We propose a mechanism for relaxing a constraint on the number of messengers in low-scale gauge mediation models. The Landau pole problem for the standard-model gauge coupling constants in the low-scale gauge mediation can be circumvented by using our mechanism. An essential ingredient is a large positive anomalous dimension of messenger fields given by a large Yukawa coupling in a conformal field theory at high energies. The positive anomalous dimension reduces the contribution of the messengers to the beta function of the standard-model gauge couplings.

We consider a $3+1$ dimensional field theory at a Lifshitz point for a dynamical critical exponent $z=3$, with a scalar and a fermion field coupled via a Yukawa interaction. Using the nonperturbative Schwinger-Dyson approach we calculate quantum corrections to the effective action. We demonstrate that a first order derivative kinetic term as well as a mass term for the fermion arise dynamically. This signals the restoration of Lorentz symmetry in the IR regime of the single fermion model, although for theories with more than one fermionic species such a conclusion will require fine-tuning of couplings. The limitations of the model and our approach are discussed.

The problem of neutrino spin rotation in dense matter and in strong electromagnetic fields is solved in accordance with the basic principles of quantum mechanics. We obtain a complete system of wave functions for a massive Dirac neutrino with an anomalous magnetic moment which are the eigenfunctions of the kinetic momentum operator and have the form of nonspreading wave packets. These wave functions enable one to consider the states of neutrino with rotating spin as pure quantum states and can be used for calculating probabilities of various processes with the neutrino in the framework of the Furry picture.

In this work we consider the evolution of a massive scalar field in cylindrically symmetric space-times. Quasinormal modes have been calculated for static and rotating cosmic cylinders. We found unstable modes in some cases. Rotating as well as static cosmic strings, i.e., without regular interior solutions, do not display quasinormal oscillation modes. We conclude that rotating cosmic cylinder space-times that present closed timelike curves are unstable against scalar perturbations.

We discuss the validity, or lack thereof, of the Jebsen-Birkhoff theorem in scalar-tensor theories by generalizing it and regarding the Brans-Dicke-like scalar as effective matter. Both the Jordan and Einstein frames are discussed and an apparent contradiction between static spherical solutions of scalar-tensor gravity and Hawking’s theorem on Brans-Dicke black holes is clarified. The results are applied to metric and Palatini $f(R)$ gravity.

We obtain a class of slowly rotating charged Kaluza-Klein black hole solutions of the five-dimensional Einstein-Maxwell-dilaton theory with arbitrary dilaton coupling constant. At infinity, the spacetime is effectively four dimensional. In the absence of the squashing function, our solution reduces to the five-dimensional asymptotically flat slowly rotating charged dilaton black hole solution with two equal angular momenta. We calculate the mass, the angular momentum, and the gyromagnetic ratio of these rotating Kaluza-Klein dilaton black holes. It is shown that the dilaton field and the nontrivial asymptotic structure of the solutions modify the gyromagnetic ratio of the black holes. We also find that the gyromagnetic ratio crucially depends on the dilaton coupling constant, $\alpha$, and decreases with increasing $\alpha$ for any size of the compact extra dimension.

We propose a general class of interacting models in which the interaction between the cold dark matter component and $\Lambda$ is parametrized by an arbitrary function of the cosmic scale factor $ϵ(a)$. Differently from other dynamical $\Lambda$ scenarios in which the final stage of cosmic expansion is a de Sitter phase, we find solutions of transient acceleration, in which the $\Lambda$-dark matter interaction will drive the Universe to a new dark matter-dominated era in the future. We investigate some cosmological consequences of this model and discuss some constraints on its parameters from current Type Ia aupernovae, baryonic acoustic oscillations, CMB, and $H_0$ data.

In addition to gamma rays, dark matter annihilation products can include energetic electrons which inverse Compton scatter with the cosmic microwave background to produce a diffuse extragalactic background of gamma rays and x rays. In models in which the dark matter particles annihilate primarily to electrons or muons, the measurements of EGRET and COMPTEL can provide significant constraints on the annihilation cross section. The Fermi gamma-ray space telescope will likely provide an even more stringent test of such scenarios.

The principles of a previously developed formalism for the covariant treatment of multiscalar fields for which (as in a nonlinear sigma model) the relevant target space is not of affine type—but curved—are recapitulated. Their application is extended from ordinary harmonic models to a more general category of harmonious field models, with emphasis on cases in which the field is confined to a string or higher brane world sheet, and for which the relevant internal symmetry group is non-Abelian, so that the conditions for conservation of the corresponding charge currents become rather delicate, particularly when the symmetry is gauged. Attention is also given to the conditions for conservation of currents of a different kind—representing surface fluxes of generalized momentum or energy—associated with symmetries not of the internal target space but of the underlying space-time background structure, including the metric and any relevant gauge field. For the corresponding current to be conserved the latter need not be manifestly invariant: preservation modulo a gauge adjustment will suffice. The simplest case is that of “strong” symmetry, meaning invariance under the action of an effective Lie derivative (an appropriately gauge adjusted modification of an ordinary Lie derivative). When the effective symmetry is of the more general “weak” kind, the kinetic part of the current is not conserved by itself but only after being supplemented by a suitable contribution from the background.

A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We extend the solenoid analysis to cosmic strings and find enhanced radiation from cusps and kinks on loops. We argue by analogy with the electromagnetic AB interaction that cosmic strings should emit photons due to the gravitational AB interaction of fields in the conical spacetime of a cosmic string. We calculate the emission from a kink and find that it is of similar order as emission from a cusp, but kinks are vastly more numerous than cusps and may provide a more interesting observational signature.

The distinctive features of single field inflationary models with nonminimal kinetic terms, like Dirac-Born-Infeld and $k$ inflation, can be captured by more familiar multiple-field inflationary systems of the type that typically arise in low-energy supergravity models. At least one heavy field, which we call the gelaton, has an effective potential which depends on the kinetic energy of the inflaton. Integrating out the gelaton gives rise to an effectively single field system for which the speed of sound for the adiabatic fluctuations is reduced, generating potentially observable equilateral non-Gaussianity, while causing negligible isocurvature fluctuations. This mechanism is only active if there is a relatively tight coupling between the gelaton and the inflaton. Requiring that the inflaton-gelaton system remains weakly coupled puts an upper limit on the gelaton mass. This approach gives a potentially UV-completable framework for describing large classes of $k$-inflationary behavior.

Magnetic fields interact with gravitational waves in various ways. We consider the coupling between the Weyl and the Maxwell fields in cosmology and study the effects of the former on the latter. The approach is fully analytical and the results are gauge invariant. We show that the nature and the outcome of the gravitomagnetic interaction depends on the electric properties of the cosmic medium. When the conductivity is high, gravitational waves reduce the standard (adiabatic) decay rate of the $B$ field, leading to its superadiabatic amplification. In poorly conductive environments, on the other hand, Weyl-curvature distortions can result into the resonant amplification of large-scale cosmological magnetic fields. Driven by the gravitational waves, these $B$ fields oscillate with an amplitude that is found to diverge when the wavelengths of the two sources coincide. We present technical and physical aspects of the gravitomagnetic interaction and discuss its potential implications.

We consider the phonon contribution to the bulk viscosities ${\zeta }_1$, ${\zeta }_2$ and ${\zeta }_3$ of a cold relativistic superfluid. We assume the low temperature $T$ regime and that the transport properties of the system are dominated by the phonons. We use kinetic theory in the relaxation time approximation and the low energy effective field theory of the corresponding system. The parametric dependence of the bulk viscosity coefficients is fixed once the equation of state is specified, and the phonon dispersion law to cubic order in momentum is known. We first present a general discussion, valid for any superfluid, then we focus on the color-flavor locked superfluid because all the parameters needed in the analysis can be computed in the high density limit of QCD, and also because of the possible astrophysical applications. For the three independent bulk viscosity coefficients we find that they scale with the temperature as ${\zeta }_i\sim 1/T$, and that in the conformal limit only the third coefficient ${\zeta }_3$ is nonzero.

We consider the diffeomorphism invariant gravity coupled with the ideal fluid in the nonstandard way. The Lorentz invariance of the graviton propagator in such a theory considered as perturbation over flat background turns out to be broken due to the nonstandard coupling with the ideal fluid. As a result the behavior of the propagator in the ultraviolet/infrared region indicates that some versions of such theory are (super-)renormalizable ones (with appearance of only physical transverse modes). The Friedmann-Robertson-Walker cosmology in some cases may be different from the one in general relativity with the possible power law inflationary stage.

The lightest Higgs scalar boson mass in supersymmetry can be raised significantly by extra vectorlike quark and lepton supermultiplets with large Yukawa couplings but dominantly electroweak-singlet masses. I consider models of this type that maintain perturbative gauge coupling unification. The impact of the new particles on precision electroweak observables is found to be moderate, with the fit to $Z$-pole data as good or better than that of the standard model even if the new Yukawa couplings are as large as their fixed-point values and the extra vectorlike quark masses are as light as 400 GeV. I study the size of corrections to the lightest Higgs boson mass, taking into account the fixed-point behavior of the scalar trilinear couplings. I also discuss the decay branching ratios of the lightest new quarks and leptons and general features of the resulting collider signatures.

Supersymmetric $B-L$ extension of the standard model (SM) is one of the best candidates for physics beyond the SM that accounts for the TeV scale seesaw mechanism and provides an attractive solution for the Higgs naturalness problem. We analyze the charged lepton flavor violation (LFV) in this class of models. We show that, due to the smallness of Dirac neutrino Yukawa coupling, the decay rates of $l_i\to l_j\gamma$ and $l_i\to 3l_j$, generated by the renormalization group evolution of soft supersymmetry breaking terms from GUT to seesaw scale, are quite suppressed. Therefore, this model is free from the stringent LFV constraints usually imposed on the supersymmetric seesaw model. We also demonstrate that the right sneutrino is a long-lived particle and can be pair produced at the LHC through the $B-L$ gauge boson. Then, they decay into a same-sign dilepton, with a total cross section of order $\mathcal{O}(1)\mathrm{pb}$. This signal is one of the striking signatures of supersymmetric $B-L$ extension of the SM.

We study the effects of fermiophobic scalar/pseudoscalar oblique corrections on bound state energy levels in muonic atoms. To make the treatment sufficiently general, while including ordinary scalar and axionlike pseudoscalar fields as special cases, we consider unparticle scalar/pseudoscalar operators with couplings predominantly to photons. We derive the relevant vacuum polarization functions and comment on the functional forms of the unparticle Uehling potentials for various scaling dimensions in the point nucleus and finite nucleus approximations. It is estimated that for an infrared fixed point near the scale of electroweak-symmetry breaking, in the low TeV range, and natural values for the model parameters, the energy shifts in the low-lying muonic-lead transitions are typically of the order of a few times 0.1 eV to a few times 0.01 eV. The energy level structures of the unparticle Uehling shifts are inferred using general methods for the scalar and pseudoscalar cases and it is shown that the two cases contribute to the energy shifts with the same sign. It is shown that this conclusion is not changed even when scale invariance is broken and is in fact relatively insensitive to the scale at which it is broken. It is pointed out nevertheless that the estimated magnitude of the unparticle Uehling shift (based on some natural values for the model parameters) is a factor of 1000–10000 below the discrepancy in QED/nuclear theory and precision muonic-lead spectroscopy from about two decades ago. We briefly comment on scenarios where the unparticle induced energy shift, if it exists, may be experimentally measurable. One possibility in this direction is if the UV sector, from which the unparticle sector arises, has a large number of fermions. Comments are also made on the possibility of further studying muonic atoms, as a probe for beyond-standard-model physics, in the context of forthcoming experiments, such as those probing lepton flavor violation through coherent muon-electron conversions. For completeness we explore some of the astrophysical and cosmological consequences of a fermiophobic scalar/pseudoscalar unparticle sector. In the fermiophobic context we also estimate a minimum value for the conformal invariance breaking scale.

Using the nonperturbative renormalization technique, we calculate the renormalization factors for quark bilinear operators made of overlap fermions on the lattice. The background gauge field is generated by the JLQCD and TWQCD Collaborations, including dynamical effects of two or $2+1$ flavors of light quarks on a ${16}^3\times 32$ or ${16}^3\times 48$ lattice at lattice spacing around 0.1 fm. By reducing the quark mass close to the chiral limit, where the finite volume system enters the so-called $ϵ$ regime, the unwanted effect of spontaneous chiral symmetry breaking on the renormalization factors is suppressed. On the lattices in the conventional $p$ regime, this effect is precisely subtracted by separately calculating the contributions from the chiral condensate.

Using perturbation theory in the Euclidean (imaginary time) formalism as well as the nonperturbative Fujikawa method, we verify that the chiral anomaly equation remains unaffected in the presence of nonzero chemical potential, $\mu$. We extend our considerations to fermions with exact chiral symmetry on the lattice and discuss the consequences for the recent Bloch-Wettig proposal for the Dirac operator at finite chemical potential. We propose a new simpler method of incorporating $\mu$ and compare it with the Bloch-Wettig idea.