We explore whether perturbative interacting fixed points in matter systems can persist under the impact of quantum gravity. We first focus on semisimple gauge theories and show that the leading order gravity contribution evaluated within the functional Renormalization Group framework preserves the perturbative fixed-point structure in these models discovered in [J. K. Esbensen, T. A. Ryttov, and F. Sannino, Phys. Rev. D 93, 045009 (2016).]. We highlight that the quantum-gravity contribution alters the scaling dimension of the gauge coupling, such that the system exhibits an effective dimensional reduction. We secondly explore the effect of metric fluctuations on asymptotically safe gauge-Yukawa systems which feature an asymptotically safe fixed point [D. F. Litim and F. Sannino, J. High Energy Phys. 12 (2014) 178.]. The same effective dimensional reduction that takes effect in pure gauge theories also impacts gauge-Yukawa systems. There, it appears to lead to a split of the degenerate free fixed point into an interacting infrared attractive fixed point and a partially ultraviolet attractive free fixed point. The quantum-gravity induced infrared fixed point moves towards the asymptotically safe fixed point of the matter system, and annihilates it at a critical value of the gravity coupling. Even after that fixed-point annihilation, graviton effects leave behind new partially interacting fixed points for the matter sector.

We assess the utility of an optimization-based data assimilation (D.A.) technique for treating the problem of nonlinear neutrino flavor transformation in core-collapse supernovae. D.A. uses measurements obtained from a physical system to estimate the state variable evolution and parameter values of the associated model. Formulated as an optimization procedure, D.A. can offer an integration-blind approach to predicting model evolution, which offers an advantage for models that thwart solution via traditional numerical integration techniques. Further, D.A. performs most optimally for models whose equations of motion are nonlinearly coupled. In this exploratory work, we consider a simple steady-state model with two monoenergetic neutrino beams coherently interacting with each other and a background medium. As this model can be solved via numerical integration, we have an independent consistency check for D.A. solutions. We find that the procedure can capture key features of flavor evolution over the entire trajectory, even given measurements of neutrino flavor only at the endpoint, and with an assumed known initial flavor distribution. Further, the procedure permits an examination of the sensitivity of flavor evolution to estimates of unknown model parameters, locates degeneracies in parameter space, and can identify the specific measurements required to break those degeneracies.

We study the pair-production process in the presence of two counterpropagating linearly polarized short laser pulses. By means of a nonperturbative technique, we take into account the full coordinate dependence of the external field going beyond the dipole and standing-wave approximations. In particular, we analyze the momentum distribution of particles created. It is demonstrated that the spatial variations of the laser pulses may play a crucial role. The more accurate treatment reveals a number of prominent features: the pair-production probabilities become considerably smaller, the quantitative behavior of the momentum spectra changes dramatically, and the pulse shape effects become much less pronounced. The results of our study are expected to be very important for future theoretical and experimental investigations.

The LHCb Collaboration has recently reported a $2.5\sigma$ discrepancy with respect to the predicted value in a test of lepton universality in the ratio $R_{K^{*}}=\mathrm{BR}(B\to K^{*}{\mu }^{+}{\mu }^{-})/\mathrm{BR}(B\to K^{*}{e}^{+}{e}^{-})$. Coupled with an earlier observation of a similar anomaly in $R_K$, this has generated significant excitement. A number of new physics scenarios have been proposed to explain the anomaly. In this work we consider simplified limits on $Z^{\prime }$ models from ATLAS and CMS searches for new resonances in dilepton and dijet modes, and we use the simplified limits variable $\zeta$ to correlate the results of the resonance and B-decay experiments. By examining minimal $Z^{\prime }$ models that can accommodate the observed LHCb results, we show that the high-mass resonance search results are beginning to be sensitive to these models and that future results will be more informative.

For a field theory with a gravitational dual, we study holographic fidelity susceptibility for two states related by a deformation of a relevant operator. To do so, we study the backreaction of a massive scalar field on the asymptotic behavior of the metric in an Einstein gravity coupled to a massive scalar field. Identifying the two states, holographically, with the original and backreacted geometries, the corresponding holographic fidelity susceptibility is given by the difference of the volume of an extremal time slice evaluated on the original and backreacted geometries.

In this paper we study a numerical implementation for the initial boundary value formulation for the generalized conformal field equations. We propose a formulation which is well suited for the study of the long-time behavior of perturbed exact solutions such as a Schwarzschild or even a Kerr black hole. We describe the derivation of the implemented equations which we give in terms of the space-spinor formalism. We discuss the conformal Gauss gauge, and a slight generalization thereof which seems to be particularly useful in the presence of boundaries. We discuss the structure of the equations at the boundary and propose a method for imposing boundary conditions which allow the correct number of degrees of freedom to be freely specified while still preserving the constraints. We show that this implementation yields a numerically well-posed system by testing it on a simple case of gravitational perturbations of Minkowski space-time and subsequently with gravitational perturbations of Schwarzschild space-time.

Gravitational waves can be used to test general relativity (GR) in the highly dynamical strong-field regime. Scalar-tensor theories of gravity are natural alternatives to GR that can manifest nonperturbative phenomena in neutron stars (NSs). One such phenomenon, known as dynamical scalarization, occurs in coalescing binary NS systems. Ground-based gravitational-wave detectors may be sensitive to this effect, and thus could potentially further constrain scalar-tensor theories. This type of analysis requires waveform models of dynamically scalarizing systems; in this work we devise an analytic model of dynamical scalarization using an effective action approach. For the first time, we compute the Newtonian-order Hamiltonian describing the dynamics of a dynamically scalarizing binary in a self-consistent manner. Despite only working to leading order, the model accurately predicts the frequency at which dynamical scalarization occurs. In conjunction with Landau theory, our model allows one to definitively establish dynamical scalarization as a second-order phase transition. We also connect dynamical scalarization to the related phenomena of spontaneous scalarization and induced scalarization; these phenomena are naturally encompassed into our effective action approach.

Spherically symmetric relativistic stars with a polytropic equation of state (EoS), which possess local pressure anisotropy, are considered within the framework of general relativity. The generalized Lane-Emden equations are derived for the arbitrary anisotropy parameter $\mathrm{\Delta }=p_t-p_r$ ($p_t$ and $p_r$ being the transverse and radial pressure, respectively). They are then applied to some special ansatz for the anisotropy parameter in the form of a differential relation between the anisotropy parameter $\mathrm{\Delta }$ and the metric function $\nu$. The analytical solutions of the obtained equations are found for incompressible fluid stars and then used for getting their mass-radius relation, gravitational energy, and binding energy. Also, following the Chandrasekhar variational approach, the dynamical stability of incompressible anisotropic fluid stars with a polytropic EoS against radial oscillations is studied. It is shown that the local pressure anisotropy with $p_t>p_r$ can make the incompressible fluid stars unstable with respect to radial oscillations, in contrast to incompressible isotropic fluid stars with a polytropic EoS which are dynamically stable.

We study BPS bound states of little strings in a limit where they realize monopole strings in five dimensional gauge theories. The latter have gauge group $U(M{)}^N$ and arise from compactification of (1,0) little string theories of type $A_{M-1}\times A_{N-1}$. We find evidence that the partition function of a certain subclass of monopole strings of charge $(k,\dots ,k)$ ($k\ge 1$) is expressible as the partition function of a symmetric orbifold sigma model, whose target space is precisely the symmetric product of the moduli space of monopoles with charge $(1,\dots ,1)$.

We advocate the use of on-shell constrained $M_2$ variables in order to mitigate the combinatorial problem in supersymmetry-like events with two invisible particles at the LHC. We show that in comparison to other approaches in the literature, the constrained $M_2$ variables provide superior ansätze for the unmeasured invisible momenta and therefore can be usefully applied to discriminate combinatorial ambiguities. We illustrate our procedure with the example of dilepton $t\overline{t}$ events. We critically review the existing methods based on the Cambridge $M_{T2}$ variable and MAOS reconstruction of invisible momenta, and show that their algorithm can be simplified without loss of sensitivity, due to a perfect correlation between events with complex solutions for the invisible momenta and events exhibiting a kinematic endpoint violation. Then we demonstrate that the efficiency for selecting the correct partition is further improved by utilizing the $M_2$ variables instead. Finally, we also consider the general case when the underlying mass spectrum is unknown, and no kinematic endpoint information is available.

The width of the $f_1(1285)\to e^{+}{e}^{-}$ decay is calculated in the vector meson dominance model. The result depends on the relative phase between two coupling constants describing $f_1\to {\rho }^0\gamma$ decay. The width $\mathrm{\Gamma }(f_1\to e^{+}{e}^{-})$ is estimated to be $\simeq 0.07–0.19\mathrm{eV}$. Direct $f_1$ production in $e^{+}{e}^{-}$ collisions is discussed, and the $e^{+}{e}^{-}\to f_1\to a_0\pi \to \eta \pi \pi$ cross section is calculated. Charge asymmetry in the $e^{+}{e}^{-}\to \eta {\pi }^{+}{\pi }^{-}$ reaction due to interference between $e^{+}{e}^{-}\to f_1$ and $e^{+}{e}^{-}\to \eta {\rho }^0$ amplitudes is studied.

Recently there has been interest in the correlation between $R(D^{*})$ and the branching ratio (BR) of $B_c^{-}\to \tau \overline{\nu }$ in models with a charged scalar $H^{\pm }$. Any enhancement of $R(D^{*})$ by $H^{\pm }$ alone (in order to agree with current data) also enhances $\mathrm{BR}(B_c^{-}\to \tau \overline{\nu })$, for which there has been no direct search at hadron colliders. We show that LEP data taken at the $Z$ peak requires $\mathrm{BR}(B_c^{-}\to \tau \overline{\nu })\lesssim 10\%$, and this constraint is significantly stronger than the recent constraint $\mathrm{BR}(B_c^{-}\to \tau \overline{\nu })\lesssim 30\%$ from considering the lifetime of $B_c$. In order to respect this new constraint, any explanation of the $R(D)$ and $R(D^{*})$ anomaly in terms of $H^{\pm }$ alone would require the future measurements of $R(D^{*})$ to be even closer to the Standard Model prediction. A stronger limit on $\mathrm{BR}(B_c^{-}\to \tau \overline{\nu })$ (or its first measurement) would be obtained if the L3 Collaboration used all its data taken at the $Z$ peak.

The scaling dimension of the first excited state in two-dimensional conformal field theories (CFTs) satisfies a universal upper bound. Using the modular bootstrap, we extend this result to CFTs with ${\mathcal{W}}_3$ algebras which are generically dual to higher spin theories in ${\mathrm{AdS}}_3$. Assuming unitarity and modular invariance, we show that the conformal weights $h$, $\overline{h}$ of the lightest charged state satisfy $h<c/12+\mathcal{O}(1)$ and $\overline{h}<\overline{c}/12+\mathcal{O}(1)$ in the limit where the central charges $c$, $\overline{c}$ are large. Furthermore, we show that in this limit any consistent CFT with ${\mathcal{W}}_3$ currents must contain at least one state whose ${\mathcal{W}}_3$ charge $w$ obeys $|w|>4|h-c/24|/\sqrt{10\pi c}+\mathcal{O}(1)$. We discuss hints on the existence of stronger bounds and comment on the interpretation of our results in the dual higher spin theory.

Pure massive gravity is strongly coupled at a certain low scale, known as ${\mathrm{\Lambda }}_3$. I show that the theory can be embedded into another one, with new light degrees of freedom, to increase the strong scale to a significantly larger value. Certain universal aspects of the proposed mechanism are discussed, notably that the coupling of the longitudinal mode to a stress tensor is suppressed, thus making the linear theory consistent with the fifth-force exclusion. An example of the embedding theory studied in detail is five-dimensional anti-de Sitter massive gravity, with a large cosmological constant. In this example, the four-dimensional (4D) strong scale can be increased by 19 orders of magnitude. Holographic duality then suggests that the strong scale of the 4D massive gravity can be increased by coupling it to a 4D nonlocal conformal field theory, endowed with a UV cutoff; however, the five-dimensional classical gravity picture appears to be more tractable.

In this paper, we study optical properties in terms of weak and strong (retrolensing) gravitational lensing around a black hole on the brane. The black hole is described by the Reissener-Nordström metric, where the electric charge is replaced by the Weyl tidal charge which acts in consonance with mass. It is, therefore, expected that gravitational lensing effects would be enhanced by the tidal charge, and that is what we verify. We also study the shadow of a braneworld black hole in plasma and show that the tidal charge increases the size of the black hole shadow. We finally consider energy emission from the hole by thermal radiation which is also increased due to tidal charge.

A change in the fundamental constants of nature or plasma effects in the early universe could stabilize ${}^8\mathrm{Be}$ against decay into two ${}^4\mathrm{He}$ nuclei. Coc et al. examined the former effect on big bang nucleosynthesis as a function of $B_8$, the mass difference between two ${}^4\mathrm{He}$ nuclei and a single ${}^8\mathrm{Be}$ nucleus, and found no effects for $B_8\le 100\mathrm{keV}$. Here we examine stable ${}^8\mathrm{Be}$ with larger $B_8$ and also allow for a variation in the rate for ${}^4\text{He}+{}^4\text{He}\to {}^8\mathrm{Be}$ to determine the threshold for interesting effects. We find no change to standard big bang nucleosynthesis for $B_8<1\mathrm{MeV}$. For $B_8\gtrsim 1\mathrm{MeV}$ and a sufficiently large reaction rate, a significant fraction of ${}^4\mathrm{He}$ is burned into ${}^8\mathrm{Be}$, which fissions back into ${}^4\mathrm{He}$ when $B_8$ assumes its present-day value, leaving the primordial ${}^4\mathrm{He}$ abundance unchanged. However, this sequestration of ${}^4\mathrm{He}$ results in a decrease in the primordial ${}^7\mathrm{Li}$ abundance. Primordial abundances of ${}^7\mathrm{Li}$ consistent with observationally inferred values can be obtained for reaction rates similar to those calculated for the present-day (unbound ${}^8\mathrm{Be}$) case. Even for the largest binding energies and largest reaction rates examined here, only a small fraction of ${}^8\mathrm{Be}$ is burned into heavier elements, consistent with earlier studies. There is no change in the predicted deuterium abundance for any model we examined.

A Higgs-like dilaton owns couplings that differ from those of the Standard Model Higgs and of a generic composite Higgs. The complete bosonic basis for a Higgs-like dilaton is presented at the first subleading order. A comparison with the Standard Model, Standard Model Effective Field Theory, and the generic Lagrangian for the minimal $SO(5)/SO(4)$ composite Higgs model is performed. Observables that can disentangle the different hypotheses are identified.

We analyze possible effects of the dark matter environment on the atomic clock stability measurements. The dark matter is assumed to exist in the form of waves of ultralight scalar fields or in the form of topological defects (monopoles and strings). We identify dark matter signal signatures in clock Allan deviation plots that can be used to constrain the dark matter coupling to the Standard Model fields. The existing data on the ${\mathrm{Al}}^{+}/{\mathrm{Hg}}^{+}$ clock comparison are used to put new limits on the dilaton dark matter in the region of masses $m_{\varphi }>{10}^{-15}\mathrm{eV}$. We also estimate the sensitivities of future atomic clock experiments in space, including the cesium microwave and strontium optical clocks aboard the International Space Station, as well as a potential nuclear clock. These experiments are expected to put new limits on the topological dark matter in the range of masses ${10}^{-10}\mathrm{eV}<m_{\varphi }<{10}^{-6}\mathrm{eV}$.