The all-flavor solar neutrino flux measured by the Sudbury Neutrino Observatory constrains nonstandard energy losses to less than about 10% of the Sun’s photon luminosity, superseding a helioseismological argument and providing new limits on the interaction strength of low-mass particles. For the axion-photon coupling strength we find $g_{a\gamma }<7\times {10}^{-10}{\mathrm{GeV}}^{-1}$. We also derive explicit limits on the Yukawa coupling to electrons of pseudoscalar, scalar, and vector bosons with keV-scale masses.

The deconfined quantum critical point of a two-dimensional $SU(N)$ antiferromagnet is governed by an Abelian Higgs model in $d=2+1$ spacetime dimensions featuring $N$ complex scalar fields. In this context, we derive for $2\le d\le 4$ an exact formula for the central charge of the $U(1)$ current in terms of the gauge coupling at quantum criticality and compare it with the corresponding result obtained using gauge-gravity duality. There is a remarkable similarity precisely for $d=2+1$. In this case the amplitude of the current correlation function has the same form as predicted by the gauge-gravity duality. We also compare finite temperature results for the charge susceptibility in the large $N$ limit with the result predicted by the gauge-gravity duality. Our results suggest that condensed matter systems at quantum criticality may provide interesting quantitative tests of the gauge-gravity duality even in the absence of supersymmetry.

We analyze the effect of the Pauli-Fierz mass term on a recently established, new massive gravity theory in three space-time dimensions. We show that the Pauli-Fierz mass term makes the new massive gravity theory nonunitary. Moreover, although we add the gravitational Chern-Simons term to this model, the situation remains unchanged and the theory stays nonunitary despite that the structure of the graviton propagator is greatly changed. Thus, the Pauli-Fierz mass term is not allowed to coexist with mass-generating higher-derivative terms in the new massive gravity.

General very special relativity (GVSR) is the curved space-time of very special relativity (VSR) proposed by Cohen and Glashow. The geometry of general very special relativity possesses a line element of Finsler geometry introduced by Bogoslovsky. We calculate the Einstein field equations and derive a modified Friedmann-Robertson-Walker cosmology for an osculating Riemannian space. The Friedmann equation of motion leads to an explanation of the cosmological acceleration in terms of an alternative non-Lorentz invariant theory. A first order approach for a primordial-spurionic vector field introduced into the metric gives back an estimation of the energy evolution and inflation.

In this work, we consider the cosmological constraints on the holographic Ricci dark energy proposed by Gao et al. [Phys. Rev. D 79, 043511 (2009)], by using the observational data currently available. The main characteristic of holographic Ricci dark energy is governed by a positive numerical parameter $\alpha$ in the model. When $\alpha <1/2$, the holographic Ricci dark energy will exhibit a quintomlike behavior; i.e., its equation of state will evolve across the cosmological-constant boundary $w=-1$. The parameter $\alpha$ can be determined only by observations. Thus, in order to characterize the evolving feature of dark energy and to predict the fate of the Universe, it is of extraordinary importance to constrain the parameter $\alpha$ by using the observational data. In this paper, we derive constraints on the holographic Ricci dark energy model from the latest observational data including the Union sample of 307 type Ia supernovae, the shift parameter of the cosmic microwave background given by the five-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey. The joint analysis gives the best-fit results (with $1\sigma$ uncertainty): $\alpha ={0.359}_{-0.025}^{+0.024}$ and ${\Omega }_{\mathrm{m}0}={0.318}_{-0.024}^{+0.026}$. That is to say, according to the observations, the holographic Ricci dark energy takes on the quintom feature. Finally, in light of the results of the cosmological constraints, we discuss the issue of the scalar-field dark energy reconstruction, based on the scenario of the holographic Ricci vacuum energy.

In models of coupled dark energy, in which a dark energy scalar field couples to other matter components, it is natural to expect a coupling to the inflaton as well. We explore the consequences of such a coupling in the context of single-field slow-roll inflation. Assuming an exponential potential for the quintessence field we show that the coupling to the inflaton causes the quintessence field to be attracted toward the minimum of the effective potential. If the coupling is large enough, the field is heavy and is located at the minimum. We show how this affects the expansion rate and the slow-roll of the inflaton field, and therefore the primordial perturbations generated during inflation. We further show that the coupling has an important impact on the processes of reheating and preheating.

We examine dark-energy models in which a quintessence or a phantom field, $\varphi$, rolls near the vicinity of a local minimum or maximum, respectively, of its potential $V(\varphi )$. Under the approximation that $(1/V)(dV/d\varphi )\ll 1$, [although $(1/V)(d^{2}V/d{\varphi }^2)$ can be large], we derive a general expression for the equation-of-state parameter $w$ as a function of the scale factor for these models. The dynamics of the field depends on the value of $(1/V)(d^{2}V/d{\varphi }^2)$ near the extremum, which describes the potential curvature. For quintessence models, when $(1/V)(d^{2}V/d{\varphi }^2)<3/4$ at the potential minimum, the equation-of-state parameter $w(a)$ evolves monotonically, while for $(1/V)(d^{2}V/d{\varphi }^2)>3/4$, $w(a)$ has oscillatory behavior. For phantom fields, the dividing line between these two types of behavior is at $(1/V)(d^{2}V/d{\varphi }^2)=-3/4$. Our analytical expressions agree within 1% with the exact (numerically derived) behavior, for all of the particular cases examined, for both quintessence and phantom fields. We present observational constraints on these models.

The recent Pierre Auger Observatory result suggesting a coincidence of extensive air showers arrival directions with “nearby” active galactic nuclei and HiRes discovery of the Greisen-Zatsepin-Kuzmin cutoff indicates protons to be only or at least the strongly dominant component of primary extra galactic cosmic ray flux. However, showers initiated by these ultrahigh energy particles developed faster than predicted by the simulation calculations with conventional interaction models. This could be evidence of the substantial increase of the $p$-air cross section. The progress in understanding the proton-proton cross section description allows us to examine this possibility, and eventually reject it as an explanation of the ultrahigh energy cosmic ray “pure proton” controversy.

We investigate the behavior of the perturbative relation between the photon energy spectrum in $B\to X_s\gamma$ and the hadronic $P_{+}$ spectrum in semileptonic $B\to X_u\ell \overline{\nu }$ decay at high orders in perturbation theory in the “large-${\beta }_0$” limit, in which only terms of order ${\alpha }_s^n{\beta }_0^{n-1}$ are retained. The leading renormalon in the weight function $W(\Delta ,P_{\gamma })$ relating the two spectra is confirmed to be at $u=1/2$, corresponding to nonperturbative corrections at $O({\Lambda }_{\mathrm{QCD}}/m_b)$. We show that the $P_{\gamma }$ dependent pieces of the weight function have no infrared renormalons in this limit, and so the factorial growth in perturbation theory arises solely from the constant terms. We find no numerical enhancement of leading logarithms, suggesting that fixed-order perturbation theory is more appropriate than a leading-log resummation for the extraction of $|V_{ub}|$. The importance of various terms in the expansion of the weight function is studied using a model for the $B\to X_s\gamma$ photon spectrum. Our analysis suggests that higher order perturbative corrections do not introduce a significant uncertainty in the extraction of $|V_{ub}|$.

We present a grand unified model based on $SO(10)$ with a $\Delta (27)$ family symmetry. Fermion masses and mixings are fitted and agree well with experimental values. An extended seesaw mechanism plays a key role in the generation of the leptonic mixing, which is approximately tribimaximal.

The resummation of soft gluon exchange for QCD hard scattering requires a matrix of anomalous dimensions, which has been computed through two loops. The two-loop matrix is proportional to the one-loop matrix. Recently there have been proposals that this proportionality extends to higher loops. One can test such proposals by computing the dependence of this matrix on the matter content in a generic gauge theory. It is shown that for the matter-dependent part the proportionality extends to three loops for arbitrary massless processes.

We continue the study of heterotic non-Abelian Bogomolny-Prasad-Sommerfield (BPS) saturated flux tubes (strings). Previously, such solutions were obtained in $\mathrm{U}(N)$ gauge theories: $\mathcal{N}=2$ supersymmetric QCD deformed by superpotential terms $\mu {\mathcal{A}}^2$ breaking $\mathcal{N}=2$ supersymmetry down to $\mathcal{N}=1$. In these models one cannot consider the limit $\mu \to \infty$ which would eliminate adjoint fields: the bulk theory develops a Higgs branch; the emergence of massless particles in the bulk precludes one from taking the limit $\mu \to \infty$. This drawback is absent in the $M$ model [A. Gorsky, M. Shifman, and A. Yung, Phys. Rev. D 75, 065032 (2007)] where the matter sector includes additional “meson” fields $M$ introduced in a special way. We generalize our previous results to the $M$ model, derive the heterotic string [the string world-sheet theory is a heterotic $\mathcal{N}=(0,2)$ sigma model, with the $CP(N-1)$ target space for bosonic fields and an extra right-handed fermion coupled to the fermion fields of the $\mathcal{N}=(2,2)$ $CP(N-1)$ model], and then explicitly obtain all relevant zero modes. This allows us to relate parameters of the microscopic $M$ model to those of the world-sheet theory. The limit $\mu \to \infty$ is perfectly smooth. Thus, the full-blown and fully analyzed heterotic string emerges, for the first time, in the $\mathcal{N}=1$ theory with no adjoint fields. The fate of the confined monopoles is discussed.

In this paper we investigate the nature of the transition from Abelian to non-Abelian confinement (i.e. crossover vs phase transition). To this end we consider the basic $\mathcal{N}=2$ model where non-Abelian flux tubes (strings) were first found: supersymmetric QCD with the $\mathrm{U}(N)$ gauge group and $N_f=N$ flavors of fundamental matter (quarks). The Fayet-Iliopoulos term $\xi$ triggers the squark condensation and leads to the formation of non-Abelian strings. There are two adjustable parameters in this model: $\xi$ and the quark mass difference $\Delta m$. We obtain the phase diagram on the $(\xi ,\Delta m)$ plane. At large $\xi$ and small $\Delta m$ the world-sheet dynamics of the string orientational moduli is described by the $\mathcal{N}=2$ two-dimensional $CP(N-1)$ model. We show that as we reduce $\xi$ the theory exhibits a crossover to the Abelian (Seiberg-Witten) regime. Instead of $N^2$ degrees of freedom of non-Abelian theory, now only $N$ degrees of freedom survive in the low-energy spectrum. Dyons with certain quantum numbers condense, leading to the formation of the Abelian $Z_N$ strings whose fluxes are fixed inside the Cartan subalgebra of the gauge group. As we increase $N$ this crossover grows exceedingly sharper, becoming a genuine phase transition at $N=\infty$.

We analyze the conceptual role of background independence in the application of the effective average action to quantum gravity. Insisting on a background independent renormalization group (RG) flow the coarse graining operation must be defined in terms of an unspecified variable metric since no rigid metric of a fixed background spacetime is available. This leads to an extra field dependence in the functional RG equation and a significantly different RG flow in comparison to the standard flow equation with a rigid metric in the mode cutoff. The background independent RG flow can possess a non-Gaussian fixed point, for instance, even though the corresponding standard one does not. We demonstrate the importance of this universal, essentially kinematical effect by computing the RG flow of quantum Einstein gravity in the “conformally reduced” Einstein-Hilbert approximation which discards all degrees of freedom contained in the metric except the conformal one. Without the extra field dependence the resulting RG flow is that of a simple ${\varphi }^4$ theory. By including it one obtains a flow with exactly the same qualitative properties as in the full Einstein-Hilbert truncation. In particular it possesses the non-Gaussian fixed point which is necessary for asymptotic safety.

A new classical solution for the Yang-Mills theory in which the Euclidean energy plays a role of a parameter is discussed. The instanton and sphaleron are shown to be particular examples of this more general solution. The energy parameter for them takes on special values, which are zero and sphaleron mass for the instanton and sphaleron, respectively. The solution is employed to describe the tunneling process, which is accompanied by a variation of the topological charge. A range of temperatures, where the new solution makes this tunneling more effective than the known mechanisms based on the instanton, caloron, or sphaleron is found.

Recently, in the context of $f(R)$ modified theories of gravity, a new type of model has been proposed where one directly couples the scalar curvature to matter. As any model in $f(R)$ theory, there are certain conditions which have to be satisfied in order to ensure that the model is viable and physically meaningful. In this paper, one considers this new class of models with curvature-matter coupling and study them from the point of view of the energy conditions and of their stability under the Dolgov-Kawasaki criterion.

We investigate the black hole thermodynamics in a “deformed” relativity framework where the energy-momentum dispersion law is Lorentz-violating and the Schwarzchild-like metric is momentum-dependent with a Planckian cutoff. We obtain net deviations of the basic thermodynamical quantities from the Hawking-Bekenstein predictions: actually, the black hole evaporation is expected to quit at a nonzero critical mass value (of the order of the Planck mass), leaving a zero temperature remnant, and avoiding a spacetime singularity. Quite surprisingly, the present semiclassical corrections to black hole temperature, entropy, and heat capacity turn out to be identical to the ones obtained within some quantum approaches.

Hybrid inflation faces two well-known problems: the blue spectrum of the nonsupersymmetric version of the model and the fine-tuning of the initial conditions of the fields leading to sufficient inflation to account for the standard cosmological problems. They are investigated by studying the exact two-fields dynamics instead of assuming slow-roll. When the field values are restricted to be less than the reduced Planck mass, a non-negligible part of the initial condition space (around 15% depending on potential parameters) leads to successful inflation. Most of it is located outside the usual inflationary valley and organized in continuous patterns instead of being isolated as previously found. Their existence is explained and their properties are studied. This shows that no excessive fine-tuning is required for successful hybrid inflation. Moreover, by extending the initial condition space to Planckian-like or super-Planckian values, inflation becomes generically sufficiently long and can produce a red-tilted scalar power spectrum due to slow-roll violations. The robustness of these properties is confirmed by conducting our analysis on three other models of hybrid-type inflation in various framework: “smooth” and “shifted” inflation in SUSY and SUGRA, and “radion assisted” gauge inflation. A high percentage of successful inflation for smooth hybrid inflation (up to 80%) is observed.

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We calculate quasilinear effects in the growth of structure in $f(R)$ models of gravity using perturbation theory. We find significant deviations in the bispectrum that depend on cosmic time, length scale and triangle shape. However the deviations in the reduced bispectrum $Q$ for $f(R)$ models are at the percent level, much smaller than the deviations in the bispectrum itself. This implies that three-point correlations can be predicted to a good approximation simply by using the modified linear growth factor in the standard gravity formalism. Our results suggest that gravitational clustering in the weakly nonlinear regime is not fundamentally altered, at least for a class of gravity theories that are well described in the Newtonian regime by the parameters $G_{\mathrm{eff}}$ and $\Phi /\Psi$. This approximate universality was also seen in the N-body simulation measurements of the power spectrum by Stabenau & Jain (2006), and in other recent studies based on simulations. Thus predictions for such modified gravity models in the regime relevant to large-scale structure observations may be less daunting than expected on first principles. We discuss the many caveats that apply to such predictions.

Recent observational data of supernovae point to $\Lambda$-dominated flat cosmological models. However, an alternative model in which we happen to live in an underdense region requires no dark energy or modification of gravity. This challenges the Copernican principle. We show that the integrated Sachs-Wolfe (ISW) effect is an excellent discriminator between anti-Copernican inhomogeneous models and the standard Copernican models. As a reference model, we consider an anti-Copernican inhomogeneous model that consists of two inner negatively curved underdense regions and an outer flat Einstein-de Sitter region. We assume that these regions are connected by two thin walls at redshifts $z=0.067$ and $z=0.45$. In the inner two regions, the first-order ISW effect is dominant and comparable to that in the concordant flat-$\Lambda$ models. In the outer Einstein-de Sitter region, the first-order ISW effect vanishes but the second-order ISW effect plays a dominant role, while the first-order ISW effect is dominant in the flat-$\Lambda$ models at moderate redshifts. This difference can discriminate the anti-Copernican models from the concordant flat-$\Lambda$ model. At high redshifts, the second-order ISW effect is dominant both in our inhomogeneous model and in the concordant model. In the outer region, moreover, the ISW effect due to large-scale density perturbations with a present matter density contrast ${ϵ}_{m0}\ll 0.37$ is negligible, while the effect due to small-scale density perturbations (such as clusters of galaxies, superclusters, and voids) with ${ϵ}_{m0}\gg 0.37$ would generate anisotropies which are larger than those generated by the ISW effect in the concordant model.