The proton form factors at large momentum transfer are dominated by two contributions which are associated with the hard and soft rescattering, respectively. Motivated by a very active experimental form factor program at intermediate values of momentum transfers, $Q^2\sim 5–15{\mathrm{GeV}}^2$, where an understanding in terms of only a hard rescattering mechanism cannot yet be expected, we investigate in this work the soft rescattering contribution using soft collinear effective theory (SCET). Within such a description, the form factor is characterized, besides the hard scale $Q^2$, by a hard-collinear scale $Q\Lambda$, which arises due to the presence of soft spectators, with virtuality ${\Lambda }^2$ ($\Lambda \sim 0.5\mathrm{GeV}$), such that $Q^2\gg Q\Lambda \gg {\Lambda }^2$. We show that in this case a two-step factorization can be successfully carried out using the SCET approach. In a first step (${\mathrm{SCET}}_I$), we perform the leading-order matching of the QCD electromagnetic current onto the relevant ${\mathrm{SCET}}_I$ operators and perform a resummation of large logarithms using renormalization group equations. We then discuss the further matching onto a ${\mathrm{SCET}}_{II}$ framework, and propose the factorization formula (accurate to leading logarithmic approximation) for the Dirac form factor, accounting for both hard and soft contributions. We also present a qualitative discussion of the phenomenological consequences of this new framework.

We present the first measurement of the color representation of the hadronically decaying $W$ boson in $t\overline{t}$ events, from $5.3{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, “jet pull,” is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored $W$ bosons is $0.56\pm 0.42(\mathrm{stat}+\mathrm{syst})$, in agreement with the standard model.

In this work we present a class of traveling solitons in Lorentz and $CPT$ breaking systems. In the case of Lorentz violating scenarios, as far as we know, only static solitonic configurations were analyzed up to now in the literature. Here it is shown that it is possible to construct some traveling solitons which cannot be mapped into static configurations by means of Lorentz boosts due to explicit breaking. In fact, the traveling solutions cannot be reached from the static ones by using something similar to a Lorentz boost in those cases. Furthermore, in the model studied, a complete set of exact solutions is obtained. The solutions present a critical behavior controlled by the choice of an arbitrary integration constant.

We propose to use a model-independent criterion based on first integrals of motion, due to Noether symmetries of the equations of motion, in order to classify the dark energy models in the context of scalar field (quintessence or phantom) Friedmann-Lemaître-Robertson-Walker cosmologies. In general, the Noether symmetries play an important role in physics because they can be used to simplify a given system of differential equations as well as to determine the integrability of the system. The Noether symmetries are computed for nine distinct accelerating cosmological scenarios that contain a homogeneous scalar field associated with different types of potentials. We verify that all the scalar field potentials, presented here, admit the trivial first integral, namely, energy conservation, as they should. We also find that the exponential potential inspired from scalar field cosmology, as well as some types of hyperbolic potentials, include extra Noether symmetries. This feature suggests that these potentials should be preferred along the hierarchy of scalar field potentials. Finally, using the latter potentials, in the framework of either quintessence or phantom scalar field cosmologies that contain also a nonrelativistic matter (dark matter) component, we find that the main cosmological functions, such as the scale factor of the Universe, the scalar field, the Hubble expansion rate, and the metric of the Friedmann-Lemaître-Robertson-Walker space-time, are computed analytically. Interestingly, under specific circumstances the predictions of the exponential and hyperbolic scalar field models are equivalent to those of the $\Lambda \mathrm{CDM}$ model, as far as the global dynamics and the evolution of the scalar field are concerned. The present analysis suggests that our technique appears to be very competitive to other independent tests used to probe the functional form of a given potential and thus the associated nature of dark energy.

In this paper, we investigate possible solutions to the coincidence problem in flat phantom dark-energy models with a constant dark-energy equation of state and quintessence models with a linear scalar field potential. These models are representative of a broader class of cosmological scenarios in which the universe has a finite lifetime. We show that, in the absence of anthropic constraints, including a prior probability for the models inversely proportional to the total lifetime of the universe excludes models very close to the $\Lambda$ cold dark matter model. This relates a cosmological solution to the coincidence problem with a dynamical dark-energy component having an equation-of-state parameter not too close to $-1$ at the present time. We further show that anthropic constraints, if they are sufficiently stringent, may solve the coincidence problem without the need for dynamical dark energy.

Motivated by the recent low-threshold measurements of the solar ${}^8\mathrm{B}$ neutrino spectrum performed by Borexino, Super-Kamiokande and the Sudbury Neutrino Observatory—all now monitoring the transition regime between low-energy (vacuumlike) and high-energy (matter-dominated) flavor conversions—we consider the role of subdominant dynamical terms induced by new flavor-changing interactions. We find that the presence of such perturbations with strength $\sim {10}^{-1}{G}_F$ is now favored, offering a better description of the anomalous behavior suggested by the new results, whose spectrum shows no sign of the typical low-energy upturn predicted by the standard Mikheyev-Smirnov-Wolfenstein (MSW) mechanism. Our findings, if interpreted in a 2-flavor scheme, provide a hint of such new interactions at the $\sim 2\sigma$ level, which is rather robust with respect to 3-flavor effects possibly induced by nonzero ${\theta }_{13}$.

We present results for one-loop matching factors of four-fermion operators composed of HYP-smeared staggered fermions. We generalize previous calculations by using the tree-level improved Symanzik gauge action. These results are needed for our companion numerical calculation of $B_K$ and related matrix elements. We find that the impact on one-loop matching factors of using the improved gluon action is much smaller than that from the use of either HYP-smearing or mean-field improvement. The one-loop coefficients for mean-field improved, HYP-smeared operators with the Symanzik gauge action have a maximum magnitude of $O(1)\times {\alpha }_s$, indicating that perturbation theory is reasonably convergent.

We show how gauge coupling unification is successfully implemented through nonsupersymmetric grand unified theory, $SO(10)\times G_f(G_f=S_4,SO(3{)}_f,SU(3{)}_f)$, using a low-scale flavor-symmetric model of the type $SU(2{)}_L\times U(1{)}_Y\times SU(3{)}_C\times S_4$ recently proposed by Hagedorn, Lindner, and Mohapatra, while assigning matter-parity discrete symmetry for the dark matter stability. For gauge coupling unification in the single-step–breaking case, we show that a color-octet fermion and a hyperchargeless weak triplet fermionic dark matter are the missing particles needed to complete its minimal supersymmetric standard model-equivalent degrees of freedom. When these are included, the model automatically predicts the nonsupersymmetric grand unification with a scale identical to the minimal supersymmetric standard model/grand unified theory scale. We also find a two-step–breaking model with Pati-Salam intermediate symmetry where the dark matter and a low-mass color-octet scalar or the fermion are signaled by grand unification. The proton-lifetime predictions are found to be accessible to ongoing or planned searches in a number of models. We discuss the grand unified origin of the light fermionic triplet dark matter, the color-octet fermion, and their phenomenology.

The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of ${\mathcal{M}}_{D-1}\times S^1$, where $D$ is the spacetime dimension and ${\mathcal{M}}_{D-1}$ stands for a conformal Minkowski spacetime in $D-1$ dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.

The post Newtonian parameter is considered in the chameleon-Brans-Dicke model. In the first step, the general form of this parameter and also effective gravitational constant is obtained. An arbitrary function for $f(\Phi )$, which indicates the coupling between matter and scalar field, is introduced to investigate validity of solar system constraint. It is shown that the chameleon-Brans-Dicke model can satisfy the solar system constraint and gives us an $\omega$ parameter of order ${10}^4$, which is in comparable to the constraint which has been indicated in [19].

We present numerical simulations of a rotating black hole distorted by a pulse of ingoing gravitational radiation. For strong pulses, we find up to five concentric marginally outer trapped surfaces. These trapped surfaces appear and disappear in pairs, so that the total number of such surfaces at any given time is odd. The world tubes traced out by the marginally outer trapped surfaces are found to be spacelike during the highly dynamical regime, approaching a null hypersurface at early and late times. We analyze the structure of these marginally trapped tubes in the context of the dynamical horizon formalism, computing the expansion of outgoing and incoming null geodesics, as well as evaluating the dynamical horizon flux law and the angular momentum flux law. Finally, we compute the event horizon. The event horizon is well-behaved and approaches the apparent horizon before and after the highly dynamical regime. No new generators enter the event horizon during the simulation.

In this work we study the cosmology of the general $f(T)$ gravity theory. We express the modified Einstein equations using covariant quantities, and derive the gauge-invariant perturbation equations in covariant form. We consider a specific choice of $f(T)$, designed to explain the observed late-time accelerating cosmic expansion without including an exotic dark energy component. Our numerical solution shows that the extra degree of freedom of such $f(T)$ gravity models generally decays as one goes to smaller scales, and consequently its effects on scales such as galaxies and galaxies clusters are small. But on large scales, this degree of freedom can produce large deviations from the standard $\Lambda \mathrm{CDM}$ scenario, leading to severe constraints on the $f(T)$ gravity models as an explanation to the cosmic acceleration.

We investigate non-Gaussianity in general single field models without assuming slow-roll conditions or the exact scale invariance of the scalar power spectrum. The models considered include general single field inflation (e.g. Dirac-Born-Infeld and canonical inflation) as well as bimetric models. We compute the full non-Gaussian amplitude $\mathcal{A}$, its size $f_{\mathrm{NL}}$, its shape, and the running with scale $n_{\mathrm{NG}}$. In doing so we show that observational constraints allow significant violations of slow-roll conditions and we derive explicit bounds on slow-roll parameters for fast-roll single field scenarios. A variety of new observational signatures is found for models respecting these bounds. We also explicitly construct concrete model implementations giving rise to this new phenomenology.

Whereas preheating after chaotic and hybrid inflation models has been abundantly studied in the literature, preheating in small field inflation models, where the curvature of the inflaton potential is negative during inflation, remains less explored. In these models, a tachyonic instability at the end of inflation leads to a succession of exponentially large increases and decreases of the inflaton fluctuations as the inflaton condensate oscillates around the minimum of its potential. The net effect is a competition between low-momentum modes which grow and decrease significantly, and modes with higher momenta which grow less but also decrease less. We develop an analytical description of this process, which is analogous to the quantum mechanical problem of tunneling through a volcano-shaped potential. Depending on the parameters, preheating may be so efficient that it completes in less than one oscillation of the inflaton condensate. Preheating after small field inflation may also be followed by a long matter-dominated stage before the Universe thermalizes, depending on the energy scale of inflation and the details of the inflaton interactions. Finally, another feature of these models is that the spectrum of the inflaton fluctuations at the end of preheating may be peaked around the Hubble scale. In fact, because preheating starts when the second slow-roll parameter $|\eta |$ becomes of order unity while the first slow-roll parameter $ϵ$ is still much smaller than 1, the Universe is still inflating during preheating and the modes amplified by the initial tachyonic instability leave the Hubble radius. This may lead to an abundant production of primordial black holes and gravitational waves with frequencies today which are naturally small enough to fall into the range accessible by high-sensitivity interferometric experiments.

We present results on the nucleon electromagnetic form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length $L=2.1\mathrm{fm}$ and $L=2.8\mathrm{fm}$. Cutoff effects are investigated using three different values of the lattice spacings, namely $a=0.089\mathrm{fm}$, $a=0.070\mathrm{fm}$ and $a=0.056\mathrm{fm}$. The nucleon magnetic moment, Dirac and Pauli radii are obtained in the continuum limit and chirally extrapolated to the physical pion mass allowing for a comparison with experiment.

The null search for the Higgs boson at the Tevatron implies strong constraints on heavy colored particles that increase the gluon-fusion induced production rate of the Higgs. We investigate the implications of the Tevatron exclusion limit on example extensions of the standard model that contain a new scalar state transforming as either an adjoint or a fundamental under the QCD gauge group. The bounds on the adjoint (fundamental) scalar mass exceed 200 GeV (100 GeV) for natural choices of scalar-sector parameters.

A scalar field model with nonminimal derivative coupling to gravity is considered. It is shown that although in the absence of matter and potential the phantom divide line crossing is forbidden, for the power law potential and in the presence of matter this crossing is, in principle, possible.

In this paper we study the dynamical instability of Sakai-Sugimoto’s holographic QCD model at finite baryon density. In this model, the baryon density, represented by the smeared instanton on the world volume of the probe $D8$-$\overline{D8}$ mesonic brane, sources the world-volume electric field, and through the Chern-Simons term it will induce the instability to form a chiral helical wave at sufficient high density. Our results show that this kind of instability occurs for sufficiently high baryon number densities. The phase diagram of holographic QCD will thus be changed from the one which is based only on thermodynamics.

In nonlinear electrodynamics, by implementing the causality principle as the requirement that the group velocity of elementary excitations over a background field should not exceed the speed of light in the vacuum $c=1$, and the unitarity principle as the requirement that the residue of the propagator should be nonnegative, we establish the positive convexity of the effective Lagrangian on the class of constant fields, also the positivity of all characteristic dielectric and magnetic permittivity constants that are derivatives of the effective Lagrangian with respect to the field invariants. Violation of the general principles by the one-loop approximation in QED at exponentially large magnetic field is analyzed, resulting in complex energy ghosts that signal the instability of the magnetized vacuum. Superluminal excitations (tachyons) appear, too, but for the magnetic field exceeding its instability threshold. Also other popular Lagrangians are tested to establish that the ones leading to spontaneous vacuum magnetization possess wrong convexity.