We construct an extension of $f(T)$ gravity with the inclusion of a nonminimal torsion-matter coupling in the action. The resulting theory is a novel gravitational modification, since it is different from both $f(T)$ gravity, as well as from the nonminimal curvature-matter-coupled theory. The cosmological application of this new theory proves to be very interesting. In particular, we obtain an effective dark energy sector whose equation-of-state parameter can be quintessence- or phantom-like, or exhibit the phantom-divide crossing, while for a large range of the model parameters the universe enters in a de Sitter, dark-energy-dominated, accelerating phase. Additionally, we can obtain early-time inflationary solutions too, and thus provide a unified description of the cosmological history.

In this work, we investigate the notion of time and unitarity in the vicinity of a bounce in quantum cosmology, that is, a turning point for the scale factor. Because WKB methods drastically fail near a turning point, the scale factor cannot play the role of time in such scenarios. We overcome this difficulty by studying the dynamics of matter transitions when using its conjugate momentum as a time. We find precise conditions so as to recover unitarity, and hence, a consistent notion of probability. We then compute transitions in a concrete example, extract the specific feature of a bounce and argue about the necessity of the conjugate momentum representation to go beyond the background field approximation. Our analysis is also equally relevant for a closed universe undergoing a recollapsing phase.

We model the supermassive Galactic center of the Milky Way Galaxy as a strongly naked singularity lens described by the Janis–Newman–Winicour metric. This metric has an ordinary mass and massless scalar charge parameters. For very accurate results, we use the Virbhadra–Ellis lens equation for computations. The Galactic center serving as a gravitational lens gives rise to four images: two images on the same side as the source and two images on the opposite side of the source from the optic axis. We compute positions and time delays of these images for many values of the angular source position. The time delays of primary images decrease with an increase in angular source position and are always negative. The time delays of the other three images are negative for a small angular source position; however, they increase with an increase in the angular source position. Such observations would support strongly naked singularity interpretation of the Galactic center, and would disprove the cosmic censorship hypothesis proposed by Roger Penrose as well as a weaker version by Virbhadra that allows the existence of weakly, but not marginally, and strongly naked singularities.

We propose an efficient method to compute the so-called residual phase that appears when performing Monte Carlo calculations on a Lefschetz thimble. The method is stochastic and its cost scales linearly with the physical volume, linearly with the number of stochastic estimators and quadratically with the length of the extra dimension along the gradient flow. This is a drastic improvement over previous estimates of the cost of computing the residual phase. We also report on basic tests of correctness and scaling of the code.

The hyperradial Schrödinger equation is considered with the Killingbeck potential which is a combination of harmonic and Cornell terms. Having calculated the wave function of a three-body baryonic system with the aid of the hyperspherical approach, we investigate the Isgur-Wise function for Lambda baryons and related concepts including the differential decay width, charge radius and the curvature parameters. In particular, the decay width of ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c$ transition is reported.

Some estimates for the transverse single spin asymmetry, $A_N$, in the inclusive processes $\ell p^{\uparrow }\to hX$, given in a previous paper, are expanded and compared with new experimental data. The predictions are based on the Sivers distributions and the Collins fragmentation functions which fit the azimuthal asymmetries measured in semi-inclusive deep inelastic scattering (SIDIS) processes ($\ell p^{\uparrow }\to {\ell }^{\prime }hX$). The factorization in terms of transverse momentum dependent distribution and fragmentation functions (TMD factorization)—i.e. the theoretical framework in which SIDIS azimuthal asymmetries are analyzed—is assumed to hold also for the inclusive process $\ell p\to hX$ at large $P_T$. The values of $A_N$ thus obtained agree in sign and shape with the data. Some predictions are given for future experiments.

The hyperon vector form factors at zero momentum transfer, $f_1(0)$, play an important role in a precise determination of the Cabibbo-Kobayashi-Maskawa matrix element $V_{us}$. Recent studies based on lattice chromodynamics (LQCD) simulations and covariant baryon chiral perturbation theory yield contradicting results. In this work, we study chiral extrapolation of and finite-volume corrections to the latest $n_f=2+1$ LQCD simulations. Our results show that finite-volume corrections are relatively small and can be safely ignored at the present LQCD setup of $m_{\pi }L=4.6$, but chiral extrapolation needs to be performed more carefully. Nevertheless, the discrepancy remains, and further studies are needed to fully understand it.

We outline a systematic approach to the determination of the standard model-like Higgs boson total width and measurable coupling parameters in a model-independent manner at the International Linear Collider and illustrate the complementarity for operating it at 250 GeV near the $Zh$ threshold and at 500 GeV and 1 TeV utilizing the $WW$, $ZZ$ fusion processes. We perform detailed simulations for an important contributing channel to the coupling determination and for invisible decays. Without model assumptions, and combining the information for the coupling ratios from the LHC, the total width can be determined to an accuracy of about 6%, and the couplings for the observable channels can be measured to the (3–5)% level at 250 GeV, reaching (1–3)% level including the 500 GeV results, with further improvements possible with a 1 TeV run. The best precision for the branching fraction measurement of the Higgs to invisible modes can be reached at 0.5%–0.7% around the $Zh$ threshold. Further studies from $ZZ$ fusion at higher energies may provide significant improvement for the measurements. With modest theory assumptions, the width and coupling determinations can be further improved to the percent or subpercent level.

We consider hard three-loop nonlogarithmic corrections of order $m{\alpha }^7$ to hyperfine splitting in positronium. All these contributions are generated by the graphs with photon and/or electron loop radiative insertions in the two-photon exchange diagrams. We calculate contributions of six gauge-invariant sets of diagrams. The total result for all these diagrams is $\mathrm{\Delta }E=-1.2917(1)m{\alpha }^7/{\pi }^3=-5.672\mathrm{kHz}$.

We consider type IIA brane configurations, similar to those that realize $SO(2N)$ supersymmetric QCD, that include orientifold planes and antibranes. Such brane configurations lead to $Sp(2N)$ field theories that become supersymmetric in the large-$N$ limit and break supersymmetry upon the inclusion of $1/N$ corrections. We argue that this class of field theories admits Seiberg duality and interpret the potential between branes and orientifolds as field theory phenomena. In particular, we find in the magnetic theory a meson potential that leads to dynamical symmetry breaking and a meson condensate similar to the anticipated quark condensate in QCD.

In symmetry-based approaches to black hole entropy, we calculate the central charge of the Virasoro algebra in the first order formulation of gravity for both Palatini and Holst actions. In these calculations, we make use of the near-horizon extremal Kerr metric and the Kerr/conformal field theory correspondence. For the Palatini action the results obtained in the second order formulation are reproduced. We also argue that the Holst term does not contribute to the charge algebra no matter what geometry/boundary conditions one is considering.

By applying scaling transformations to distance and time, we obtain the first post-Newtonian equations of motion for a relativistic circular restricted three-body problem, where the Newtonian terms do not depend on the separation of a parent binary, though the post-Newtonian terms do. The post-Newtonian contributions consist of the relativistic effects from the circular orbital frequencies between the primaries and those from the primaries to a third body. When the former post-Newtonian contribution and the nonrelativistic terms are considered, the post-Newtonian dynamics are qualitatively different from the Newtonian dynamics if the separation between the two primaries is insufficiently large. When the latter post-Newtonian contribution is also included, some orbits become unstable. By scanning the dependence of the dynamics on the separation with fast Lyapunov indicators, the separation is classified into three domains for dynamically unstable, bounded chaotic, and bounded regular dynamics.

We consider trapped inflation in a higher dimensional field space: particle production at a dense distribution of extra species points leads to a terminal velocity at which inflation can be driven in steep potentials. We compute an additional, nearly scale invariant contribution to the power spectrum, caused by backscattering of the continuously produced particles. Since this contribution has a blue tilt, it has to be subdominant, leading to an upper bound on the coupling constant between the inflatons and the extra species particles. The remaining allowed parameter space is narrow.

The cosmological dynamics of gravitational clustering satisfies an approximate invariance with respect to the cosmological parameters that is often used to simplify analytical computations. We describe how this approximate symmetry gives rise to angular-averaged consistency relations for the matter density correlations. This allows one to write the ($\ell +n$) density correlation, with $\ell$ large-scale linear wave numbers that are integrated over angles, and $n$ fixed small-scale nonlinear wave numbers, in terms of the small-scale $n$-point density correlation and $\ell$ prefactors that involve the linear power spectra at the large-scale wave numbers. These relations, which do not vanish for equal-time statistics, go beyond the already known kinematic consistency relations. They could be used to detect primordial non-Gaussianities, modifications of gravity, limitations of galaxy biasing schemes, or to help design analytical models of gravitational clustering.

We make a comprehensive analysis of the phenomenology in the minimal version of the cascade seesaw mechanism for tiny neutrino masses. The seesaw mechanism induces, at tree level, a neutrino mass operator at dimension nine by introducing a quadruple scalar $\mathrm{\Phi }$ of hypercharge unity and a quintuple fermion $\mathrm{\Sigma }$ of hypercharge zero. We work in a framework that handles the complicated Yukawa couplings without losing generality. All mixing matrices are essentially expressed in terms of the vacuum expectation value of the quadruple scalar $v_{\mathrm{\Phi }}$, a free complex parameter $t$, and known neutrino parameters. We show that the low-energy lepton-flavor-violating transitions of the charged leptons set strong constraints on the free parameters. The constraints have a significant impact on collider physics and are incorporated in our signal analysis at the LHC. We investigate the signatures of new particles by surveying potentially important channels. We find that the $4j2{\ell }^{\pm }$ signal is the most important for the detection of scalars, and the $2{\ell }^{\pm }2{\ell }^{\mp }2j$, $3{\ell }^{\pm }{\ell }^{\mp }2j$, and $3{\ell }^{\pm }2{\ell }^{\mp }+\cancel{E_T}$ signals are quite promising for the fermions.

We explore the possibility of employing $e^{+}{e}^{-}$ colliders to probe the scotogenic model, in which neutrinos get mass radiatively via one-loop interactions involving dark matter. Assuming the lightest one of the new particles in the model to be fermionic cold dark matter and taking into account various constraints, including those from LHC Higgs experiments, we show that LEP II data on $e^{+}{e}^{-}$ scattering into a pair of charged leptons plus missing energy can place significant extra restrictions on the parameter space containing sufficiently low masses of the charged scalars in the model. On the other hand, LEP II data on $e^{+}{e}^{-}$ collisions into a photon plus missing energy do not yield strong constraints. The allowed parameter space can still accommodate Higgs exotic decays into the nonstandard particles and thus is testable at the LHC. We also consider using future measurements of these two types of $e^{+}{e}^{-}$ scattering at the International Linear Collider to examine the scenario of interest further and find that they can provide complementary information about it, whether or not they reveal scotogenic effects.

We propose a new channel of the neutrinoless double beta decay, based on the fact that in the presence of an external nonuniform magnetic field, the transition between neutrino and antineutrino can take place through the induced neutrino magnetic moment. We calculate the analog of the effective neutrino mass for this channel and show that, for certain values of the external magnetic field, a resonant enhancement can be obtained.

The hemispherical power asymmetry observed by Planck and WMAP can be interpreted as due to a spatially-varying and scale-dependent component of the adiabatic power spectrum. We derive general constraints on the magnitude and scale-dependence of a component with a dipole spatial variation. The spectral index and the running of the spectral index can be significantly shifted from their inflation model values, resulting in a smaller spectral index and a more positive running. A key prediction is a hemispherical asymmetry of the spectral index and of its running. Measurement of these asymmetries can test the structure of the perturbation responsible for the cosmic microwave background power asymmetry.

$O(n)\times O(m)$ symmetric Landau-Ginzburg models in $d=3$ dimensions possess a rich structure of the renormalization group, which offers a theoretical prediction of the phase diagram in frustrated spin models with noncollinear order. Depending on $n$ and $m$, they may show chiral/antichiral/Heisenberg/Gaussian fixed points within the same universality class. We approach all the fixed points in the conformal bootstrap program by examining the bound on the conformal dimensions for scalar operators as well as nonconserved current operators with consistency cross-checks. For large $n/m$, we show strong evidence for the existence of four fixed points by comparing the operator spectrum obtained from the conformal bootstrap program with that from the large-$n/m$ analysis. We propose a novel nonperturbative approach to the determination of the conformal window in these models based on the conformal bootstrap program. From our numerical results, we predict that for $m=3$, $n=7\sim 8$ is the edge of the conformal window for the antichiral fixed points.

We define a modified dimensional-regularization technique that overcomes several difficulties of the ordinary technique, and is specially designed to work efficiently in chiral and parity violating quantum field theories, in arbitrary dimensions greater than 2. When the dimension of spacetime is continued to complex values, spinors, vectors and tensors keep the components they have in the physical dimension; therefore, the $\gamma$ matrices are the standard ones. Propagators are regularized with the help of evanescent higher-derivative kinetic terms, which are of the Majorana type in the case of chiral fermions. If the new terms are organized in a clever way, weighted power counting provides an efficient control on the renormalization of the theory, and allows us to show that the resulting chiral dimensional regularization is consistent to all orders. The new technique considerably simplifies the proofs of properties that hold to all orders, and makes them suitable to be generalized to wider classes of models. Typical examples are the renormalizability of chiral gauge theories and the Adler-Bardeen theorem. The difficulty of explicit computations, on the other hand, may increase.