A remarkable prediction of the Standard Model is that, in the absence of corrections lifting the energy density, the Higgs potential becomes negative at large field values. If the Higgs field samples this part of the potential during inflation, the negative energy density may locally destabilize the spacetime. We use numerical simulations of the Einstein equations to study the evolution of inflation-induced Higgs fluctuations as they grow towards the true (negative-energy) minimum. These simulations show that forming a single patch of true vacuum in our past light cone during inflation is incompatible with the existence of our Universe; the boundary of the true vacuum region grows outward in a causally disconnected manner from the crunching interior, which forms a black hole. We also find that these black hole horizons may be arbitrarily elongated—even forming black strings—in violation of the hoop conjecture. By extending the numerical solution of the Fokker-Planck equation to the exponentially suppressed tails of the field distribution at large field values, we derive a rigorous correlation between a future measurement of the tensor-to-scalar ratio and the scale at which the Higgs potential must receive stabilizing corrections in order for the Universe to have survived inflation until today.

We demonstrate the importance of correctly implementing RG running and choosing the RG scale when calculating quantum corrections to inflaton dynamics. We show that such corrections are negligible for single-field inflation, in the sense of not altering the viable region in the $n_s-r$ plane, when imposing Planck constraints on $A_s$. Surprisingly, this also applies, in a nontrivial way, for an inflaton coupled to additional spectator degrees of freedom. The result relies on choosing the renormalization scale (pseudo-)optimally, thereby avoiding unphysical large logarithmic corrections to the Friedmann equations and large running of the couplings. We find that the viable range of parameters of the potential is altered relative to the classical limit, and we find an upper limit of $g\simeq {10}^{-4}$ on the value of the inflaton-spectator portal coupling still allowing for inflation and an upper limit of $g\simeq {10}^{-5}$ for inflation to correctly reproduce the scalar amplitude of fluctuations $A_s$.

Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multiphonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.

We present an updated calculation of the uncertainties on the atmospheric muon-neutrino flux arising from cosmic-ray primaries. For the first time, we include recent measurements of the cosmic-ray primaries collected since 2005. We apply a statistical technique that allows the determination of correlations between the parameters of the Gaisser, Stanev, Honda, and Lipari primary-flux parametrization and the incorporation of these correlations into the uncertainty on the muon-neutrino flux. We obtain an uncertainty related to the primary cosmic rays of around (5–15)%, depending on energy, which is about a factor of 2 smaller than the previously determined uncertainty. The hadron production uncertainty is added in quadrature to obtain the total uncertainty on the neutrino flux, which is reduced by $\approx 5\%$. To take into account an unexpected hardening of the spectrum of primaries above energies of 100 GeV observed in recent measurements, we propose an alternative parametrization and discuss its impact on the neutrino flux uncertainties.

Based on the assumption of two-quark structure for the light scalar mesons, within the perturbative QCD approach, we investigate the $B\to D^{(*)}S(q=u,d,s)$ decays induced by the $b\to u$ transition, with $S$ denoting a light scalar meson. Under two different scenarios, the branching ratios of 96 decay modes have been calculated, most of which are in the range ${10}^{-5}$ to ${10}^{-8}$. These results can be tested in the ongoing LHCb experiment and the forthcoming Belle-II experiment. The comparison between our predictions and the experimental data allows us to probe the inner structure of the scalar mesons. In the standard model, since all decays can only occur through tree operators, there are no $CP$ asymmetries. We note that, due to the mass difference between charm quark and light quarks, the contribution from annihilation diagrams will be enhanced sizably, especially for these color-suppressed or pure-annihilation-type decay modes. We also find that the branching ratios of color-favored decays are sensitive to the different scenarios, so their measurement will help us differentiate the different scenarios. It is also found that the ratios between $\mathrm{Br}(B\to D^{(*)}\sigma )$ and $\mathrm{Br}(B\to D^{(*)}{f}_0(980))$ can be used to determine the mixing angle of $\sigma$ and $f_0(980)$.

The two-photon transition of $\overline{c}c$ quarkonia are studied within a covariant approach based on the consistent truncation scheme of the quantum chromodynamics Dyson-Schwinger equation for the quark propagator and the Bethe-Salpeter equation for the mesons. We find the decay widths of ${\eta }_c\to \gamma \gamma$ and ${\chi }_{c0,2}\to \gamma \gamma$ in good agreement with experimental data. The obtained transition form factor of ${\eta }_c\to \gamma {\gamma }^{*}$ for a wide range of spacelike photon-momentum-transfer squared is also in agreement with the experimental findings of the BABAR experiment. As a by-product, the decay widths of ${\eta }_b,{\chi }_{b0,2}\to \gamma \gamma$ and the transition form factor of ${\eta }_b,{\chi }_{c0,b0}\to \gamma {\gamma }^{*}$ are predicted, which await experimental testing.

The $B\to a_1{\ell }^{+}{\ell }^{-}$ decays occur by the electroweak penguin and box diagrams, which can be performed through the flavor changing neutral current (FCNC). We calculate the form factors of the FCNC $B\to a_1$ transitions in the light-cone sum rules approach, up to twist-4 distribution amplitudes of the axial vector meson $a_1$. Forward-backward asymmetry, as well as branching ratios of $B\to a_1{\ell }^{+}{\ell }^{-}$, and $B\to a_1\gamma$ decays are considered. A comparison is also made between our results and the predictions of other methods.

We discuss the systematic evaluation of three-loop vacuum integrals with arbitrary masses. Using integration by parts, the general integral of this type can be reduced algebraically to a few basis integrals. We define a set of modified finite basis integrals that are particularly convenient for expressing renormalized quantities. The basis integrals can be computed numerically by solving coupled first-order differential equations, using as boundary conditions the analytically known special cases that depend on only one mass scale. We provide the results necessary to carry this out and introduce an implementation in the form of a public software package called 3vil (three-loop Vacuum Integral Library), which efficiently computes the numerical values of the basis integrals for any specified masses. Note that 3vil is written in c, and can be linked from c, c++, or fortran code.

We estimate contributions from Kaluza-Klein excitations of third generation quarks and gauge bosons to the branching ratio of $B\to X_s\gamma$ decay process in the five-dimensional universal extra dimensional scenario with nonvanishing boundary localized terms. This model is conventionally known as the nonminimal universal extra dimensional model. We have derived the lower limit on the size of the extra dimension by comparing our theoretical estimation of the branching ratio that includes next-to-next-to leading order QCD corrections with its experimentally measured value. Coefficients of the boundary localized terms have also been constrained. 95% C.L. lower limit on the inverse of the radius of compactification ($R^{-1}$) can be as large as 670 GeV for some choice of the value of coefficients of boundary localized terms.

Our understanding of the Universe is known to be incomplete, and new gauge forces beyond those of the Standard Model might be crucial to describing its observed properties. A minimal and well-motivated possibility is a pure Yang-Mills non-Abelian dark gauge force with no direct connection to the Standard Model. We determine here the relic abundances of the glueball bound states that arise in such theories and investigate their cosmological effects. Glueballs are first formed in a confining phase transition, and their relic densities are set by a network of annihilation and transfer reactions. The lightest glueball has no lighter states to annihilate into, and its yield is set mainly by $3\to 2$ number-changing processes which persistently release energy into the glueball gas during freeze-out. The abundances of the heavier glueballs are dominated by $2\to 2$ transfer reactions and tend to be much smaller than the lightest state. We also investigate potential connectors between the dark force and the Standard Model that allow some or all of the dark glueballs to decay. If the connection is weak, the lightest glueball can be very long-lived or stable and is a viable dark matter candidate. For stronger connections, the lightest glueball will decay quickly, but other heavier glueball states can remain stable and contribute to the dark matter density.

We study a mechanism where the dark matter number density today arises from asymmetries generated in the dark sector in the early Universe, even though the total dark matter number remains zero throughout the history of the Universe. The dark matter population today can be completely symmetric, with annihilation rates above those expected from thermal weakly interacting massive particles. We give a simple example of this mechanism using a benchmark model of flavored dark matter. We discuss the experimental signatures of this setup, which arise mainly from the sector that annihilates the symmetric component of dark matter.

We present a lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^{*}(1440)$ resides in experiment. The study is based on the PACS-CS ensemble of gauge configurations with $N_f=2+1$ Wilson-clover dynamical fermions, $m_{\pi }\simeq 156\mathrm{MeV}$ and $L\simeq 2.9\mathrm{fm}$. In addition to a number of $qqq$ interpolating fields, we implement operators for $N\pi$ in $p$-wave and $N\sigma$ in $s$-wave. In the center-of-momentum frame we find three eigenstates below 1.65 GeV. They are dominated by $N(0)$, $N(0)\pi (0)\pi (0)$ [mixed with $N(0)\sigma (0)$] and $N(p)\pi (-p)$ with $p\simeq 2\pi /L$, where momenta are given in parentheses. This is the first simulation where the expected multi-hadron states are found in this channel. The experimental $N\pi$ phase shift would—in the approximation of purely elastic $N\pi$ scattering—imply an additional eigenstate near the Roper mass $m_R\simeq 1.43\mathrm{GeV}$ for our lattice size. We do not observe any such additional eigenstate, which indicates that $N\pi$ elastic scattering alone does not render a low-lying Roper. Coupling with other channels, most notably with $N\pi \pi$, seems to be important for generating the Roper resonance, reinforcing the notion that this state could be a dynamically generated resonance. Our results are in line with most of the previous lattice studies based just on $qqq$ interpolators, which did not find a Roper eigenstate below 1.65 GeV. The study of the coupled-channel scattering including a three-particle decay $N\pi \pi$ remains a challenge.

We show that universality near a critical end point implies a characteristic relation between third- and fourth-order baryon susceptibilities ${\chi }_3$ and ${\chi }_4$, resulting in a banana-shaped loop when ${\chi }_4$ is plotted as a function of ${\chi }_3$ along a freeze-out line. This result relies only on the derivative relation between ${\chi }_3$ and ${\chi }_4$, the enhancement of the correlation length and the scaling symmetry near a critical point, and the freeze-out line near the critical point not too parallel to the ${\mu }_B$ axis. Including the individual enhancements of ${\chi }_3$ and ${\chi }_4$ near a critical point, these features may be a consistent set of observations supporting the interpretation of baryon fluctuation data as arising from criticality.

We show how an excess in the diphoton channel can be the effect of neither a resonance nor an end point in a cascade decay, but rather of a threshold for virtual production of a pair of extra quarks, each with half of peak invariant mass, onsetting in both the $gg$-initiated production and the $\gamma \gamma$-induced decay of an off-shell $Z$ boson. For our analysis we consider as a paradigmatic example the 750 GeV excess previously seen at the end of 2015 with the run 2 data of the LHC but not confirmed with 2016 data.

Within the superfield approach, we consider the nonlocal generalization of the Wess-Zumino model and calculate the one-loop low-energy contributions to the effective action. Four different nonlocal models are considered, among which only the first model does not reduce to the standard Wess-Zumino model when we take the parameter of nonlocality of the model, $\mathrm{\Lambda }$, much greater than any energy scale; in addition, this model also depends on an extra parameter $\xi$. As to the other three models, the result looks like the renormalized effective potential for the usual Wess-Zumino model, where the normalization scale $\mu$ is replaced by the $\mathrm{\Lambda }$. Moreover, the fourth model displays a divergence which can be eliminated through the appropriate wave function renormalization.

We investigate a link between the energy-momentum dispersion relation and the spectral distance in the context of a Lorentzian almost-commutative spectral geometry, defined by the product of Minkowski spacetime and an internal discrete noncommutative space. Using the causal structure, the almost-commutative manifold can be identified with a pair of four-dimensional Minkowski spacetimes embedded in a five-dimensional Minkowski geometry. Considering fermions traveling within the light cone of the ambient five-dimensional spacetime, we then derive the energy-momentum dispersion relation.

Local and global scaling solutions for $O(N)$ symmetric scalar field theories are studied in the complexified field plane with the help of the renormalization group. Using expansions of the effective action about small, large, and purely imaginary fields, we obtain and solve exact recursion relations for all couplings and determine the $3d$ Wilson-Fisher fixed point analytically. For all $O(N)$ universality classes, we further establish that Wilson-Fisher fixed point solutions display singularities in the complex field plane, which dictate the radius of convergence for real-field expansions of the effective action. At infinite $N$, we find closed expressions for the convergence-limiting singularities and prove that local expansions of the effective action are powerful enough to uniquely determine the global Wilson-Fisher fixed point for any value of the fields. Implications of our findings for interacting fixed points in more complicated theories are indicated.

We perform the covariant canonical quantization of the $CPT$- and Lorentz-symmetry-violating photon sector of the minimal Standard-Model Extension, which contains a general (timelike, lightlike, or spacelike) fixed background tensor $k_{AF}^{\mu }$. Well-known stability issues, arising from complex-valued energy states, are solved by introducing a small photon mass, orders of magnitude below current experimental bounds. We explicitly construct a covariant basis of polarization vectors, in which the photon field can be expanded. We proceed to derive the Feynman propagator and show that the theory is microcausal. Despite the occurrence of negative energies and vacuum-Cherenkov radiation, we do not find any runaway stability issues, because the energy remains bounded from below. An important observation is that the ordering of the roots of the dispersion relations is the same in any observer frame, which allows for a frame-independent condition that selects the correct branch of the dispersion relation. This turns out to be critical for the consistency of the quantization. To our knowledge, this is the first system for which quantization has consistently been performed, in spite of the fact that the theory contains negative energies in some observer frames.

We investigate the properties of spherically symmetric black-hole solutions in the generalized Einstein-Skyrme model theory in four-dimensional asymptotically anti–de Sitter spacetime. The dependences of the Skyrmion fields on the cosmological constant and on the strength of the effective gravitational coupling are examined. We show that the increase of the absolute value of the cosmological constant qualitatively yields the same effect as increasing the effective gravitational coupling. We confirm that, similar to the model in asymptotically flat spacetime, a necessary condition for the existence of black holes with Skyrmionic hair is the inclusion of the Skyrme term.

We study the thermal transport properties of general conformal field theories (CFTs) on curved spacetimes in the leading order viscous hydrodynamic limit. At the level of linear response, we show that the thermal transport is governed by a system of forced linearized Navier-Stokes equations on a curved space. Our setup includes CFTs in flat spacetime that have been deformed by spatially dependent and periodic local temperature variations or strains that have been applied to the CFT, and hence is relevant to CFTs arising in condensed matter systems at zero charge density. We provide specific examples of deformations which lead to thermal backflow driven by a dc source: that is, the thermal currents locally flow in the opposite direction to the applied dc thermal source. We also consider thermal transport for relativistic quantum field theories that are not conformally invariant.