We present general conditions on Dirac and Majorana mass terms under which a type-I seesaw mechanism can lead to three exactly massless neutrinos at the tree level. We depict several examples where the conditions are satisfied and relate some of them to an underlying $U(1)$ symmetry. We show that higher order corrections may generate the small observed masses and this may be achieved even when the heavy Majorana neutrinos are at the electroweak scale or a little higher.

The reaction $pp\to K^{+}+(\Lambda p)$ has been measured at $T_p=1.953\mathrm{GeV}$ and $\Theta =0°$ with a high missing-mass resolution in order to study the $\Lambda p$ final state interaction. Narrow $S=-1$ resonances predicted by bag model calculations are not visible in the missing-mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV.

The ${\Lambda }_b(udb)$ baryon is observed in the decay ${\Lambda }_b\to J/\psi \Lambda$ using $6.1{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions collected with the D0 detector at $\sqrt{s}=1.96\mathrm{TeV}$. The production fraction multiplied by the branching fraction for this decay relative to that for the decay $B^0\to J/\psi K_s^0$ is measured to be $0.345\pm 0.034(\mathrm{stat})\pm 0.033(\mathrm{syst})\pm 0.003(\mathrm{PDG})$. Using the world average value of $f(b\to B^0)·\mathcal{B}(B^0\to J/\psi K_s^0)=(1.74\pm 0.08)\times {10}^{-5}$, we obtain $f(b\to {\Lambda }_b)·\mathcal{B}({\Lambda }_b\to J/\psi \Lambda )=(6.01\pm 0.60(\mathrm{stat})\pm 0.58(\mathrm{syst})\pm 0.28(\mathrm{PDG}))\times {10}^{-5}$. This measurement represents an improvement in precision by about a factor of 3 with respect to the current world average.

In many strongly coupled systems, the infrared dynamics is described by different degrees of freedom from the ultraviolet. It is then natural to ask how operators written in terms of the microscopic variables are mapped to operators composed of the macroscopic ones. Certain types of operators, like conserved currents, are simple to map, and in supersymmetric theories one can also follow the chiral ring. In this paper, we consider supersymmetric theories and extend the mapping to anomalous currents (and gaugino bilinears). Our technique is completely independent of subtleties associated with the renormalization group, thereby shedding new light on previous approaches to the problem. We demonstrate the UV/IR mapping in several examples with different types of dynamics, emphasizing the uniformity and simplicity of the approach. Natural applications of these ideas include the effects of soft breaking on the dynamics of various theories and new models of electroweak symmetry breaking.

Photon-neutrino interactions arise quite naturally in noncommutative field theories. Such couplings are absent in ordinary field theory and imply experimental lower bounds on the energy scale ${\Lambda }_{\mathrm{NC}}\sim |\theta {|}^{-2}$ of noncommutativity. Using nonperturbative methods and a Seiberg-Witten map based covariant approach to noncommutative gauge theory, we obtain $\theta$-exact expressions for the interactions, thereby eliminating previous restrictions to low-energy phenomena. We discuss implications for plasmon decay, neutrino charge radii, big bang nucleosynthesis, and ultrahigh energy cosmic rays. Our results behave reasonably throughout all interaction energy scales, thus facilitating further phenomenological applications.

We consider a real massless scalar field in $1+1$ dimensions satisfying time-dependent Robin boundary condition at a static mirror. This condition can simulate moving reflecting mirrors whose motions are determined by the time dependence of the Robin parameter. We show that particles can be created from vacuum, characterizing in this way a dynamical Casimir effect.

The Aharonov-Bohm effect including spin-noncommutative effects is considered. At linear order in $\theta$, the magnetic field is gauge invariant although spatially strongly anisotropic. Despite this anisotropy, the Schrödinger-Pauli equation is separable through successive unitary transformations and the exact solution is found. The scattering amplitude is calculated and compared with the usual case. In the noncommutative Aharonov-Bohm case the differential cross section is independent of $\theta$.

The Higgs boson of the standard model is described by a set of off-diagonal components of the multidimensional metric tensor, as well as the gauge fields. In the low-energy limit, the basic properties of the Higgs boson are reproduced, including the shape of the potential and interactions with the gauge fields of the electroweak part of the standard model.

A new scheme for computing dynamical evolutions and gravitational radiations for intermediate-mass-ratio inspirals (IMRIs) based on an effective one-body (EOB) dynamics plus Teukolsky perturbation theory is built in this paper. In the EOB framework, the dynamic essentially affects the resulted gravitational waveform for a binary compact star system. This dynamic includes two parts. One is the conservative part, which comes from effective one-body reduction. The other part is the gravitational backreaction, which contributes to the shrinking process of the inspiral of a binary compact star system. Previous works used an analytical waveform to construct this backreaction term. Since the analytical form is based on post-Newtonian expansion, the consistency of this term is always checked by numerical energy flux. Here, we directly use numerical energy flux by solving the Teukolsky equation via the frequency-domain method to construct this backreaction term. The conservative correction to the leading order terms in mass-ratio is included in the deformed-Kerr metric and the EOB Hamiltonian. We try to use this method to simulate not only quasicircular adiabatic inspiral, but also the nonadiabatic plunge phase. For several different spinning black holes, we demonstrate and compare the resulted dynamical evolutions and gravitational waveforms.

Attempts to formulate a quantum theory of gravitation are collectively known as quantum gravity. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special relativity theories predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called generalized uncertainty principle (GUP). We have proposed a GUP consistent with string theory, black hole physics, and doubly special relativity theories and have showed that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it suggests that the space that confines it must be quantized, and in fact that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this may signal the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale. Because this influences all the quantum Hamiltonians in an universal way, it predicts quantum gravity corrections to various quantum phenomena. Therefore, in the present work we compute these corrections to the Lamb shift, simple harmonic oscillator, Landau levels, and the tunneling current in a scanning tunneling microscope.

We present a new numerical relativity code designed for simulations of compact binaries involving matter. The code is an upgrade of the BAM code to include general relativistic hydrodynamics and implements state-of-the-art high-resolution-shock-capturing schemes on a hierarchy of mesh refined Cartesian grids with moving boxes. We test and validate the code in a series of standard experiments involving single neutron star spacetimes. We present test evolutions of quasiequilibrium equal-mass irrotational binary neutron star configurations in quasicircular orbits which describe the late inspiral to merger phases. Neutron star matter is modeled as a zero-temperature fluid; thermal effects can be included by means of a simple ideal gas prescription. We analyze the impact that the use of different values of damping parameter in the Gamma-driver shift condition has on the dynamics of the system. The use of different reconstruction schemes and their impact in the post-merger dynamics is investigated. We compute and characterize the gravitational radiation emitted by the system. Self-convergence of the waves is tested, and we consistently estimate error bars on the numerically generated waveforms in the inspiral phase.

We propose to test the electric neutrality of neutrons by a new technique using the spectroscopy of quantum states of ultracold neutrons in the gravity potential above a vertical mirror. The new technique is an application of Ramsey’s method of separated oscillating fields to neutron’s quantum states in the gravity potential of the Earth. In the presence of an electric field $E_z$ parallel or antiparallel to the direction of the acceleration of the Earth, $g$, the energy of the quantum states changes due to an additional electrostatic potential if a neutron carries a nonvanishing charge. In the long run our new method has the potential to improve the current limit of ${10}^{-21}{q}_e$ for the electric charge of the neutron by 2 orders of magnitude.

We calculate the two-body decay rates of quirkonium states formed from quirks that acquire mass solely through electroweak symmetry breaking. We consider $SU(N{)}_{ic}$ infracolor with two flavors of quirks transforming under the electroweak group (but not QCD) of the standard model. In one case, the quirks are in a chiral representation of the electroweak group, while in the other case, a vectorlike representation. The differences in the dominant decay channels between “chiral quirkonia” versus “vectorlike quirkonia” are striking. Several chiral quirkonia states can decay into the unique two-body resonance channels $WH$, $ZH$, $t\overline{t}$, $t\overline{b}/b\overline{t}$, and $\gamma H$, which never dominate for vectorlike quirkonia. Additionally, the channels $WW$, $WZ$, $ZZ$, and $W\gamma$, are shared among both chiral and vectorlike quirkonia. Resonances of dileptons or light quarks (dijets) can dominate for some vectorlike quirkonia states throughout their mass range, while these modes never dominate for chiral quirkonia unless the decays into pairs of gauge or Higgs bosons are kinematically forbidden.

We study in detail the model by Isidori and Kamenik that is claimed to explain the top quark forward-backward asymmetry at Tevatron, provide GeV-scale dark matter (DM), and possibly improve the agreement between data and theory in Tevatron $W+jj$ events. We compute the DM thermal relic density, the spin-independent DM-nucleon scattering cross section, and the cosmic microwave background constraints on both Dirac and Majorana neutralino DM in the parameter space that explains the top asymmetry. A stable light neutralino is not allowed unless the local DM density is 3–4 times smaller than expected, in which case Dirac DM with mass around 3 GeV may be possible, to be tested by the Planck mission. The model predicts a too broad excess in the dijet distribution and a strong modification of the missing $E_T$ distribution in $W+jj$ events.

We study the effect of inhomogeneities on light propagation. The Sachs equations are solved numerically in the Swiss-cheese models with inhomogeneities modeled by the Lemaître-Tolman solutions. Our results imply that, within the models we study, inhomogeneities may partially mimic the accelerated expansion of the Universe provided the light propagates through regions with lower than the average density. The effect of inhomogeneities is small and full randomization of the photons’ trajectories reduces it to an insignificant level.

We examine a class of cylindrically symmetric solutions in Hořava-Lifshitz gravity. For the relativistic value of the coupling constant, $\lambda =1$, we find the hedgehog-type static black string solution with the nonvanishing radial shift in the Arnowitt-Deser-Misner-type decomposition of the spacetime metric. With zero radial shift, this solution corresponds to the usual Banados-Teitelboim-Zanelli (BTZ) black string in general relativity. However, unlike the general relativity case, the BTZ-type black strings do naturally exist in Hořava-Lifshitz gravity, without the need for any specific source term. We also find a rotating BTZ-type black string solution which requires the nonvanishing radial shift for its very existence. We calculate the mass and the angular momentum of this solution, using the canonical Hamiltonian approach. Next, we discuss the Lemos-type black string, which is inherent in general relativity with a negative cosmological constant, and present the static metric for any value of $\lambda >1/3$. Finally, we show that while, for $\lambda =1$, the entropy of the Lemos-type black string is given by one quarter of the horizon area, the entropy of the static BTZ-type black string is one half of its horizon area.

We present an efficient numerical code based on spectral methods to integrate the field equations of general Robinson-Trautmann spacetimes. The most natural basis functions for the spectral expansion of the metric functions are spherical harmonics. Using the values of appropriate combinations of the metric functions at the collocation points, we have managed to reduce expression swell when the number of spherical harmonics increases. Our numerical code runs with relatively little computational resources and the code tests have shown excellent accuracy and convergence. The code has been applied to situations of physical interest in the context of Robsinson-Trautmann geometries such as: perturbation of the exterior gravitational field of a spheroid of matter; perturbation of an initially boosted black hole; and the nonfrontal collision of two Schwarzschild black holes. In dealing with these processes we have derived analytical lower and upper bounds on the velocity of the resulting black hole and the efficiency of the gravitational wave extraction, respectively. Numerical experiments were performed to determine the forms of the gravitational waves and the efficiency in each situation of interest.

It has been shown that extremal Kerr black holes can be used as particle accelerators and arbitrarily high energy may be obtained near the event horizon. We study particle collisions near the event horizon (outer horizon) and Cauchy horizon (inner horizon) of a non-extremal Kerr black hole. First, we provide a general proof showing that particles cannot collide with arbitrarily high energies at the outer horizon. Second, we show that ultraenergetic collisions can occur near the inner horizon of a Kerr black hole with any spin parameter $a$.

In this paper we investigate to which extent noncommutativity, an intrinsically quantum property, may influence the Friedmann-Robertson-Walker cosmological dynamics at late times/large scales. To our purpose it will be enough to explore the asymptotic properties of the cosmological model in the phase space. Our recipe to build noncommutativity into our model is based in the approach of Ref. [4] and can be summarized in the following steps: i) the Hamiltonian is derived from the Einstein-Hilbert action (plus a self-interacting scalar field action) for a Friedmann-Robertson-Walker space-time with flat spatial sections, ii) canonical quantization recipe is applied, i.e., the mini-superspace variables are promoted to operators, and the WDW equation is written in terms of these variables, iii) noncommutativity in the mini-superspace is achieved through the replacement of the standard product of functions by the Moyal star product in the WDW equation, and, finally, iv) semiclassical cosmological equations are obtained by means of the WKB approximation applied to the (equivalent) modified Hamilton-Jacobi equation. We demonstrate, indeed, that noncommutative effects of the kind considered here can be those responsible for the present speed up of the cosmic expansion.

We consider the $k=1$ Friedman-Robertson-Walker (FRW) model within loop quantum cosmology, paying special attention to the existence of an ambiguity in the quantization process. In spatially nonflat anisotropic models such as Bianchi II and IX, the standard method of defining the curvature through closed holonomies is not admissible. Instead, one has to implement the quantum constraints by approximating the connection via open holonomies. In the case of flat $k=0$ FRW and Bianchi I models, these two quantization methods coincide, but in the case of the closed $k=1$ FRW model they might yield different quantum theories. In this manuscript we explore these two quantizations and the different effective descriptions they provide of the bouncing cyclic universe. In particular, as we show in detail, the most dramatic difference is that in the theory defined by the new quantization method, there is not one, but two different bounces through which the cyclic universe alternates. We show that for a “large” universe, these two bounces are very similar and, therefore, practically indistinguishable, approaching the dynamics of the “curvature-based” quantum theory.