We study a simple model of thermal dark matter annihilating to standard model neutrinos via the neutrino portal. A (pseudo-)Dirac sterile neutrino serves as a mediator between the visible and the dark sectors, while an approximate lepton number symmetry allows for a large neutrino Yukawa coupling and, in turn, efficient dark matter annihilation. The dark sector consists of two particles, a Dirac fermion and complex scalar, charged under a symmetry that ensures the stability of the dark matter. A generic prediction of the model is a sterile neutrino with a large active-sterile mixing angle that decays primarily invisibly. We derive existing constraints and future projections from direct detection experiments, colliders, rare meson and tau decays, electroweak precision tests, and small scale structure observations. Along with these phenomenological tests, we investigate the consequences of perturbativity and scalar mass fine tuning on the model parameter space. A simple, conservative scheme to confront the various tests with the thermal relic target is outlined, and we demonstrate that much of the cosmologically-motivated parameter space is already constrained. We also identify new probes of this scenario such as multibody kaon decays and Drell-Yan production of $W$ bosons at the LHC.

The mass of the graviton, if nonzero, is usually considered to be very small, e.g., of the Hubble scale, from several observational constraints. In this paper, we propose a gravity model where the graviton mass is very small in the usual weak gravity environments, below all the current graviton mass bounds, but becomes much larger in the strong gravity regime such as a black hole’s vicinity. For black holes in this model, significant deviations from general relativity emerge very close to the black hole horizon and alter the black hole quasinormal modes, which can be extracted from the ringdown wave form of black hole binary mergers. Also, the enhancement of the graviton mass near the horizon can result in echoes in the late-time ringdown, which can be verified in the upcoming gravitational wave observations of higher sensitivity.

We study scale invariance at the quantum level in a perturbative approach. For a scale-invariant classical theory, the scalar potential is computed at a three-loop level while keeping manifest this symmetry. Spontaneous scale symmetry breaking is transmitted at a quantum level to the visible sector (of $\varphi$) by the associated Goldstone mode (dilaton $\sigma$), which enables a scale-invariant regularization and whose vacuum expectation value $⟨\sigma ⟩$ generates the subtraction scale ($\mu$). While the hidden ($\sigma$) and visible sector ($\varphi$) are classically decoupled in $d=4$ due to an enhanced Poincaré symmetry, they interact through (a series of) evanescent couplings $\propto \epsilon$, dictated by the scale invariance of the action in $d=4-2\epsilon$. At the quantum level, these couplings generate new corrections to the potential, as scale-invariant nonpolynomial effective operators ${\varphi }^{2n+4}/{\sigma }^{2n}$. These are comparable in size to “standard” loop corrections and are important for values of $\varphi$ close to $⟨\sigma ⟩$. For $n=1$, 2, the beta functions of their coefficient are computed at three loops. In the IR limit, dilaton fluctuations decouple, the effective operators are suppressed by large $⟨\sigma ⟩$, and the effective potential becomes that of a renormalizable theory with explicit scale symmetry breaking by the DR scheme (of $\mu =\text{constant}$).

Successful leptogenesis within the conventional TeV-scale left-right implementation of type-I seesaw has been shown to require that the mass of the right-handed $W_R^{\pm }$ boson should have a lower bound much above the reach of the Large Hadron Collider. This bound arises from the necessity to suppress the washout of lepton asymmetry due to $W_R^{\pm }$-mediated $\mathrm{\Delta }L\ne 0$ processes. We show that in an alternative quark seesaw realization of left-right symmetry, the above bound can be avoided. Lepton asymmetry in this model is generated not via the usual right-handed neutrino decay but rather via the decay of new heavy scalars producing an asymmetry in the $B-L$ carrying Higgs triplets responsible for type-II seesaw, whose decay leads to the lepton asymmetry.

We apply the covariant derivative expansion of the Coleman-Weinberg potential to the sfermion sector in the minimal supersymmetric standard model, matching it to the relevant dimension-6 operators in the standard model effective field theory at one-loop level. Emphasis is paid to nondegenerate large soft supersymmetry breaking mass squares, and the most general analytical Wilson coefficients are obtained for all pure bosonic dimension-6 operators. In addition to the non-logarithmic contributions, they generally have another logarithmic contributions. Various numerical results are shown, in particular the constraints in the large $X_t$ branch reproducing the 125 GeV Higgs mass can be pushed to high values to almost completely probe the low stop mass region at the future FCC-ee experiment, even given the Higgs mass calculation uncertainty.

We implement inflation in a nonsupersymmetric $SU(5)$ model based on a nonminimal coupling of the axion field to gravity. The isocurvature fluctuations are adequately suppressed, axions comprise the dark matter, proton lifetime estimates are of order $8\times {10}^{34}–3\times {10}^{35}\mathrm{yr}$, and the observed baryon asymmetry arises via nonthermal leptogenesis. The presence of low-scale colored scalars ensures unification of the Standard Model gauge couplings and also helps in stabilizing the electroweak vacuum.

We explore semileptonic $B$ decays to the four lightest excited charm mesons, $D^{**}=\{D_0^{*},D_1^{*},D_1,D_2^{*}\}$, for nonzero charged lepton mass and for all $b\to c\ell \overline{\nu }$ four-Fermi interactions, including calculation of the $\mathcal{O}({\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b})$ and $\mathcal{O}({\alpha }_s)$ corrections to the heavy quark limit for all form factors. In the heavy quark limit, some form factors are suppressed at zero recoil; therefore, the $\mathcal{O}({\mathrm{\Lambda }}_{\mathrm{QCD}}/m_{c,b})$ corrections can be very important. The $D^{**}$ rates exhibit sensitivities to new physics in $b\to c\tau \overline{\nu }$ mediated decays complementary to the $D$ and $D^{*}$ modes. Since they are also important backgrounds to $B\to D^{(*)}\tau \overline{\nu }$, the correct interpretation of future semitauonic $B\to D^{(*)}$ rate measurements requires consistent treatment of both the $D^{**}$ backgrounds and the signals. Our results allow more precise and more reliable calculations of these $B\to D^{**}\ell \overline{\nu }$ decays and are systematically improvable by better data on the $e$ and $\mu$ modes. As an example, we show that the $D^{**}$ rates are more sensitive to a new $\overline{c}{\sigma }_{\mu \nu }b$ tensor interaction than the $D^{(*)}$ rates.

We derive two new sum rules for the unpolarized doubly virtual Compton scattering process on a nucleon, which establish novel low-$Q^2$ relations involving the nucleon’s generalized polarizabilities and moments of the nucleon’s unpolarized structure functions $F_1(x,Q^2)$ and $F_2(x,Q^2)$. These relations facilitate the determination of some structure constants which can only be accessed in off-forward doubly virtual Compton scattering, not experimentally accessible at present. We perform an empirical determination for the proton and compare our results with a next-to-leading-order chiral perturbation theory prediction. We also show how these relations may be useful for a model-independent determination of the low-$Q^2$ subtraction function in the Compton amplitude, which enters the two-photon-exchange contribution to the Lamb shift of (muonic) hydrogen. An explicit calculation of the $\mathrm{\Delta }(1232)$-resonance contribution to the muonic-hydrogen $2P-2S$ Lamb shift yields $-1\pm 1\mu \mathrm{eV}$, confirming the previously conjectured smallness of this effect.

We investigate the restoration of chiral symmetry at finite temperature in the SU(2) quark-meson model, where the mean field approximation is compared to the renormalized version for quarks and mesons. In a combined approach at finite temperature, all the renormalized versions show a crossover transition. The inclusion of different renormalization scales leave the order parameter and the mass spectra nearly untouched but strongly influence the thermodynamics at low temperatures and around the phase transition. We find unphysical results for the renormalized version of mesons and the combined one.

We present a model for Monte Carlo simulation of the fragmentation of a polarized quark. The model is based on string dynamics and the ${{}^{3}P}_0$ mechanism of quark pair creation at string breaking. The fragmentation is treated as a recursive process, where the splitting function of the subprocess $q\to h+q^{\prime }$ depends on the spin density matrix of the quark $q$. The ${{}^{3}P}_0$ mechanism is parametrized by a complex mass parameter $\mu$, the imaginary part of which is responsible for single spin asymmetries. The model has been implemented in a Monte Carlo program to simulate jets made of pseudoscalar mesons. Results for single hadron and hadron pair transverse-spin asymmetries are found to be in agreement with experimental data from SIDIS and $e^{+}{e}^{-}$ annihilation. The model predictions on the jet-handedness are also discussed.

As atmospheric neutrinos propagate through the Earth, vacuumlike oscillations are modified by Standard Model neutral- and charged-current interactions with electrons. Theories beyond the Standard Model introduce heavy, TeV-scale bosons that can produce nonstandard neutrino interactions. These additional interactions may modify the Standard Model matter effect producing a measurable deviation from the prediction for atmospheric neutrino oscillations. The result described in this paper constrains nonstandard interaction parameters, building upon a previous analysis of atmospheric muon-neutrino disappearance with three years of IceCube DeepCore data. The best fit for the muon to tau flavor changing term is ${\epsilon }_{\mu \tau }=-0.0005$, with a 90% C.L. allowed range of $-0.0067<{\epsilon }_{\mu \tau }<0.0081$. This result is more restrictive than recent limits from other experiments for ${\epsilon }_{\mu \tau }$. Furthermore, our result is complementary to a recent constraint on ${\epsilon }_{\mu \tau }$ using another publicly available IceCube high-energy event selection. Together, they constitute the world’s best limits on nonstandard interactions in the $\mu -\tau$ sector.

We investigate the asymptotic safety conjecture for quantum gravity including curvature invariants beyond Ricci scalars. Our strategy is put to work for families of gravitational actions which depend on functions of the Ricci scalar, the Ricci tensor, and products thereof. Combining functional renormalization with high order polynomial approximations and full numerical integration we derive the renormalization group flow for all couplings and analyse their fixed points, scaling exponents, and the fixed point effective action as a function of the background Ricci curvature. The theory is characterized by three relevant couplings. Higher-dimensional couplings show near-Gaussian scaling with increasing canonical mass dimension. We find that Ricci tensor invariants stabilize the UV fixed point and lead to a rapid convergence of polynomial approximations. We apply our results to models for cosmology and establish that the gravitational fixed point admits inflationary solutions. We also compare findings with those from $f(R)$-type theories in the same approximation and pin-point the key new effects due to Ricci tensor interactions. Implications for the asymptotic safety conjecture of gravity are indicated.

Using the heat kernel method, we compute nonrelativistic trace anomalies for Schrödinger theories in flat spacetime, with a generic background gauge field for the particle number symmetry, both for a free scalar and a free fermion. The result is genuinely nonrelativistic, and it has no counterpart in the relativistic case. Contrary to naive expectations, the anomaly is not gauge invariant; this is similar to the nongauge covariance of the non-Abelian relativistic anomaly. We also show that, in the same background, the gravitational anomaly for a nonrelativistic scalar vanishes.

This is the first of a series of papers in which we use analyticity properties of quantum fields propagating on a spacetime to uncover a new multiverse geometry when the classical geometry has horizons and/or singularities. The nature and origin of the “multiverse” idea presented in this paper, that is shared by the fields in the standard model coupled to gravity, are different from other notions of a multiverse. Via analyticity we are able to establish definite relations among the universes. In this paper we illustrate these properties for the extended Rindler space, while black hole spacetime and the cosmological geometry of mini-superspace (see Appendix B) will appear in later papers. In classical general relativity, extended Rindler space is equivalent to flat Minkowski space; it consists of the union of the four wedges in $(u,v)$ light-cone coordinates as in Fig. 1. In quantum mechanics, the wavefunction is an analytic function of $(u,v)$ that is sensitive to branch points at the horizons $u=0$ or $v=0$, with branch cuts attached to them. The wave function is uniquely defined by analyticity on an infinite number of sheets in the cut analytic $(u,v)$ spacetime. This structure is naturally interpreted as an infinite stack of identical Minkowski geometries, or “universes”, connected to each other by analyticity across branch cuts, such that each sheet represents a different Minkowski universe when $(u,v)$ are analytically continued to the real axis on any sheet. We show in this paper that, in the absence of interactions, information does not flow from one Rindler sheet to another. By contrast, for an eternal black hole spacetime, which may be viewed as a modification of Rindler that includes gravitational interactions, analyticity shows how information is “lost” due to a flow to other universes, enabled by an additional branch point and cut due to the black hole singularity.

We present a detailed derivation of the power corrections to the factorization theorem for the 0-jettiness event shape variable $\mathcal{T}$. Our calculation is performed directly in QCD without using the formalism of effective field theory. We analytically calculate the next-to-leading logarithmic power corrections for small $\mathcal{T}$ at next-to-leading order in the strong coupling constant, extending previous computations which obtained only the leading-logarithmic power corrections. We address a discrepancy in the literature between results for the leading-logarithmic power corrections to a particular definition of 0-jettiness. We present a numerical study of the power corrections in the context of their application to the $N$-jettiness subtraction method for higher-order calculations, using gluon-fusion Higgs production as an example. The inclusion of the next-to-leading-logarithmic power corrections further improves the numerical efficiency of the approach beyond the improvement obtained from the leading-logarithmic power corrections.

The quark-meson model is often used as a low-energy effective model for QCD to study the chiral transition at finite temperature $T$, baryon chemical potential ${\mu }_B$, and isospin chemical potential ${\mu }_I$. We determine the parameters of the model by matching the meson and quark masses, as well as the pion decay constant to their physical values using the on shell (OS) and modified minimal subtraction ($\overline{\mathrm{MS}}$) schemes. In this paper, the existence of different phases at zero temperature is studied. In particular, we investigate the competition between an inhomogeneous chiral condensate and a homogeneous pion condensate. For the inhomogeneity, we use a chiral-density wave ansatz. For a sigma mass of 600 MeV, we find that an inhomogeneous chiral condensate exists only for pion masses below approximately 37 MeV. We also show that due to our parameter fixing, the onset of pion condensation takes place exactly at ${\mu }_I^c=\frac{1}{2}{m}_{\pi }$ in accordance with exact results.

We have simulated the SU(4) lattice gauge theory coupled to dynamical fermions in the fundamental and two-index antisymmetric (sextet) representations simultaneously. Such theories arise naturally in the context of composite Higgs models that include a partially composite top quark. We describe the low-lying meson spectrum of the theory and fit the pseudoscalar masses and decay constants to chiral perturbation theory. We infer as well the mass and decay constant of the Goldstone boson corresponding to the nonanomalous U(1) symmetry of the model. Our results are broadly consistent with large-$N_c$ scaling and vector-meson dominance.

We use light-front holography to estimate the valence quark and the meson cloud contributions to the nucleon axial form factor. The free couplings of the holographic model are determined by the empirical data and by the information extracted from lattice QCD. The holographic model provides a good description of the empirical data when we consider a meson cloud mixture of about 30% in the physical nucleon state. The estimate of the valence quark contribution to the nucleon axial form factor compares well with the lattice QCD data for small pion masses. Our estimate of the meson cloud contribution to the nucleon axial form factor has a slower falloff with the square momentum transfer compared to typical estimates from quark models with meson cloud dressing.

A search is presented for heavy vectorlike quarks (VLQs) that couple only to light quarks in proton-proton collisions at $\sqrt{s}=8\mathrm{TeV}$ at the LHC. The data were collected by the CMS experiment during 2012 and correspond to an integrated luminosity of $19.7{\mathrm{fb}}^{-1}$. Both single and pair production of VLQs are considered. The single-production search is performed for down-type VLQs (electric charge of magnitude $1/3$), while the pair-production search is sensitive to up-type (charge of magnitude $2/3$) and down-type VLQs. Final states with at least one muon or one electron are considered. No significant excess over standard model expectations is observed, and lower limits on the mass of VLQs are derived. The lower limits range from 400 to 1800 GeV, depending on the single-production cross section and the VLQ branching fractions $\mathcal{B}$ to $W$, $Z$, and Higgs bosons. When considering pair production alone, VLQs with masses below 845 GeV are excluded for $\mathcal{B}(W)=1.0$, and below 685 GeV for $\mathcal{B}(W)=0.5$, $\mathcal{B}(Z)=\mathcal{B}(H)=0.25$. The results are more stringent than those previously obtained for single and pair production of VLQs coupled to light quarks.

We study interacting fixed points and phase diagrams of simple and semisimple quantum field theories in four dimensions involving non-Abelian gauge fields, fermions and scalars in the Veneziano limit. Particular emphasis is put on new phenomena which arise due to the semisimple nature of the theory. Using matter field multiplicities as free parameters, we find a large variety of interacting conformal fixed points with stable vacua and crossovers inbetween. Highlights include semisimple gauge theories with exact asymptotic safety, theories with one or several interacting fixed points in the IR, theories where one of the gauge sectors is both UV free and IR free, and theories with weakly interacting fixed points in the UV and the IR limits. The phase diagrams for various simple and semisimple settings are also given. Further aspects such as perturbativity beyond the Veneziano limit, conformal windows, and implications for model building are discussed.