We study the same-sign top pair production mediated by the first Kaluza-Klein (KK) excitation of the gluon in the Randall-Sundrum model with flavor violation at the LHC, in which the nonuniversal couplings between fermions and KK gauge bosons will lead to observable tree-level flavor changing neutral current effects. We find that the same-sign top quarks produced in our case have property of high energy and high transverse momentum, and lead to an observable signal in the same-sign dilepton channel even when the mass of the KK gluon reach up to 3 TeV. We further investigate the potential of the LHC to probe the flavor violating parameters and find that the LHC can probe their values down to 0.06.

If a new massive vector boson with nonzero axial couplings to fermions will be observed at LHC, then an upper limit on the scale of new physics could be derived from unitarity of $\mathcal{S}$ matrix. The new physics will involve either new massive fermions, or scalars, or even a strongly coupled sector. We derive a model independent bound on the scale of new physics. If $M_G/g_A<3\mathrm{TeV}$ and the fermion is a top quark, the upper limit is 78 TeV.

In many theories of physics beyond the standard model, from extra dimensions to Hidden Valleys and models of dark matter, $Z^{\prime }$ bosons mediate between standard model particles and hidden sector states. We study the feasibility of observing such hidden states through an invisibly decaying $Z^{\prime }$ at the LHC. We focus on the process $pp\to \gamma Z^{\prime }\to \gamma X{X}^{†}$, where $X$ is any neutral, (quasi-) stable particle, whether a standard model neutrino or a new state. This complements a previous study using $pp\to Z{Z}^{\prime }\to {\ell }^{+}{\ell }^{-}X{X}^{†}$. Only the $Z^{\prime }$ mass and two effective charges are needed to describe this process. If the $Z^{\prime }$ decays invisibly only to standard model neutrinos, then these charges are predicted by observation of the $Z^{\prime }$ through the Drell-Yan process, allowing discrimination between $Z^{\prime }$ decays to standard model $\nu$’s and invisible decays to new states. We carefully discuss all backgrounds and systematic errors that affect this search. We find that hidden sector decays of a 1 TeV $Z^{\prime }$ can be observed at $5\sigma$ significance with $50{\mathrm{fb}}^{-1}$ at the LHC. Observation of a 1.5 TeV state requires super-LHC statistics of $1{\mathrm{ab}}^{-1}$. Control of the systematic errors, in particular, the parton distribution function uncertainty of the dominant $Z\gamma$ background, is crucial to maximize the LHC search reach.

We present a calculation of magnetic moments for selected spin-1 mesons using the techniques of lattice QCD. This is carried out by introducing a progressively small static magnetic field on the lattice and measuring the linear response of a hadron’s mass shift. The calculations are done on ${24}^4$ quenched lattices using standard Wilson actions, with $\beta =6.0$ and pion mass down to 500 MeV. The results are compared to those from the form factor method.

We calculate correlation functions of the energy-momentum tensor in the vicinity of the deconfinement phase transition of ($3+1$)-dimensional SU(2) gauge theory and discuss their critical behavior in the vicinity of the second order deconfinement transition. We show that correlation functions of the trace of the energy-momentum tensor diverge uniformly at the critical point in proportion to the specific heat singularity. Correlation functions of the pressure, on the other hand, stay finite at the critical point. We discuss the consequences of these findings for the analysis of transport coefficients, in particular, the bulk viscosity, in the vicinity of a second order phase transition point.

We calculate the semileptonic baryon octet-octet transition form factors using a manifestly Lorentz covariant quark model approach based on the factorization of the contribution of valence quarks and chiral effects. We perform a detailed analysis of SU(3)-breaking corrections to the hyperon semileptonic decay form factors. We present complete results on decay rates and asymmetry parameters including lepton mass effects for the rates.

We compare the inclusive transverse momentum spectra of single pions above $p_T=3\mathrm{GeV}/c$ measured in proton-proton ($p\mathrm{\text{−}}p$) collisions at $\sqrt{s}=21.7–23.8\mathrm{GeV}$, with next-to-leading-order (NLO) perturbative QCD (pQCD) predictions using recent parametrizations of the parton densities and parton-to-pion fragmentation functions. Although the dependence on the theoretical scales is large, the calculations can reproduce the experimental results both in magnitude and shape. Based on the existing data and on a pQCD $\sqrt{s}$ rescaling of the measured spectra, we provide a practical parametrization of the baseline $p\mathrm{\text{−}}p$ pion transverse momentum spectrum to be compared to nucleus-nucleus collisions data at $\sqrt{s_{NN}}=22.4\mathrm{GeV}$.

We study the supersymmetric version of the type-II seesaw mechanism assuming minimal supergravity boundary conditions. We calculate branching ratios for lepton flavor violating (LFV) scalar tau decays, potentially observable at the LHC, as well as LFV decays at low energy, such as $l_i\to l_j+\gamma$, and compare their sensitivity to the unknown seesaw parameters. In the minimal case of only one triplet coupling to the standard model lepton doublets, ratios of LFV branching ratios can be related unambiguously to neutrino oscillation parameters. We also discuss how measurements of soft SUSY breaking parameters at the LHC can be used to indirectly extract information of the seesaw scale.

We show that the measurements of 10 GeV atmospheric neutrinos by an upcoming array of densely-packed phototubes buried deep inside the IceCube detector at the South Pole can be used to determine the neutrino mass hierarchy for values of ${sin}^{2}2{\theta }_{13}$ close to the present bound, if the hierarchy is normal. These results are obtained for an exposure of 100 Mton years and systematic uncertainties up to 10%.

We present the observation of the decay $B^0\to {\chi }_{c0}{K}^{*0}$ as well as evidence of $B^{+}\to {\chi }_{c0}{K}^{*+}$, with an 8.9 and a 3.6 standard deviation significance, respectively, using a data sample of $454\times {10}^6$ ${\rm Y}(4\mathrm{S})\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II $B$ meson factory located at the Stanford Linear Accelerator Center (SLAC). The measured branching fractions are $\mathcal{B}(B^0\to {\chi }_{c0}{K}^{*0})=(1.7\pm 0.3\pm 0.2)\times {10}^{-4}$ and $\mathcal{B}(B^{+}\to {\chi }_{c0}{K}^{*+})=(1.4\pm 0.5\pm 0.2)\times {10}^{-4}$, where the first quoted errors are statistical and the second are systematic. We obtain a branching fraction upper limit of $\mathcal{B}(B^{+}\to {\chi }_{c0}{K}^{*+})<2.1\times {10}^{-4}$ at the 90% confidence level.

We study the generic intersection (or web) of vortices with instantons inside, which is a $1/4$ Bogomol’nyi-Prasad-Sommerfield state in the Higgs phase of five-dimensional $\mathcal{N}=1$ supersymmetric $U(N_{\mathrm{C}})$ gauge theory on ${\mathbb{R}}_t\times ({\mathbb{C}}^{*}{)}^2\simeq {\mathbb{R}}^{2,1}\times T^2$ with $N_{\mathrm{F}}=N_{\mathrm{C}}$ Higgs scalars in the fundamental representation. In the case of the Abelian-Higgs model ($N_{\mathrm{F}}=N_{\mathrm{C}}=1$), the intersecting vortex sheets can be beautifully understood in a mathematical framework of amoeba and tropical geometry, and we propose a dictionary relating solitons and gauge theory to amoeba and tropical geometry. A projective shape of vortex sheets is described by the amoeba. Vortex charge density is uniformly distributed among vortex sheets, and negative contribution to instanton charge density is understood as the complex Monge-Ampère measure with respect to a plurisubharmonic function on $({\mathbb{C}}^{*}{)}^2$. The Wilson loops in $T^2$ are related with derivatives of the Ronkin function. The general form of the Kähler potential and the asymptotic metric of the moduli space of a vortex loop are obtained as a by-product. Our discussion works generally in non-Abelian gauge theories, which suggests a non-Abelian generalization of the amoeba and tropical geometry.

In the present work we study dynamical space-time symmetries in noncommutative relativistic theories by using the minimal canonical extension of the Doplicher, Fredenhagen, and Roberts algebra. Our formalism is constructed in an extended space-time with independent degrees of freedom associated with the object of noncommutativity ${\theta }^{\mu \nu }$. In this framework we consider theories that are invariant under the Poincaré group $\mathcal{P}$ or under its extension ${\mathcal{P}}^{\prime }$, when translations in the extra dimensions are permitted. The Noether’s formalism adapted to such extended $x+\theta$ space-time is employed.

We investigate decoupling of heavy Kaluza-Klein (KK) modes in an Abelian Higgs model with space-time topologies ${\mathbb{R}}^{3,1}\times S^1$ and ${\mathbb{R}}^{3,1}\times S^1/{\mathbb{Z}}_2$. After integrating out only the heavy KK modes we find the one-loop, light-particle (irreducible) effective action (LPEA) for the zero-mode fields. We find that in the ${\mathbb{R}}^{3,1}\times S^1$ topology the heavy modes do not decouple in this low-energy effective action, due to the zero mode of the 5th component of the 5D gauge field $A_5$. Because $A_5$ is a scalar under 4D Lorentz transformations, there is no gauge symmetry protecting it from getting mass and $A_5^4$ interaction terms after loop corrections. In addition, after symmetry breaking, we find that the effective action has new divergences in the $A_5$ mass that did not appear in the symmetric phase. The new divergences are traced back to the gauge-goldstone mixing that occurs after symmetry breaking. We find that when considering low-energy physical processes, however, the divergences of the zero-mode loop diagrams will cancel the divergences in the effective action, rendering the radiatively corrected couplings finite. Although, this clears up the extra divergences in the $A_5$ sector, the gauge coupling still has a different compactification scale dependence in the $A_5$ then it does in the $A_{\mu }$ sector, leading to an explicit violation of decoupling. If instead of the LPEA one considers the Wilsonian effective action by integrating out zero modes of momenta $|p|>M$ ($M$ is the mass of the lowest KK excitation) in addition to the heavy modes, then decoupling is manifest. However, as is well known the price is the difficulty in maintaining 4D Lorentz and gauge invariance. In order to get a more sensible effective theory in the LPEA formalism, we investigate the $S^1/{\mathbb{Z}}_2$ compactification. With this kind of compact topology, the $A_5$ zero mode disappears. With no $A_5$, there are no new divergences and the heavy modes decouple. We also discuss the dependence of the couplings and masses on the compactification scale, and derive a set of renormalization group-like equations for the running of the effective couplings with respect to the compactification scale. It is found that magnitudes of both couplings decrease as the scale $M$ increases.

It is well known that there should be a total cancellation of the IR divergences in unitary interacting field theory, such as QED and gravity. The cancellation should be at all orders between loop and tree-level contributions to cross sections. This is the crucial fact related to the unitarity of the evolution operator (S-matrix) of the underlying interacting field theory. In this paper we show that such a cancellation does not happen in de Sitter space.

We study the lensing properties of an asymmetric mass distribution and vector field in generalized Einstein-aether (GEA) theory. As vector-field fluctuations are responsible in GEA for seeding baryonic structure formation, vector-field concentrations can exist independently of baryonic matter. Such concentrations would not be expected to be tied to baryonic matter except gravitationally, and so, like dark matter halos, would become separated from baryonic matter in interacting systems such as the bullet cluster. These vector-field concentrations cause metric deviations that affect weak lensing. Therefore, the distribution of weak lensing deviates from that which would be inferred from the luminous mass distribution, in a way that numerical calculations demonstrate can be consistent with observations. This suggests that MOND-inspired theories can reproduce weak lensing observations, but makes clear the price: the existence of a coherent large-scale fluctuation of a field(s) weakly tied to the baryonic matter, not completely dissimilar to a dark matter halo.

In this work, we consider time-dependent dark-energy star models, with an evolving parameter $\omega$ crossing the phantom divide $\omega =-1$. Once in the phantom regime, the null energy condition is violated, which physically implies that the negative radial pressure exceeds the energy density. Therefore, an enormous negative pressure in the center may, in principle, imply a topology change, consequently opening up a tunnel and converting the dark-energy star into a wormhole. The criteria for this topology change are discussed and, in particular, we consider a Casimir energy approach involving quasilocal energy difference calculations that may reflect or measure the occurrence of a topology change. We denote these exotic geometries consisting of dark-energy stars (in the phantom regime) and phantom wormholes as phantom stars. The final product of this topological change, namely, phantom wormholes, have far-reaching physical and cosmological implications, as in addition to being used for interstellar shortcuts, an absurdly advanced civilization may manipulate these geometries to induce closed timelike curves, consequently violating causality.

We use the conservation law of the stress-energy and spin tensors to study the motion of massive branelike objects in Riemann-Cartan geometry. The world-sheet equations and boundary conditions are obtained in a manifestly covariant form. In the particle case, the resultant worldline equations turn out to exhibit a novel spin-curvature coupling. In particular, the spin of a zero-size particle does not couple to the background curvature. In the string case, the world-sheet dynamics is studied for some special choices of spin and torsion. As a result, the known coupling to the Kalb-Ramond antisymmetric external field is obtained. Geometrically, the Kalb-Ramond field has been recognized as a part of the torsion itself, rather than the torsion potential.

Using recent polarimetric observations of the Crab Nebula in the hard X-ray band by INTEGRAL, we show that the absence of vacuum birefringence effects constrains $O(E/M)$ Lorentz violation in QED to the level $|\xi |<9\times {10}^{-10}$ at $3\sigma$ CL, tightening by more than 3 orders of magnitude previous constraints. We show that planned X-ray polarimeters have the potential to probe $|\xi |\sim {10}^{-16}$ by detecting polarization in active galaxies at red-shift $\sim 1$.

I visually explore the features of geodesic orbits in arbitrary stationary axisymmetric vacuum (SAV) spacetimes that are constructed from a complex Ernst potential. Some of the geometric features of integrable and chaotic orbits are highlighted. The geodesic problem for these SAV spacetimes is rewritten as a 2 degree of freedom problem and the connection between current ideas in dynamical systems and the study of two manifolds sought. The relationship between the Hamilton-Jacobi equations, canonical transformations, constants of motion, and Killing tensors are commented on. Wherever possible I illustrate the concepts by means of examples from general relativity. This investigation is designed to build the readers’ intuition about how integrability arises, and to summarize some of the known facts about 2 degree of freedom systems. Evidence is given, in the form of an orbit-crossing structure, that geodesics in SAV spacetimes might admit a fourth constant of motion that is quartic in momentum (by contrast with Kerr spacetime, where Carter’s fourth constant is quadratic).

This paper explores features of an idealized mathematical machine (algorithm) that would be capable of reconstructing the gravitational nature (the multipolar structure or spacetime metric) of a compact object, by observing gravitational radiation emitted by a small object that orbits and spirals into it. An outline is given of the mathematical developments that must be carried out in order to construct such a machine.