Nonequilibrium instabilities are known to lead to exponential amplification of boson occupation numbers for low-momentum modes on time scales much shorter than the asymptotic thermal equilibration time. We show for Yukawa-type interactions that this growth induces very efficient fermion production, which proceeds with the maximum primary boson growth rate. The description is based on a $1/N$ expansion of the 2PI effective action to next-to-leading order including boson-fermion loops, which are crucial to observe this phenomenon. For long enough amplification in the boson sector, fermion production terminates when the thermal occupancy is reached in the infrared. At higher momenta, where boson occupation numbers are low, the fermion modes exhibit a power-law regime with exponent two.

We investigate the chiral dynamics of gauge theories developing an infrared stable fixed point. We determine the dependence of the bilinear fermion condensate on the underlying fermion mass and its anomalous dimension. We introduce the instanton contributions and investigate how they affect the dynamics near the fixed point. We generalize the Gell-Mann Oakes Renner relation and suggest to use it to uncover the presence of an infrared fixed point of the underlying gauge theory. Our results have an immediate impact on the construction of sensible extensions of the standard model of particle interactions and the general understanding of the phase diagram of strongly coupled theories.

In this work we study the lepton flavor violating (LFV) semileptonic $\tau \to \mu f_0(980)$ decay within the context of SUSY-Seesaw Models, where the MSSM spectrum is extended by three right-handed neutrinos and their SUSY partners, and where the seesaw mechanism is used to generate the neutrino masses. We estimate its decay rate when it proceeds via the Higgs-mediated channel $\tau \to \mu H^{*}\to \mu f_0(980)$, where $H$ refers to the $CP$-even MSSM Higgs bosons $h^0$ and $H^0$, and the lepton flavor violating $\tau \mu H$ vertex is radiatively generated via SUSY loops. In order to describe the $f_0(980)$ meson we follow the guidelines from chiral constraints. As an implication of our computation, we explore the sensitivity to the Higgs sector in this decay and compare it with other LFV tau decay channels. The confrontation of our predictions for $\mathrm{BR}(\tau \to \mu f_0(980))$ with its very competitive present experimental bound leads us to extract some interesting restrictions on the most relevant model parameters, particularly, $\tan \beta$ and $m_{H^0}$.

If the canonical seesaw mechanism alone is responsible for neutrino mass, i.e. $m_{\nu }\simeq -m_D^2/m_N$, it would be difficult to prove at the TeV energy scale. A new verifiable mechanism of neutrino mass is proposed, using the inverse seesaw, with new physics at the TeV scale, such that $m_{\nu }\simeq m_D^2{ϵ}_L/m_N^2$, where ${ϵ}_L$ is a two-loop effect. Dark-matter candidates also appear naturally.

We compare the inclusive production of events containing a lepton ($\ell$), a photon ($\gamma$), significant transverse momentum imbalance (${\mathrm{E̸}}_T$), and a jet identified as containing a $b$-quark, to SM predictions. The search uses data produced in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $1.9{\mathrm{fb}}^{-1}$ of integrated luminosity taken with the CDF detector. We find 28 $\ell \gamma b{\mathrm{E̸}}_T$ events versus an expectation of ${31.0}_{-3.5}^{+4.1}$ events. If we further require events to contain at least three jets and large total transverse energy, the largest SM source is radiative top-quark pair production, $t\overline{t}+\gamma$. In the data we observe 16 $t\overline{t}\gamma$ candidate events versus an expectation from SM sources of ${11.2}_{-2.1}^{+2.3}$. Assuming the difference between the observed number and the predicted non-top-quark total of ${6.8}_{-2.0}^{+2.2}$ is due to SM top-quark production, we estimate the $t\overline{t}\gamma$ cross section to be $0.15\pm 0.08\mathrm{pb}$.

Nonrelativistic second-order corrections to the wave function at the origin in muonic and exotic atoms are considered. The corrections are due to the electronic vacuum polarization. Such corrections are of interest due to various effective approaches, which take into account QED and hadronic effects. The wave function at the origin plays a key role in the calculation of the pionium lifetime, various finite nuclear size effects, and the hyperfine splitting. The results are obtained for the $1s$ and $2s$ states in pionic and muonic hydrogen and deuterium and in pionium, a bound system of ${\pi }^{+}$ and ${\pi }^{-}$. Applications to the hyperfine structure and the Lamb shift in muonic hydrogen are also considered.

We exhibit a nonrelativistic ideal gas with a Kaluza–Klein tower of species, featuring a singular behavior of thermodynamic functions at zero chemical potential. In this way, we provide a qualitative match to the thermodynamics of recently found black holes in backgrounds with asymptotic nonrelativistic conformal symmetry.

We propose to use the second Hopf map for the reduction [via $SU(2)$ group action] of the eight-dimensional $\mathcal{N}=8$ supersymmetric mechanics to five-dimensional supersymmetric systems specified by the presence of an $SU(2)$ Yang monopole. For our purpose we develop the relevant reduction procedure. The reduced system is characterized by its invariance under the $\mathcal{N}=5$ or $\mathcal{N}=4$ supersymmetry generators (with or without an additional conserved Becchi-Rouet-Stora-Tyutin charge operator) which commute with the $su(2)$ generators.

We analyze the Hamiltonian time evolution of classical SU(2) Yang-Mills-Higgs theory with a fundamental Higgs doublet on a spacial lattice. In particular, we study energy transfer and equilibration processes among the gauge and Higgs sectors, calculate the maximal Lyapunov exponents under randomized initial conditions in the weak-coupling regime, where one expects them to be related to the high-temperature plasmon damping rate, and investigate their energy and coupling dependence. We further examine finite-time and finite-size errors, study the impact of the Higgs fields on the instability of constant non-Abelian magnetic fields, and comment on the implications of our results for the thermalization properties of hot gauge fields in the presence of matter.

We present two methods to include the asymptotic domain of a background spacetime in null directions for numerical solutions of evolution equations so that both the radiation extraction problem and the outer boundary problem are solved. The first method is based on the geometric conformal approach, the second is a coordinate based approach. We apply these methods to the case of a massless scalar wave equation on a Kerr spacetime. Our methods are designed to allow existing codes to reach the radiative zone by including future null infinity in the computational domain with relatively minor modifications. We demonstrate the flexibility of the methods by considering both Boyer-Lindquist and ingoing Kerr coordinates near the black hole. We also confirm numerically predictions concerning tail decay rates for scalar fields at null infinity in Kerr spacetime due to Hod for the first time.

We study exact solutions of nonlinear electrodynamics coupled to three-dimensional gravity with torsion. We show that in any static and spherically symmetric configuration, at least one component of the electromagnetic field has to vanish. In the electric sector of the theory, we construct an exact solution, characterized by the azimuthal electric field. When the electromagnetic action is modified by a topological mass term, we find two types of the self-dual solutions.

A black hole casts a shadow as an optical appearance because of its strong gravitational field. We study how to determine the spin parameter and the inclination angle by observing the apparent shape of the shadow, which is distorted mainly by those two parameters. Defining some observables characterizing the apparent shape (its radius and distortion parameter), we find that the spin parameter and inclination angle of a Kerr black hole can be determined by the observation. This technique is also extended to the case of a Kerr naked singularity.

We show that the quasi-Euclidean sections of various rotating black holes in different dimensions possess at least one nonconformal negative mode when thermodynamic instabilities are expected. The boundary conditions of the fixed induced metric correspond to the partition function of the grand-canonical ensemble. Indeed, in the asymptotically flat cases, we find that a negative mode persists even if the specific heat at constant angular momenta is positive, since the stability in this ensemble also requires the positivity of the isothermal moment of inertia. We focus, in particular, on Kerr black holes, on Myers-Perry black holes in five and six dimensions, and on the Emparan-Reall black ring solution. We go on further to consider the richer case of the asymptotically AdS Kerr black hole in four dimensions, where thermodynamic stability is expected for a large enough cosmological constant. The results are consistent with previous findings in the nonrotation limit and support the use of quasi-Euclidean instantons to construct gravitational partition functions.

A detailed analysis of gravitational slip, a new post-general relativity cosmological parameter characterizing the degree of departure of the laws of gravitation from general relativity on cosmological scales, is presented. This phenomenological approach assumes that cosmic acceleration is due to new gravitational effects; the amount of spacetime curvature produced per unit mass is changed in such a way that a universe containing only matter and radiation begins to accelerate as if under the influence of a cosmological constant. Changes in the law of gravitation are further manifest in the behavior of the inhomogeneous gravitational field, as reflected in the cosmic microwave background, weak lensing, and evolution of large-scale structure. The new parameter ${\varpi }_0$ is naively expected to be of order unity. However, a multiparameter analysis, allowing for variation of all of the standard cosmological parameters, finds that ${\varpi }_0={0.09}_{-0.59}^{+0.74}(2\sigma )$, where ${\varpi }_0=0$ corresponds to a cosmological constant plus cold dark matter universe under general relativity. Future probes of the cosmic microwave background (Planck) and large-scale structure (Euclid) may improve the limits by a factor of 4.

We investigate the breaking of global statistical isotropy caused by a dark energy component with an energy-momentum tensor which has point symmetry, that could represent a cubic or hexagonal crystalline lattice. In such models Gaussian, adiabatic initial conditions created during inflation can lead to anisotropies in the cosmic microwave background whose spherical harmonic coefficients are correlated, contrary to the standard assumption. We develop an adaptation of the line of sight integration method that can be applied to models where the background energy-momentum tensor is isotropic, but whose linearized perturbations are anisotropic. We then show how this can be applied to the cases of cubic and hexagonal symmetry. We compute quantities which show that such models are indistinguishable from isotropic models even in the most extreme parameter choices, in stark contrast to models with anisotropic initial conditions based on inflation. The reason for this is that the dark energy based models contribute to the CMB anisotropy via the integrated Sachs-Wolfe effect, which is only relevant when the dark energy is dominant, that is, on the very largest scales. For inflationary models, however, the anisotropy is present on all scales.

We show that higher-order actions for cosmological perturbations in the multifield Dirac-Born-Infeld (DBI) inflation model are obtained by a Lorentz boost from the rest frame of the brane to the frame where the brane is moving. We confirm that this simple method provides the same third- and fourth-order actions at leading order in slow roll and in the small sound speed limit as those obtained by the usual Arnowitt-Deser-Misner formalism. As an application, we compute the leading order connected four-point function of the primordial curvature perturbation coming from the intrinsic fourth-order contact interaction in the multifield DBI-inflation model. At third order, the interaction Hamiltonian arises purely by the boost from the second-order action in the rest frame of the brane. The boost acts on the adiabatic and entropy modes in the same way, thus there exists a symmetry between the adiabatic and entropy modes. But at fourth order this symmetry is broken due to the intrinsic fourth-order action in the rest frame and the difference between the Lagrangian and the interaction Hamiltonian. Therefore, contrary to the three-point function, the momentum dependence of the purely adiabatic component and the components including the entropic contributions are different in the four-point function. This suggests that the trispectrum can distinguish the multifield DBI-inflation model from the single field DBI-inflation model.

We consider the effect of accretion of radiation in the early Universe on primordial black holes in Brans-Dicke theory. The rate of growth of a primordial black hole due to accretion of radiation in Brans-Dicke theory is considerably smaller than the rate of growth of the cosmological horizon, thus making available sufficient radiation density for the black hole to accrete causally. We show that accretion of radiation by Brans-Dicke black holes overrides the effect of Hawking evaporation during the radiation dominated era. The subsequent evaporation of the black holes in later eras is further modified due to the variable gravitational “constant,” and they could survive up to longer times compared to the case of standard cosmology. We estimate the impact of accretion on modification of the constraint on their initial mass fraction obtained from the $\gamma$-ray background limit from presently evaporating primordial black holes.

The amplification of the primordial magnetic fields and the gravitational baryogenesis, a mechanism that allows one to generate the baryon asymmetry in the Universe by means of the coupling between the Ricci scalar curvature and the baryon current, are reviewed in the framework of the nonlinear electrodynamics. To study the amplification of the primordial magnetic field strength, we write down the gauge invariant wave equations and then solve them (in the long wavelength approximation) for three different eras of the Universe: de Sitter, the reheating, and the radiation-dominated era. Constraints on parameters entering the nonlinear electrodynamics are obtained by using the amplitude of the observed galactic magnetic fields and the baryon asymmetry, which are characterized by the dimensionless parameters $r\sim {10}^{-37}$ and ${\eta }_B\lesssim 9\times {10}^{-11}$, respectively.

We explore the problems of propagation, confinement, and anisotropy of ultrahigh-energy cosmic rays. Previous investigations of plasma-particle interactions are based on a first-order perturbation theory also known as quasilinear theory. It is the subject of this article to employ a nonlinear diffusion theory, namely, the second-order quasilinear theory. We compute the parallel mean free path for slab and for isotropic turbulence for a wave spectrum with small-wave-number cutoff. It is demonstrated that we obtain a finite parallel mean free path even if the Larmor radius of the charged particle is larger than the largest scale of turbulence. Therefore, charged cosmic rays of all energies can be scattered and confined to the Galaxy by the turbulent magnetic fields.

We show in the framework of the Higgs triplet model that the lower bound of the neutrino mass is obtained if we can measure $\frac{\Gamma ({\Delta }^{--}\to ee)}{\Gamma ({\Delta }^{--}\to \mu \mu )}$ at the LHC.