The exclusive semileptonic decay $B\to \pi \ell \nu$ is a key process for the determination of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$ from the comparison of experimental rates as a function of $q^2$ with theoretically determined form factors. The sensitivity of the form factors to the $u/d$ quark mass has meant significant systematic uncertainties in lattice QCD calculations at unphysically heavy pion masses. Here, we give the first lattice QCD calculations of this process for $u/d$ quark masses going down to their physical values, calculating the $f_0$ form factor at zero recoil to 3%. We are able to resolve a long-standing controversy by showing that the soft-pion theorem result $f_0(q_{\max }^2)=f_B/f_{\pi }$ does hold as $m_{\pi }\to 0$. We use the highly improved staggered quark formalism for the light quarks and show that staggered chiral perturbation theory for the $m_{\pi }$ dependence is almost identical to continuum chiral perturbation theory for $f_0$, $f_B$, and $f_{\pi }$. We also give results for other processes such as $B_s\to K\ell \nu$.

We investigate the neutral hidden charm pentaquark states $P_c^0(4380)$ and $P_c^0(4450)$ in the ${\pi }^{-}p\to J/\psi n$ reaction within an effective Lagrangian approach. The background contributions for the process mainly come from $t$-channel $\pi$ and $\rho$ meson exchanges. The contributions of the $P_c^0(4380)$ and $P_c^0(4450)$ states give clear peak structures in the magnitude of $1\mu \mathrm{b}$ at center-of-mass energies 4.38 GeV and 4.45 GeV in the total cross sections. Hence, this reaction may provide a new platform to search for neutral $P_c$ states. It is expected that our estimated total cross sections, together with the angular distributions, can be tested by future experiments at J-PARC.

We present precise theoretical predictions for the absolute branching fractions of ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\ell }^{+}{\nu }_{\ell }(\ell =e,\mu )$ decays in the covariant confined quark model. This study is motivated by two recent and accurate measurements of the absolute branching fractions of ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{e}^{+}{\nu }_e$ by the Belle Collaboration at the KEKB and by the BESIII Collaboration at the BEPCII. Our predictions for the branching fractions are consistent with both experimental results. We also provide detailed numerical results for differential decay distributions and polarization observables.

We match the nonrelativistic quark model, with both flavor-dependent and flavor-independent effective quark-quark interactions, to the spin-flavor operator basis of the $1/N_c$ expansion for the $L=1$ nonstrange baryons. We obtain analytic expressions for the coefficients of the $1/N_c$ operators in terms of radial integrals that depend on the shape and relative strength of the spin-spin, spin-orbit and tensor interactions of the model, which are left unspecified. We obtain several new, parameter-free relations between the seven masses and the two mixing angles that can discriminate between different spin-flavor structures of the effective quark-quark interaction. We discuss in detail how a general parametrization of the mass matrix depends on the mixing angles and is constrained by the assumptions on the effective quark-quark interaction. We find that, within the present experimental uncertainties, consistency with the best values of the mixing angles as determined by a recent global fit to masses and decays does not exclude any of the two most extreme possibilities of flavor-dependent (-independent) quark-quark interactions, as generated by meson (gluon) exchange interactions.

The Majorana neutrino in the type-I seesaw and the pseudo-Dirac neutrinos in the inverse seesaw can have sizable mixings with the light neutrinos in the standard model, through which the heavy neutrinos can be produced at the LHC. In producing the heavy neutrinos, we study a variety of initial states such as quark-quark, quark-gluon and gluon-gluon as well as photon mediated processes. For the Majorana heavy neutrino production, we consider a same-sign dilepton plus dijet as the signal events. Using the recent ATLAS and CMS data at $\sqrt{s}=8\mathrm{TeV}$ with 20.3 and $19.7{\mathrm{fb}}^{-1}$ luminosities, respectively, we obtain direct upper bounds on the light-heavy neutrino mixing angles. For the pseudo-Dirac heavy neutrino production we consider the final sate with a trilepton plus missing energy as the signal events. Using the recent anomalous multilepton search by CMS at $\sqrt{s}=8\mathrm{TeV}$ with $19.5{\mathrm{fb}}^{-1}$ luminosity, we obtain upper bounds on the mixing angles. Taking the varieties of initial states into account, the previously obtained upper bounds on the mixing angles have been improved. We scale our results at the 8 TeV LHC to obtain a prospective search reach at the 14 TeV LHC with high luminosities.

Mono-$X$ signatures are a powerful collider probe of the nature of dark matter. We show that mono-Higgs and mono-$Z$ may be key signatures of pseudoscalar portal interactions between dark matter and the standard model. We demonstrate this using a simple renormalizable version of the portal, with a two-Higgs-doublet model as an electroweak symmetry breaking sector. Mono-$Z$ and mono-Higgs signatures in this scenario are of resonant type, which constitutes a novel type of dark matter signature at the LHC.

We study the single site lattice gauge theory of $SU(N)$ coupled to one Dirac flavor of fermion in the adjoint representation. We utilize Möbius fermions for this study, and accelerate the calculation with graphics processing units. Our Monte Carlo simulations indicate that for sufficiently large inverse ’t Hooft coupling $b=1/g^{2}N$, and for $N\le 10$ the distribution of traced Polyakov loops has “fingers” that extend from the origin. However, in the massless case the distribution of eigenvalues of the untraced Polyakov loop becomes uniform at large $N$, indicating preservation of center symmetry in the thermodynamic limit. By contrast, for a large mass and large $b$, the distribution is highly nonuniform in the same limit, indicating spontaneous center symmetry breaking. These conclusions are confirmed by comparing to the quenched case, as well as by examining another observable based on the average value of the modulus of the traced Polyakov loop. The result of this investigation is that with massless adjoint fermions center symmetry is stabilized and the Eguchi-Kawai reduction should be successful; this is in agreement with most other studies.

We show that the standard model vacuum can be stabilized if all particle propagators are nonminimally coupled to gravity. This is due to a Higgs-background dependent redefinition of the standard model fields: in terms of canonical variables and in the large Higgs field limit, the quantum fluctuations of the redefined fields are suppressed by the Higgs background. Thus, in this regime, quantum corrections to the tree-level electroweak potential are negligible. Finally, we show that in this framework the Higgs boson can be responsible for inflation. Due to a numerical coincidence that originates from the CMB data, inflation can happen if the Higgs boson mass, the top mass, and the QCD coupling lie in a region of the parameter space approximately equivalent than the one allowing for electroweak vacuum stability in the standard Model. We find some (small) regions in the standard model parameter space in which the new interaction “rescues” the electroweak vacuum, which would not be stable in the standard model.

Sterile neutrinos in the electronvolt mass range are hinted at by a number of terrestrial neutrino experiments. However, such neutrinos are highly incompatible with data from the cosmic microwave background and large scale structure. This paper discusses how charging sterile neutrinos under a new pseudoscalar interaction can reconcile eV sterile neutrinos with cosmological data. We show that this model provides a fit to all available data which is way better than the standard $\mathrm{\Lambda }$ cold dark matter model with one additional fully thermalized sterile neutrino. In particular it also prefers a value of the Hubble parameter much closer to the locally measured value.

This paper investigates a particular type of wormhole. The wormhole solutions studied are obtained by sewing together two static, spherically symmeric, charged black-hole metrics at their horizons. The charged wormholes are in a background Kalb-Ramond field, which is the source of the necessary tension in the gravitational field. The metric-tensor elements are studied by numerically solving Einstein’s equations with stress-energy-tensor elements given by the combination of static electric and Kalb-Ramond fields. For a certain range of electric charge the tension is positive away from the wormhole throat, but the tension is negative near the throat, making it nontraversable. The wormholes are found to be quasistable against decay via gravitational instanton tunneling.

In the work of Hohmann et al. [Phys. Rev. D 88, 084054 (2013)], the authors worked out the parametrized post-Newtonian (PPN) parameters $\gamma$ and $\beta$ of a scalar-tensor theory with an arbitrary coupling function and a generic potential, and they found that these two PPN parameters depend on the radial distance $r$ from the Sun, $\gamma (r)$ and $\beta (r)$. Based on the assumption that measurements on the PPN parameters can be characterized by the shortest distance to the Sun, the authors obtained their best constraints on the model parameters of the scalar-tenor theory by light deflection observation and the Cassini tracking experiment. However, as the authors stated, this approach might not be rigorous. In the present work, we physically model astronomical observations and physical experiments by calculating the null and timelike geodesics in the scalar-tensor theory. We show that, contrary to the results in the previous work, the light deflection and the Cassini tracking cannot distinguish the scalar-tensor theory from general relativity. We also investigate the additional advances in perihelia caused by the largest correction of the scalar field on the Newtonian potential. Since this correction has a Yukawa-like form, we obtain very much improved lower bounds on the model parameters by using current upper limits on the Yukawa parameters.

We continue our series of studies of high-energy collisions of black holes investigating unequal-mass, boosted head-on collisions in four dimensions. We show that the fraction of the center-of-mass energy radiated as gravitational waves becomes independent of mass ratio and approximately equal to 13% at large energies. We support this conclusion with calculations using black hole perturbation theory and Smarr’s zero-frequency limit approximation. These results lend strong support to the conjecture that the detailed structure of the colliding objects is irrelevant at high energies.

We analyze time evolution of a spherically symmetric collapsing matter from a point of view that black holes evaporate by nature. We first consider a spherical thin shell that falls in the metric of an evaporating Schwarzschild black hole of which the radius $a(t)$ decreases in time. The important point is that the shell can never reach $a(t)$ but it approaches $a(t)-a(t)\frac{\mathrm{d}a(t)}{\mathrm{d}t}$. This situation holds at any radius because the motion of a shell in a spherically symmetric system is not affected by the outside. In this way, we find that the collapsing matter evaporates without forming a horizon. Nevertheless, a Hawking-like radiation is created in the metric, and the object looks the same as a conventional black hole from the outside. We then discuss how the information of the matter is recovered. We also consider a black hole that is adiabatically grown in the heat bath and obtain the interior metric. We show that it is the self-consistent solution of $G_{\mu \nu }=8\pi G⟨T_{\mu \nu }⟩$ and that the four-dimensional Weyl anomaly induces the radiation and a strong angular pressure. Finally, we analyze the internal structures of the charged and the slowly rotating black holes.

We present a method for solving the first-order Einstein field equations in a post-Newtonian (PN) expansion. Our calculations generalize the work of Bini and Damour and subsequently Kavanagh et al. to consider eccentric orbits on a Schwarzschild background. We derive expressions for the retarded metric perturbation at the location of the particle for all $\ell$-modes. We find that, despite first appearances, the Regge-Wheeler gauge metric perturbation is $C^0$ at the particle for all $\ell$. As a first use of our solutions, we compute the gauge-invariant quantity $⟨U⟩$ through 4PN while simultaneously expanding in eccentricity through $e^{10}$. By anticipating the $e\to 1$ singular behavior at each PN order, we greatly improve the accuracy of our results for large $e$. We use $⟨U⟩$ to find 4PN contributions to the effective one body potential $\widehat{Q}$ through $e^{10}$ and at linear order in the mass ratio.

Scalar-tensor (ST) theories of gravity are natural phenomenological extensions to general relativity. Although these theories are severely constrained both by solar system experiments and by binary pulsar observations, a large set of ST families remain consistent with these observations. Recent work has suggested probing the unconstrained region of the parameter space of ST theories based on the stability properties of highly compact neutron stars. Here, the dynamical evolution of very compact stars in a fully nonlinear code demonstrates that the stars do become unstable and that the instability, in some cases, drives the stars to collapse. We discuss the implications of these results in light of recent observations of the most massive neutron star yet observed. In particular, such observations suggest that such a star would be subject to the instability for a certain regime; its existence therefore supports a bound on the ST parameter space.

We show that the dilaton Melvin-Schwarzschild black hole solution is the only asymptotically dilaton Melvin static axisymmetric black hole solution of Einstein-Maxwell dilaton equations of motion.

We investigate all feasible mathematical representations of disformal transformations on a space-time metric according to the action of a linear operator upon the manifold’s tangent and cotangent bundles. The geometric, algebraic, and group structures of this operator and their interfaces are analyzed in detail. Then, we scrutinize a possible physical application, providing a new covariant formalism for a phenomenological approach to quantum gravity known as rainbow gravity.

An approach to testing theories describing a multiverse, that has gained interest of late, involves comparing theory-generated probability distributions over observables with their experimentally measured values. It is likely that such distributions, were we indeed able to calculate them unambiguously, will assign low probabilities to any such experimental measurements. An alternative to thereby rejecting these theories, is to conditionalize the distributions involved by restricting attention to domains of the multiverse in which we might arise. In order to elicit a crisp prediction, however, one needs to make a further assumption about how typical we are of the chosen domains. In this paper, we investigate interactions between the spectra of available assumptions regarding both conditionalization and typicality, and draw out the effects of these interactions in a concrete setting; namely, on predictions of the total number of species that contribute significantly to dark matter. In particular, for each conditionalization scheme studied, we analyze how correlations between densities of different dark matter species affect the prediction, and explicate the effects of assumptions regarding typicality. We find that the effects of correlations can depend on the conditionalization scheme, and that in each case atypicality can significantly change the prediction. In doing so, we demonstrate the existence of overlaps in the predictions of different “frameworks” consisting of conjunctions of theory, conditionalization scheme and typicality assumption. This conclusion highlights the acute challenges involved in using such tests to identify a preferred framework that aims to describe our observational situation in a multiverse.