We analyze the viability of the Zee-Babu model as an explanation of observed neutrino masses and mixings and the possibility that the model is confirmed or discarded in experiments planned for the very close future. The allowed parameter space is studied analytically by using some approximations and partial data. Then, a complete scanning of all parameters and constraints is performed numerically by using Monte Carlo methods. The cleanest signal of the model will be the detection of the doubly charged scalar at the LHC and its correlation with measurements of the branching ratio of $\mu \to e\gamma$ at the MEG experiment. In addition, the model offers interesting predictions for ${\tau }^{-}\to {\mu }^{+}{\mu }^{-}{\mu }^{-}$ experiments, lepton-hadron universality tests, the ${\theta }_{13}$ mixing in neutrino oscillations and the $⟨m_{\nu }{⟩}_{ee}$ parameter of neutrinoless double beta decay.

We search for a third generation vector leptoquark ($VLQ3$) that decays to a $b$ quark and tau lepton using the CDF II detector and $320{\mathrm{pb}}^{-1}$ of integrated luminosity from the Fermilab Tevatron. Observing a number of events in agreement with standard model expectations, we obtain, assuming Yang-Mills (minimal) couplings, the most stringent upper limit on the $VLQ3$ pair production cross section of 344 fb (493 fb) and lower limit on the $VLQ3$ mass of $317\mathrm{GeV}/c^2$ ($251\mathrm{GeV}/c^2$) at 95% C.L.

We propose an extension of the standard model, in which neutrinos are Dirac particles and their tiny masses originate from a one-loop radiative diagram. The new fields required by the neutrino mass generation also accommodate the explanation for the matter-antimatter asymmetry and dark matter in the Universe.

We impose the periodicity conditions corresponding to the Matsubara formalism for thermal field theory as constraints in the imaginary-time path integral. These constraints are introduced by means of time-independent auxiliary fields which, by integration of the original variables, become dynamical fields in the resulting “dual” representation for the theory. This alternative representation has the appealing property of involving fields that live in one dimension less than the original ones, with a quantum partition function whose integration measure is identical to the one of its classical counterpart, albeit with a different (spatially nonlocal) action.

We conjecture an intrinsic UV cutoff for the validity of the effective field theory with a large number of species coupled to gravity. In four dimensions such an UV cutoff takes the form $\Lambda =\sqrt{\lambda /N}{M}_p$ for $N$ scalar fields with the same potential $\lambda {\varphi }_i^4$, $i=1,\dots ,N$. This conjecture implies that the assisted chaotic inflation or $N$-flation might be in the swampland, not in the landscape. Similarly an UV cutoff $\Lambda =g{M}_p/\sqrt{N}$ is conjectured for the U(1) gauge theory with $N$ species.

The main goal of this work is to investigate the possibility of finding the supersymmetric version of the U(1)-global string model which behaves as a vortex-superfluid. To describe the superfluid phase, we introduce a Lorentz-symmetry breaking background that, in an approach based on supersymmetry, leads to a discussion on the relation between the violation of Lorentz symmetry and explicit soft supersymmetry breakings. We also study the relation between the string configuration and the vortex-superfluid phase. In the framework we settle down in terms of superspace and superfields, we actually establish a duality between the vortex degrees of freedom and the component fields of the Kalb-Ramond superfield. We make also considerations about the fermionic excitations that may appear in connection with the vortex formation.

In anticipation of a subsequent application to QCD, we consider the case of QED at high temperature. We introduce a Fradkin representation into the exact, Schwingerian, functional expression of a fermion propagator, as well as a new and relevant version of the Bloch-Nordsieck model, which extracts the soft contributions of every perturbative graph, in contradistinction to the assumed separation of energy scales of previous semiperturbative treatments. Our results are applicable to the absorption of a fast particle which enters a heat bath, as well as to the propagation of a symmetric pulse within the thermal medium due to the appearance of an instantaneous, shockwave-like source acting in the medium. An exponentially decreasing time dependence of the incident particle’s initial momentum combines with a stronger decrease in the particle’s energy, estimated by a sum over all Matsubara frequencies, to model an initial “fireball,” which subsequently decays in a Gaussian fashion. When extended to QCD, qualitative applications could be made to RHIC scattering, in which a fireball appears, expands, and is damped away.

We study static, spherically symmetric black hole solutions of the Einstein equations with a positive cosmological constant and a conformally coupled self-interacting scalar field. Exact solutions for this model found by Martínez, Troncoso, and Zanelli were subsequently shown to be unstable under linear gravitational perturbations, with modes that diverge arbitrarily fast. We find that the moduli space of static, spherically symmetric solutions that have a regular horizon—and satisfy the weak and dominant energy conditions outside the horizon—is a singular subset of a two-dimensional space parametrized by the horizon radius and the value of the scalar field at the horizon. The singularity of this space of solutions provides an explanation for the instability of the Martínez, Troncoso, and Zanelli spacetimes and leads to the conclusion that, if we include stability as a criterion, there are no physically acceptable black hole solutions for this system that contain a cosmological horizon in the exterior of its event horizon.

Color octet (pseudo)scalars, if they exist, will be copiously produced at the CERN Large Hadron Collider (LHC). However, their detection can become a very challenging task. In particular, if their decay into a pair of top quarks is kinematically forbidden, the main decay channel would be into two jets, with a very large background. In this brief report we explore the possibility of using anomaly-induced decays of the color octet pseudoscalars into gauge bosons to find them at the LHC.

In this article we examine the layer phase of the five-dimensional, anisotropic, Abelian gauge model. Our results are to be compared with the ones of the 4D U(1) gauge model in an attempt to verify that four-dimensional physics governs the four-dimensional layers. The main results are as follows: (i) From the analysis of Wilson loops we verified the $\frac{1}{R}$ behavior, in the layered phase, for the potential between heavy charges. The renormalized fine structure constant in the layer phase is found to be equal to that of the 4D Coulomb phase, ${\alpha }_{\mathrm{layer}}={\alpha }_{4\mathrm{D}}$. (ii) Based on the helicity modulus analysis we show that the layers are in the Coulomb phase while the transverse bulk space is in the confining phase. We also calculated the renormalized coupling ${\beta }_R$ and found results compatible with those obtained from the Coulomb potential. Finally, we calculated the potential in the 5D Coulomb phase and found $\frac{1}{R^2}$ behavior for the static $q\overline{q}$ potential. From the study of the helicity modulus we have a possible estimate for the five-dimensional renormalized fine structure constant in the region of the critical value of the bare gauge coupling.

We extend the Polyakov-Nambu-Jona-Lasinio model for two degenerate flavors by including the effect of the SU(3) measure with a Vandermonde term. This ensures that the Polyakov loop always remains in the domain [0, 1]. The pressure, energy density, specific heat, speed of sound, and conformal measure show small or negligible effects from this term. However various quark number and isospin susceptibilities are all found to approach their respective ideal gas limits around $2T_c$. We compare our methods with other similar approaches in Polyakov-Nambu-Jona-Lasinio model and also present a quantitative comparison with lattice QCD data.

We present a detailed study of $B\to K_1(1270)\gamma$ and $B\to K_1(1400)\gamma$ decays. Using the light-cone sum rule technique, we calculate the $B\to K_{1A}(1^3{P}_1)$ and $B\to K_{1B}(1^1{P}_1)$ tensor form factors, $T_1^{K_{1A}}(0)$ and $T_1^{K_{1B}}(0)$, where the contributions are included up to the first order in $m_{K_1}/m_b$. We resolve the sign ambiguity of the $K_1(1270)–K_1(1400)$ mixing angle ${\theta }_{K_1}$ by defining the signs of decay constants, $f_{K_{1A}}$ and $f_{K_{1B}}^{\perp }$. From the comparison of the theoretical calculation and the data for decays $B\to K_1\gamma$ and ${\tau }^{-}\to K_1^{-}(1270){\nu }_{\tau }$, we find that ${\theta }_{K_1}=-(34\pm 13)°$ is favored. In contrast to $B\to K^{*}\gamma$, the hard-spectator contribution suppresses the $B\to K_1(1270)\gamma$ and $B\to K_1(1400)\gamma$ branching ratios slightly. The predicted branching ratios are in agreement with the Belle measurement within the errors. We point out that a more precise measurement for the ratio $R_{K_1}=\mathcal{B}(B\to K_1(1400)\gamma )/\mathcal{B}(B\to K_1(1270)\gamma )$ can offer a better determination for the ${\theta }_{K_1}$, and consequently the theoretical uncertainties can be reduced.

Using $281{\mathrm{pb}}^{-1}$ of data collected with the CLEO-c detector, we present new measurements of Cabibbo-suppressed decays of $D^0$ and $D^{+}$ mesons to $\eta$ and ${\eta }^{\prime }$ final states. We make first observations of $D^0\to {\eta }^{\prime }{\pi }^0$, $\eta \eta$, $\eta {\eta }^{\prime }$, and $\eta {\pi }^{+}{\pi }^{-}$, and find evidence for $D^{+}\to \eta {\pi }^{+}{\pi }^0$, $D^{+}\to {\eta }^{\prime }{\pi }^{+}{\pi }^0$, and $D^0\to {\eta }^{\prime }{\pi }^{+}{\pi }^{-}$. We also report on improved measurements of $D^0\to \eta {\pi }^0$, $D^{+}\to \eta {\pi }^{+}$, and $D^{+}\to {\eta }^{\prime }{\pi }^{+}$. Using the measured two-body Cabibbo-suppressed decays, we extract amplitudes for specific flavor topologies and compare them to those from Cabibbo-favored decays.

Analyzing the one-loop partition function, we discuss possible Kaluza-Klein (KK) states in the orbifold compactification of the heterotic string theory, toward the application to the threshold correction. The KK massive states associated with (relatively) large extra dimensions can arise only in nonprime orbifolds. The Gliozzi-Scherk-Olive (GSO) projection condition by a shift vector $V^I$ is somewhat relaxed above the compactification scale $1/R$. We also present the other condition on Wilson line $W$, $P·W=\mathrm{\text{integer}}$. With the knowledge of the partition function, we obtain the threshold corrections to gauge couplings, which include the Wilson line effects. We point out the differences in string and field theoretic orbifolds.

Attempts to construct chromodyons—objects with both magnetic charge and non-Abelian electric charge—in the context of spontaneously broken gauge theories have been thwarted in the past by topological obstructions to globally defining the unbroken non-Abelian “color” subgroup. In this paper we consider the possibility of chromodyons in a theory with SO(5) broken to $\mathrm{SU}(2)\times \mathrm{U}(1)$, where the topological obstructions are absent. We start by constructing a monopole with only magnetic charge. By exciting a global gauge zero mode about this monopole, we obtain a chromodyonic configuration that is an approximate solution of the field equations. We then numerically simulate the time evolution of this initial state, to see if it settles down in a stationary solution. Instead, we find that chromoelectric charge is continually radiated away, with every indication that this process will continue until this charge has been completely lost. We argue that this presents strong evidence against the existence of stable chromodyons.

Oscillons, extremely long-lived localized oscillations of a scalar field, are shown to be produced by evolving domain wall networks in ${\varphi }^4$ theory in two spatial dimensions. We study the oscillons in frequency space using the classical spectral function at zero momentum, and obtain that the velocity distribution is suppressed as ${\gamma }^{-2}$ at large Lorentz factor $\gamma$, with oscillons produced up to at least $\gamma \sim 10$. This leads us to speculate that oscillons are produced at cusps, regions of the domain wall travelling near the speed of light. In order to gain some insight onto the dilute oscillon “gas” produced by the domain walls, we prepare a denser gas by filling the simulation volume with oscillons boosted in random directions. We finish the study by revisiting collisions between oscillons and between an oscillon and a domain wall, showing that in the latter case they can pass straight through with minimal distortion.

To investigate the viability of the 4th root trick for the staggered fermion determinant in a simpler setting, we consider a 2-taste (flavor) lattice fermion formulation with no taste mixing but with exact taste-nonsinglet chiral symmetries analogous to the taste-nonsinglet $\mathrm{U}(1{)}_A$ symmetry of staggered fermions. Creutz’s objections to the rooting trick apply just as much in this setting. To counter them we show that the formulation has robust would-be zero modes in topologically nontrivial gauge backgrounds, and that these manifest themselves in a viable way in the rooted fermion determinant and also in the disconnected piece of the pseudoscalar meson propagator as required to solve the U(1) problem. Also, our rooted theory is heuristically seen to be in the right universality class for QCD if the same is true for an unrooted mixed fermion action theory.

A uniformly accelerating observer perceives the Minkowski vacuum state as a thermal bath of radiation. We point out that this field-theory effect can be derived, for any dimension higher than two, without actually invoking very high energy physics. This supports the view that this phenomenon is robust against Planck-scale physics and, therefore, should be compatible with any underlying microscopic theory.

In this paper we review the problem of time delay of photons propagating in a spacetime with a metric that explicitly depends on the energy of the particles (gravity-rainbow approach). We show that corrections due to this approach—which is closely related to the double special relativity proposal—produce for small redshifts ($z\ll 1$) smaller time delays than in the generic Lorentz invariance violating case.

Recently Vaganov and Hammersley investigated independently the equilibrium self-gravitating radiation in higher $(d\ge 4)$-dimensional, spherically symmetric anti–de Sitter space. It was found that in $4\le d\le 10$, there exist locally stable radiation configurations all the way up to a maximum red-shifted temperature, above which there are no solutions; there is also a maximum mass and maximum entropy configuration occurring at a higher central density than the maximal temperature configuration. Beyond their peaks the temperature, mass, and entropy undergo an infinite series of damped oscillations, which indicates the configurations in this range are unstable. In $d\ge 11$, the temperature, mass, and entropy of the self-gravitating configuration are monotonic functions of the central energy density, asymptoting to their maxima as the central density goes to infinity. In this paper we investigate the equilibrium self-gravitating radiation in higher-dimensional, plane-symmetric anti–de Sitter space. We find that there exist essential differences from the spherically symmetric case: In each dimension ($d\ge 4$), there are maximal mass (density), maximal entropy (density), and maximal temperature configurations; they do not appear at the same central energy density; the oscillation behavior appearing in the spherically symmetric case does not happen in this case; and the mass (density), as a function of the central energy density, increases first and reaches its maximum at a certain central energy density and then decreases monotonically in $4\le d\le 7$, while in $d\ge 8$, besides the maximum, the mass (density) of the equilibrium configuration has a minimum: the mass (density) first increases and reaches its maximum, then decreases to its minimum, and then increases to its asymptotic value monotonically. The reason causing the difference is discussed.