Adding a fourth generation to the standard model and assuming it to be valid up to some cutoff $\Lambda$, we show that electroweak symmetry is broken by radiative corrections due to the fourth generation. The effects of the fourth generation are isolated using a Lagrangian with a genuine scalar without self-interactions at the classical level. For masses of the fourth generation consistent with electroweak precision data (including the $B\to K\pi$ $CP$ asymmetries), we obtain a Higgs mass of the order of a few hundreds GeV and a cutoff $\Lambda$ around 1–2 TeV. We study the reliability of the perturbative treatment used to obtain these results taking into account the running of the Yukawa couplings of the fourth quark generation with the aid of the renormalization group equations, finding similar allowed values for the Higgs mass but a slightly lower cutoff due to the breaking of the perturbative regime. Such low cutoff means that the effects of new physics needed to describe electroweak interactions at energy above $\Lambda$ should be measurable at the LHC. We use the minimal supersymmetric extension of the standard model with four generations as an explicit example of models realizing the dynamical electroweak symmetry breaking by radiative corrections and containing new physics. Here, the cutoff is replaced by the masses of the squarks and electroweak symmetry breaking by radiative corrections requires the squark masses to be of the order of 1 TeV.

During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. We derive upper limits on the CRE flux from the Sun’s direction, and use these bounds to constrain two classes of dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.

Low energy descriptions of metastable supersymmetry breaking models often possess an accidental $R$ symmetry. Viable phenomenological applications of this class of models require $R$ symmetry to be broken in the ground state. This can be achieved in O’Raifeartaigh-like models where some of the chiral superfields carry negative $R$ charges. In this paper we consider UV completions of this class of models and formulate necessary conditions that they must satisfy. We show that the $R$ symmetry of the IR description can be traced to an anomalous or anomaly-free $R$ symmetry of the UV theory and discuss several representative examples.

We present a concise new definition of Finsler spacetimes that generalizes Lorentzian metric manifolds and provides consistent backgrounds for physics. Extending standard mathematical constructions known from Finsler spaces, we show that geometric objects like the Cartan nonlinear connection and its curvature are well defined almost everywhere on Finsler spacetimes, including their null structure. This allows us to describe the complete causal structure in terms of timelike and null curves; these are essential to model physical observers and the propagation of light. We prove that the timelike directions form an open convex cone with a null boundary, as is the case in Lorentzian geometry. Moreover, we develop action integrals for physical field theories on Finsler spacetimes, and tools to deduce the corresponding equations of motion. These are applied to construct a theory of electrodynamics that confirms the claimed propagation of light along Finsler null geodesics.

Nonthermal dark matter generation is an appealing alternative to the standard paradigm of thermal WIMP dark matter. We reconsider nonthermal production mechanisms in a systematic way, and develop a numerical code for accurate computations of the dark matter relic density. We discuss, in particular, scenarios with long-lived massive states decaying into dark matter particles, appearing naturally in several beyond the standard model theories, such as supergravity and superstring frameworks. Since nonthermal production favors dark matter candidates with large pair annihilation rates, we analyze the possible connection with the anomalies detected in the lepton cosmic-ray flux by Pamela and Fermi. Concentrating on supersymmetric models, we consider the effect of these nonstandard cosmologies in selecting a preferred mass scale for the lightest supersymmetric particle as a dark matter candidate, and the consequent impact on the interpretation of new physics discovered or excluded at the LHC. Finally, we examine a rather predictive model, the G2-MSSM, investigating some of the standard assumptions usually implemented in the solution of the Boltzmann equation for the dark matter component, including coannihilations. We question the hypothesis that kinetic equilibrium holds along the whole phase of dark matter generation, and the validity of the factorization usually implemented to rewrite the system of a coupled Boltzmann equation for each coannihilating species as a single equation for the sum of all the number densities. As a byproduct we develop here a formalism to compute the kinetic decoupling temperature in case of coannihilating particles, which can also be applied to other particle physics frameworks, and also to standard thermal relics within a standard cosmology.

We develop a fast technique based on the generalized slow-roll (GSR) approach for computing the curvature bispectrum of inflationary models with features. We show that all triangle configurations can be expressed in terms of three simple integrals over the inflationary background with typical accuracy of better than $\sim 20\%$. With a first-order GSR approach the typical accuracy can be improved to better than the $\sim 5\%$ level. We illustrate this technique with the step potential model that has been invoked to explain the WMAP temperature power spectrum glitches at $\ell \sim 20–40$ and show that the maximum likelihood model falls short of observability by more than a factor of 100 in amplitude. We also explicitly demonstrate that the bispectrum consistency relation with the local slope of the power spectrum is satisfied for these models. In the GSR approach, the bispectrum arises from integrals of nearly the same function of the background slow-roll parameters as the power spectrum but with a stronger weight to the epoch before horizon crossing. Hence this technique enables reverse engineering of models with large bispectrum but small power spectrum features.

The rate and manner of vacuum decay are calculated in an explicit flux compactification, including all thick-wall and gravitational effects. For landscapes built of many units of a single flux, the fastest decay is usually to discharge just one unit. By contrast, for landscapes built of a single unit each of many different fluxes, the fastest decay is usually to discharge all the flux at once, which destabilizes the radion and begets a bubble of nothing. By constructing the bubble of nothing as the limit in which ever more flux is removed, we gain new insight into the bubble’s appearance. Finally, we describe a new instanton that mediates simultaneous flux tunneling and decompactification. Our model is the thin-brane approximation to six-dimensional Einstein-Maxwell theory.

A new class of core-collapse supernovae (SNe) has been discovered in recent years by optical/infrared surveys; these SNe suggest the presence of one or more extremely dense ($\sim {10}^{5-11}{\mathrm{cm}}^{-3}$) shells of circumstellar material (CSM) on ${10}^{2-4}\mathrm{AU}$ scales. We consider the collisions of the SN ejecta with these massive CSM shells as potential cosmic-ray (CR) accelerators. If $\sim 10\%$ of the SN energy goes into CRs, multi-TeV neutrinos and/or GeV-TeV gamma rays almost simultaneous with the optical/infrared light curves are detectable for SNe at $\lesssim 20–30\mathrm{Mpc}$. A new type of coordinated multimessenger search for such transients of duration $\sim 1–10$ months is required; these may give important clues to the physical origin of such SNe and to CR acceleration mechanisms.

In this paper, we obtain a relation between the high-energy absorption cross section and the strong gravitational lensing for a static and spherically symmetric black hole. It provides us a possible way to measure the high-energy absorption cross section for a black hole from strong gravitational lensing through astronomical observation. More importantly, it allows us to compute the total energy emission rate for high-energy particles emitted from the black hole acting as a gravitational lens. It could tell us the range of the frequency, among which the black hole emits the most of its energy and the gravitational waves are most likely to be observed. We also apply it to the Janis-Newman-Winicour solution. The results suggest that we can test the cosmic censorship hypothesis through the observation of gravitational lensing by the weakly naked singularities acting as gravitational lenses.

We introduce the top-BESS model, which is the effective description of the strong electroweak symmetry breaking with a single new $SU(2{)}_{L+R}$ triplet vector resonance. The model is a modification of the BESS model in the fermion sector. The triplet couples to the third generation of quarks only. This approach reflects a possible extraordinary role of the top quark in the mechanism of electroweak symmetry breaking. The low-energy limits on the model parameters found provide hope for finding sizable signals in the LHC Drell-Yan processes as well as in the s-channel production processes at the ILC. However, there are regions of the model parameter space where the interplay of the direct and indirect fermion couplings can hide the resonance peak in a scattering process even though the resonance exists and couples directly to top and bottom quarks.

The forward-backward asymmetry $A_{\mathrm{FB}}^{t\overline{t}}$ in top quark production at the Tevatron has been observed to be anomalously large by both CDF and D0. It has been suggested that a model with a $W^{\prime }$ coupling to $td$ and $ub$ might explain this anomaly, and other anomalies in $B$ mesons. Single-top-quark production in this model is large, and arguably in conflict with Tevatron measurements. However the model might still be viable if $A_{\mathrm{FB}}^{t\overline{t}}$ is somewhat smaller than its current measured central value. We show that even with smaller couplings, the model can be discovered (or strongly excluded) at the LHC using the 2010 data sets. We find that a suitable charge-asymmetry measurement is a powerful tool that can be used to constrain this and other sources of anomalous single-top production, and perhaps other new high-energy charge-asymmetric processes.

We study new top flavor violating resonances that are singly produced in association with a top at the LHC. Such top flavor violating states could be responsible for the Tevatron top forward-backward asymmetry. Since top flavor violating states can directly decay to a top (or antitop) and jet, and are produced in conjunction with another (oppositely charged) top, the direct signature of such states is a $tj$ (or $\overline{t}j$) resonance in $t\overline{t}j$ events. In general, these states can be very light and have $\mathcal{O}(1)$ couplings to the top sector so that they are copiously produced. We present a search strategy and estimate the discovery potential at the early LHC by implementing the strategy on simulated data. For example, with $1{\mathrm{fb}}^{-1}$ at 7 TeV, we estimate that a $W^{\prime }$ coupling to $d_R{\overline{t}}_R$ can be constrained at the $3\sigma$ level for $g_R=1$ and $m_{W^{\prime }}=200\mathrm{GeV}$, weakening to $g_R=1.75$ for $m_{W^{\prime }}=600\mathrm{GeV}$. With the search we advocate here, a bound at a similar level could be obtained for top flavor violating $Z^{\prime }$s, as well as triplet and sextet diquarks.

We show how the Santana Amaral-Gay Ducati-Betemps-Soyez (AGBS) model, originally developed for deep inelastic scattering applied to HERA data on the proton structure function, can also describe the RHIC data on single inclusive hadron yield for $d+Au$ and $p+p$ collisions through a new simultaneous fit. The single inclusive hadron production is modeled through the color glass condensate, which uses the quark (and gluon) condensate amplitudes in momentum space. The AGBS model is also a momentum space model based on the asymptotic solutions of the Balitsky-Kovchegov equation, although a different definition of the Fourier transform is used. This aspect is overcome, and a description entirely in transverse momentum of both processes arises for the first time. The small difference between the simultaneous fit and the one for HERA data alone suggests that the AGBS model describes very well both kinds of processes and thus emerges as a good tool to investigate the inclusive hadron production data. We use this model for predictions at LHC energies, which agrees very well with available experimental data.

Using analytic techniques developed for Hamiltonian dynamical systems, we show that a certain classical string configuration in ${\mathrm{AdS}}_5\times X_5$ with $X_5$ in a large class of Einstein spaces is nonintegrable. This answers the question of integrability of string on such backgrounds in the negative. We consider a string localized in the center of ${\mathrm{AdS}}_5$ that winds around two circles in the manifold $X_5$.

We derive the three-loop dilatation operator of the flavor $SU(2)$ subsector of $\mathcal{N}=4$ supersymmetric Yang-Mills theory in the planar limit by a direct Feynman diagram calculation in $\mathcal{N}=1$ superspace. The transcendentality three contributions which appear in intermediate steps cancel among each other, leaving a rational result which confirms the predictions from integrability. We derive finiteness conditions that allow us to avoid the explicit evaluation of entire classes of Feynman graphs and also yield constraints on the D-algebra manipulations. Based on these results, we discover universal cancellation mechanisms. As a check for the consistency of our result, we verify the cancellation of all higher-order poles.

We derive a coordinate-independent formulation of the post-1-Newtonian approximation to general relativity. This formulation is a generalization of the Newton-Cartan geometric formulation of Newtonian gravity. It involves several fields and a connection, but no spacetime metric at the fundamental level. We show that the usual coordinate-dependent equations of post-Newtonian gravity are recovered when one specializes to asymptotically flat spacetimes and to appropriate classes of coordinates.

A new method to visualize the curvature of spacetime was recently proposed. This method finds the eigenvectors of the electric and magnetic components of the Weyl tensor and, in analogy to the field lines of electromagnetism, uses the eigenvectors’ integral curves to illustrate the spacetime curvature. Here we use this approach, along with well-known topological properties of fields on closed surfaces, to show that an arbitrary, radiating, asymptotically flat spacetime must have points near null infinity where the gravitational radiation vanishes. At the zeros of the gravitational radiation, the field of integral curves develops singular features analogous to the critical points of a vector field. We can, therefore, apply the topological classification of singular points of unoriented lines as a method to describe the radiation field. We provide examples of the structure of these points using linearized gravity and discuss an application to the extreme-kick black-hole-binary merger.

The thermodynamic and dynamical properties of a variable dark energy model with density scaling as ${\rho }_x\propto (1+z{)}^m$, $z$ being the redshift, are discussed following the outline of Jetzer et al. [P. Jetzer, D. Puy, M. Signore, and C. Tortora, Gen. Relativ. Gravit. 43, 1083 (2011).]. These kinds of models are proven to lead to the creation/disruption of matter and radiation, which affect the cosmic evolution of both matter and radiation components in the Universe. In particular, we have concentrated on the temperature-redshift relation of radiation, which has been constrained using a very recent collection of cosmic microwave background (CMB) temperature measurements up to $z\sim 3$. For the first time, we have combined this observational probe with a set of independent measurements (Supernovae Ia distance moduli, CMB anisotropy, large-scale structure and observational data for the Hubble parameter), which are commonly adopted to constrain dark energy models. We find that, within the uncertainties, the model is indistinguishable from a cosmological constant which does not exchange any particles with other components. Anyway, while temperature measurements and Supernovae Ia tend to predict slightly decaying models, the contrary happens if CMB data are included. Future observations, in particular, measurements of CMB temperature at large redshift, will allow to give firmer bounds on the effective equation of state parameter $w_{\mathrm{eff}}$ of this kind of dark energy model.

Recently, X. Chen et al. proposed a new approach to the gauge invariant decomposition of the nucleon spin into the helicity and orbital angular momentum of quarks and gluons. The key ingredient in their construction is the separation of the gauge field into physical and “pure gauge” parts. We suggest a simple separation scheme and show that the resulting gluon helicity coincides with the first moment of the conventional polarized gluon distribution measurable in high energy experiments.

The spontaneous breaking of the $SU(3{)}^5$ quark/lepton flavor symmetry by means of three multiplets of scalar “Yukawa fields” admits vacua with one $\mathcal{O}(1)$ and two vanishing vacuum expectation values for each multiplet. If the number of generations is equal to three, and only in this case, the vanishing vacuum expectation values are lifted to exponentially suppressed entries by the inclusion of symmetry invariant logarithmic terms. A strong hierarchy for the Yukawa couplings and a quark mixing matrix that approaches a diagonal form are obtained in a natural way from $\mathcal{O}(1)$ parameters. This scenario provides a concrete realization of the minimal flavor violation hypothesis.