A new way to write the massive scalar and fermion propagators on a background of a weak gauge field is presented. They are written in a form that is manifestly gauge covariant up to several additional terms that can be written as boundary terms in momentum space. These additional terms violate Ward-Takahashi identities and need to be renormalized by appropriate counterterms if the complete theory is to be gauge covariant. This form makes it possible to calculate many amplitudes in a manifestly gauge-covariant way (at the same time reducing the number of Feynman diagrams). It also allows one to express some counterterms in a way independent of the regularization scheme and provides an easy way to derive the anomalous term affecting the chiral current conservation.

We study the canonical realization of Bondi-Metzner-Sacks symmetry for a massive scalar field introduced by Longhi and Materassi [J. Math. Phys. 40, 480 (1999)]. We construct an invariant scalar product for the generalized momenta. As a consequence we introduce a quadratic Casimir with the supertranslations.

We address the study of gauge invariance in the Standard Model extension which encompasses all Lorentz-violating terms originated by spontaneous symmetry breaking at the Planck scale. In particular, we fully evaluate Ward identities involving two- and three-point functions and derive the conditions which assure gauge invariance of the electromagnetic sector of the Standard Model extension at one loop. We show that momentum routing invariance is sufficient to fix arbitrary and regularization dependent parameters intrinsic to perturbation theory in the diagrams involved. A scheme which judiciously collects finite but undetermined quantum corrections is employed, a particularly subtle issue in the presence of ${\gamma }_5$ matrices.

We investigate the topological properties of the $SU(3)$ pure gauge theory by performing numerical simulations at imaginary values of the $\theta$ parameter. By monitoring the dependence of various cumulants of the topological charge distribution on the imaginary part of $\theta$ and exploiting analytic continuation, we determine the free energy density up to the sixth order in $\theta$, $f(\theta ,T)=f(0,T)+\frac{1}{2}\chi (T){\theta }^2(1+b_2(T){\theta }^2+b_4(T){\theta }^4+O({\theta }^6))$. That permits us to achieve determinations with improved accuracy, in particular for the higher-order terms, with control over the continuum and the infinite-volume extrapolations. We obtain $b_2=-0.0216(15)$ and $|b_4|\lesssim 4\times {10}^{-4}$.

Using a fundamental discrete symmetry, ${\mathbf{Z}}_N$, we construct a two-axion model with the QCD axion solving the strong-$CP$ problem, and an ultralight axion (ULA) with $m_{\mathrm{ULA}}\approx 10^{-22}\mathrm{eV}$ providing the dominant form of dark matter (DM). The ULA is light enough to be detectable in cosmology from its imprints on structure formation, and may resolve the small-scale problems of cold DM. The necessary relative DM abundances occur without fine-tuning in constructions with decay constants $f_{\mathrm{ULA}}\sim {10}^{17}\mathrm{GeV}$, and $f_{\mathrm{QCD}}\sim {10}^{11}\mathrm{GeV}$. An example model achieving this has $N=24$, and we construct a range of other possibilities. We compute the ULA couplings to the standard model, and discuss prospects for direct detection. The QCD axion may be detectable in standard experiments through the $\overrightarrow{E}·\overrightarrow{B}$ and $G\tilde{G}$ couplings. In the simplest models, however, the ULA has identically zero coupling to both $G\tilde{G}$ of QCD and $\overrightarrow{E}·\overrightarrow{B}$ of electromagnetism due to vanishing electromagnetic and color anomalies. The ULA couples to fermions with strength $g\propto 1/f_{\mathrm{ULA}}$. This coupling causes spin precession of nucleons and electrons with respect to the DM wind with period $t\sim$ months. Current limits do not exclude the predicted coupling strength, and our model is within reach of the CASPEr-Wind experiment, using nuclear magnetic resonance.

We compute the form factors for the $B\to K{l}^{+}{l}^{-}$ semileptonic decay process in lattice QCD using gauge-field ensembles with $2+1$ flavors of sea quark, generated by the MILC Collaboration. The ensembles span lattice spacings from 0.12 to 0.045 fm and have multiple sea-quark masses to help control the chiral extrapolation. The asqtad improved staggered action is used for the light valence and sea quarks, and the clover action with the Fermilab interpretation is used for the heavy $b$ quark. We present results for the form factors $f_{+}(q^2)$, $f_0(q^2)$, and $f_T(q^2)$, where $q^2$ is the momentum transfer, together with a comprehensive examination of systematic errors. Lattice QCD determines the form factors for a limited range of $q^2$, and we use the model-independent $z$ expansion to cover the whole kinematically allowed range. We present our final form-factor results as coefficients of the $z$ expansion and the correlations between them, where the errors on the coefficients include statistical and all systematic uncertainties. We use this complete description of the form factors to test QCD predictions of the form factors at high and low $q^2$.

We analyze the late-time decay of scalar perturbations in extremal Reissner-Nordstrom spacetime. We consider individual spherical-harmonic modes $l$ of a test massless scalar field, restricting our attention to the initial data of compact support, with generic regular behavior across the horizon. We obtain a decay rate $\propto t^{-(2l+3)}$ (just like in Schwarzschild) for incident waves scattered by the black hole. However, for waves originating at the horizon’s neighborhood, we obtain a slightly slower decay, $\propto t^{-(2l+2)}$. We discuss relations to previous works.

We study flat Friedmann-Lemaître-Robertson-Walker cosmological models for a scalar field coupled nonminimally to teleparallel gravity with generic coupling and potential functions. The goal in this paper is to determine the conditions under which cosmological evolution tends to the limit where the variation of the gravitational “constant” ceases and the system evolves close to general relativity (GR). These conditions can be read off from the approximate analytical solutions describing the process in matter and potential domination eras. Only those models where the GR limit exists and is an attractor can be considered viable. We expect the results to hold in the original “pure tetrad” formulation as well as in the recently suggested covariant formulation of the teleparallel theory. In the former case the GR attractor simultaneously provides a mechanism for how cosmological evolution suppresses the problematic degrees of freedom stemming from the lack of local Lorentz invariance.

We address the issues related to the presence of the quantum potential term in a BEC on the observable analogue gravity systems. We show that the quantum potential term apparently gives rise to massive scalar excitations of length scales of the order $\mathcal{O}(1/\xi )$ in the lower dimensional space. Since, in “analogue models”, there is a window for experimental observations generally in ($2+1$) or even lower dimensional space, one has to take proper account of the presence of these massive excitations to interpret the results.

In this paper we explore the advantage of using the Kerr-Schild Ansatz in the search for analytic configurations to bigravity. It turns out that it plays a crucial role by providing means to straightforwardly calculate the square root matrix encoding the interaction terms between both gravities. In this spirit, we rederive the Babichev-Fabbri family of asymptotically flat rotating black holes with the aid of an emerging circularity theorem. Taking into account that the interaction terms contain by default two cosmological constants, we repeat our approach starting from the more natural seeds for the Kerr-Schild Ansatz in this context: the (A)dS spacetimes. As a result, we show that a couple of Kerr–(A)dS black holes constitute an exact solution to ghost-free bigravity. Similar to the asymptotically flat case, these black holes share the same angular momentum and (A)dS radius, but their masses are not constrained to be equal.

Cosmic microwave background lensing has become a new cosmological probe, carrying rich information on the matter power spectrum and distances over the redshift range $z\approx 1-4$. We investigate the role of scale dependent new physics, such as from modified gravity, neutrino mass, and cold (low sound speed) dark energy, and its signature on CMB lensing. The distinction between different scale dependences, and the different redshift dependent weighting of the matter power spectrum entering into CMB lensing and other power spectra, imply that CMB lensing can probe simultaneously a diverse range of physics. We highlight the role of arcminute resolution polarization experiments for distinguishing between physical effects.

We present the first cosmological measurement derived from a galaxy density field subject to a “clipping” transformation. By enforcing an upper bound on the galaxy number density field in the galaxy and mass assembly survey (GAMA), contributions from the nonlinear processes of virialization and galaxy bias are greatly reduced. This leads to a galaxy power spectrum which is easier to model, without calibration from numerical simulations. We develop a theoretical model for the power spectrum of a clipped field in redshift space, which is exact for the case of anisotropic Gaussian fields. Clipping is found to extend the applicability of the conventional Kaiser prescription by more than a factor of 3 in wave numbers, or a factor of 30 in terms of the number of Fourier modes. By modeling the galaxy power spectrum on scales $k<0.3h{\mathrm{Mpc}}^{-1}$ and density fluctuations ${\delta }_g<4$ we measure the normalized growth rate $f{\sigma }_8(z=0.18)=0.29\pm 0.10$.

We show that observation of the time-dependent effect of microlensing of relativistically broadened emission lines (such as e.g. the Fe $\mathrm{K}\alpha$ line in x rays) in strongly lensed quasars could provide data on celestial mechanics of circular orbits in the direct vicinity of the horizon of supermassive black holes. This information can be extracted from the observation of evolution of the red/blue edge of the magnified line just before and just after the period of crossing of the innermost stable circular orbit by the microlensing caustic. The functional form of this evolution is insensitive to numerous astrophysical parameters of the accreting black hole and of the microlensing caustics network system (as opposed to the evolution of the full line spectrum). Measurement of the temporal evolution of the red/blue edge could provide a precision measurement of the radial dependence of the gravitational redshift and of velocity of the circular orbits, down to the innermost stable circular orbit. These measurements could be used to discriminate between general relativity and alternative models of the relativistic gravity in which the dynamics of photons and massive bodies orbiting the gravitating center is different from that of the geodesics in the Schwarzschild or Kerr space-times.

We describe an improved Michelson-Morley-type laser apparatus for highly sensitive tests of Lorentz invariance in the electron and photon sectors. The realization of an ultrastable rotation table reduced by more than one order systematic effects occurring with the rotation period. We also reduced by one order the noise level, resulting in integration times smaller by more than one order. Under reasonable assumptions, we determine five coefficients of the standard model extension test theory, with uncertainties similar to the previous best experiments, but with a 30 times shorter data acquisition time span. Four coefficients are consistent with zero at the $(4–8)\times {10}^{-18}$ level, while one, $({\tilde{\kappa }}_{e-}{)}^{ZZ}\simeq 5\times {10}^{-17}$, appears to be caused by unidentified systematic effects. In addition, the apparatus’ performance leads to a limit for the strength of (hypothetical) space-time fluctuations improved by a factor of 3.7.

We present a new solution of relativistic hydrodynamics in $1+3$ dimensions which depends on both the transverse coordinate and rapidity. At early times the flow expands dominantly longitudinally in a nonboost-invariant manner, and at late times it expands nearly spherically. These two regimes are shown to be related by symmetry. The effect of viscosity is also discussed.

We study the lepton flavor violating process, $e+T\to \tau +T^{\prime }$, at a few GeV. This process can be studied by experiments directing GeV scale electron or positron beams on internal or fixed targets. We study the effects of some low energy lepton flavor violating interactions on this process. We study the sensitivities of this process on these low energy lepton flavor violating interactions and compare them to the sensitivities of lepton flavor violating $\tau$ decay processes. Comparing with $\tau$ decay processes, this process provides another way to study the lepton flavor violating effects with $e-\tau$ conversion and it can be searched for in facilities with GeV scale electron or positron beams which are available in a number of laboratories in the world.

Abstract The Lee-Wick Standard Model is a highly constrained model which solves the gauge hierarchy problem at the expense of including states with negative norm. It appears to be macroscopically causal and consistent. This model is extended by considering the two-Higgs doublet extension of the Lee-Wick model. Rewriting the Lagrangian using auxiliary fields introduces two additional doublets of Lee-Wick partners. The model is highly constrained, with only one or two additional parameters beyond that of the usual two-Higgs doublet model, and yet there are four doublets. Mass relations are established by diagonalizing the mass matrices and further constraints are established by studying results from $B\to \tau \nu$, neutral $B$-meson mixing, and $B\to X_s\gamma$. The prospects of detecting evidence for this model at the LHC are discussed.

We consider models of supersymmetry that can incorporate sizeable mixing between different generations of sfermions. While the mixing is constrained by the nonobservation of various flavor-changing neutral current processes, there exist regions of the SUSY parameter space where the effects of such mixing can be probed at colliders. In this work, we explore this possibility by focusing on the slepton sector. The sleptons are produced through cascade decays in direct neutralino-chargino (${\chi }_2^0{\chi }_1^{\pm }$) pair production at the Large Hadron Collider (LHC). The final state is characterized by three leptons and missing energy. We probe the lepton-flavor-violating (LFV) vertex arising in ${\chi }_2^0$ decay by identifying a distinct and unambiguous combination of the trilepton final state containing a lepton pair with same flavor and same sign (SFSS) in addition to a pair with opposite flavor and opposite sign (OFOS). This combination of a trilepton final state containing both OFOS and SFSS pairs can not only suppress the SM background but also differentiate the flavor-violating decays of ${\chi }_2^0$ from its corresponding flavor-conserving decays. We present results showing the sensitivity of lepton-flavor-violating parameters for a wide range of slepton and chargino-neutralino masses. In addition, we also illustrate signal significance for various points in the parameter space, taking into account background contributions assuming two luminosity options (100 and $1000{\mathrm{fb}}^{-1}$) for the LHC run 2 experiment at $\sqrt{s}=14\mathrm{TeV}$.

Recently, the LHC collaborations, ATLAS and CMS, have announced an excess in the diphoton channel with local significance of about $3\sigma$ around an invariant mass distribution of $\sim 750\mathrm{GeV}$, after analyzing new data collected at center-of-mass energies of $\sqrt{s}=13\mathrm{TeV}$. We present a possible physical interpretation of such a signature, within the framework of a minimal UV-complete model with a massive singlet pseudoscalar state $a$ that couples to a new TeV-scale colored vectorlike fermion $F$, whose hypercharge quantum number is a non-zero integer. The pseudo-scalar state $a$ might be a heavy pseudo-Goldstone boson, such as a heavy axion, which decays into two photons and whose mass lies around the excess region. The mass of the $CP$-odd state $a$ and its coupling to $F$ may be due to nonperturbative effects, which can break the original Goldstone shift symmetry dynamically. The possible role that the heavy axion $a$ can play in the radiative generation of a seesaw Majorana scale and in the solution to the so-called strong $CP$ problem is briefly discussed.

We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal. We consider a general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints. The case where dark matter has a self-interaction strength $⟨{\sigma }_V⟩/m_{\psi }\sim 0.1–1{\mathrm{cm}}^2/\mathrm{g}$ is strongly constrained, in particular by the big bang nucleosynthesis. We show that these constraints can be alleviated by introducing a new light sterile neutrino $N$. The allowed region for the extended model consists of two triangles as a function of the mass $m_N$ and a sufficiently small sterile-active neutrino mixing angle $\sin \theta <0.007$: first $10(\sin \theta {)}^{-2/5}\mathrm{MeV}\lesssim m_N\lesssim 1\mathrm{GeV}$ and second $15(\sin \theta {)}^{-2/5}\mathrm{keV}\lesssim m_N\lesssim 1\mathrm{MeV}$.