsilon }_{\mathrm{end}}$. Whereas for small running of the scalar spectral index $\frac{d{n}_s}{d\ln k}$, the inflation observables are in good agreement with recent WMAP7 data.

We analytically and numerically show that through the cycles with nonsingular bounce, the amplitude of curvature perturbation on a large scale will be amplified and the power spectrum will redden. In some sense, this amplification will eventually destroy the homogeneity of the background, which will lead to the ultimate end of cycles of the global universe. We argue that for the model with increasing cycles, it might be possible that a fissiparous multiverse will emerge after one or several cycles, in which the cycles will continue only at corresponding local regions.

We propose a new motivation for the stability of dark matter (DM). We suggest that the same non-Abelian discrete flavor symmetry which accounts for the observed pattern of neutrino oscillations, spontaneously breaks to a $Z_2$ subgroup which renders DM stable. The simplest scheme leads to a scalar doublet DM potentially detectable in nuclear recoil experiments, inverse neutrino mass hierarchy, hence a neutrinoless double beta decay rate accessible to upcoming searches, while ${\theta }_{13}=0$ gives no $CP$ violation in neutrino oscillations.

We discuss the possibility of obtaining stronger constraints on non-Newtonian gravity from measuring the gradient of the Casimir force between a cylinder and a plate. The exact analytical expression for the Yukawa-type force in a cylinder-plate configuration is obtained, as well as its asymptotic expansions. The gravitational force is compared with the Casimir force acting between a cylinder and a plate. Numerical computations for the prospective constraints on non-Newtonian gravity are performed for a recently proposed experiment using a microfabricated cylinder attached to a micromachined oscillator. Specifically, it is shown that this experiment is expected to obtain up to 70 times stronger constraints on the Yukawa-type force, compared with the best present day limits, over a wide interaction range from 12.5 to 630 nm.

An extension of the standard model by at least one extra $U(1)$ gauge symmetry has been investigated by many authors. In this paper we explore the possibility that this extra $U(1)$ is anomalous. One possible signature of this model could be given by the photons produced in the decays of the next to lightest supersymmetric particle into the lightest supersymmetric particle.

We consider different patterns of supersymmetry breaking gaugino mass parameters, and implications of these patterns for the phenomenology of neutralinos and charginos in models of low-energy supersymmetry. We outline a general procedure for obtaining approximate values for the neutralino masses relevant for our analysis, and describe the constraints on the gaugino mass parameters which follow from the present experimental limits on the mass of the lightest chargino. We evaluate an upper bound on the mass of the lightest neutralino that follows from the structure of the mass matrix in the studied patterns. Using the experimental lower limit for the chargino mass, we examine the lower bound for the neutralino masses. Using a sum rule for the squared masses of charginos and neutralinos, we discuss how to distinguish between different models for the supersymmetry breaking. We discuss in detail the decay modes of neutralinos and charginos. Our analysis shows that by measuring the masses and decay properties of the neutralinos, one can distinguish between different patterns of supersymmetry breaking in the gaugino sector. We then compare the dark matter characteristics that arise in different models for the supersymmetry breaking gaugino mass parameters.

It is shown that free lattice fermions defined by overlap Dirac operator fulfill the Osterwalder-Schrader reflection positivity condition with respect to the link-reflection. The proof holds true in nongauge models with interactions such as chiral Yukawa models.