We study the implications of the recent results on neutrinoless double beta decay ($0\nu \beta \beta$) from GERDA-I (${}^{76}\mathrm{Ge}$) and $\mathrm{KamLAND}\mathrm{\text{−}}\mathrm{Zen}+\mathrm{EXO}\mathrm{\text{−}}200$ (${}^{136}\mathrm{Xe}$) and the upper limit on the sum of light neutrino masses from Planck. We show that the upper limits on the effective neutrino mass from ${}^{136}\mathrm{Xe}$ are stronger than those from ${}^{76}\mathrm{Ge}$ for most of the recent calculations of the nuclear matrix elements (NMEs). We also analyze the compatibility of these limits with the claimed observation in ${}^{76}\mathrm{Ge}$ and show that while the updated claim value is still compatible with the recent GERDA limit as well as the individual ${}^{136}\mathrm{Xe}$ limits for a few NME calculations, it is inconsistent with the combined ${}^{136}\mathrm{Xe}$ limit for all but one NME. Imposing the most stringent limit from Planck, we find that the canonical light neutrino contribution cannot saturate the current limit, irrespective of the NME uncertainties. Saturation can be reached by inclusion of the right-handed (RH) neutrino contributions in TeV-scale left-right symmetric models with type-II seesaw. This imposes a lower limit on the lightest neutrino mass. Using the $0\nu \beta \beta$ bounds, we also derive correlated constraints in the RH sector, complimentary to those from direct searches at the LHC.

Massive gravity provides a holographic model for theories exhibiting momentum dissipation. We provide an analytic expression for the DC conductivity. The result is universal, depending only on properties of the infrared horizon, and holds at finite temperature and charge density. In addition, we provide a derivation of black hole thermodynamics in holographic massive gravity and show that the resulting physics is sensible.

We investigate the nature of the finite-temperature chiral transition in QCD with two light flavors, in the case of an effective suppression of the $\mathrm{U}(1{)}_A$ symmetry breaking induced by the axial anomaly, which implies the symmetry breaking $\mathrm{U}(2{)}_L\otimes \mathrm{U}(2{)}_R\to \mathrm{U}(2{)}_V$, instead of $\mathrm{SU}(2{)}_L\otimes \mathrm{SU}(2{)}_R\to \mathrm{SU}(2{)}_V$. For this purpose, we perform a high-order field-theoretical perturbative study of the renormalization-group flow of the corresponding three-dimensional multiparameter Landau-Ginzburg-Wilson ${\Phi }^4$ theory with the same symmetry-breaking pattern. We confirm the existence of a stable fixed point and determine its attraction domain in the space of the bare quartic parameters. Therefore, the chiral QCD transition might be continuous also if the $\mathrm{U}(1{)}_A$ symmetry is effectively restored at $T_c$. However, the corresponding universality class differs from the O(4) vector universality class which would describe a continuous transition in the presence of a substantial $\mathrm{U}(1{)}_A$ symmetry breaking at $T_c$. We estimate the critical exponents of the $\mathrm{U}(2{)}_L\otimes \mathrm{U}(2{)}_R\to \mathrm{U}(2{)}_V$ universality class by computing and analyzing the corresponding perturbative expansions. These results are important to discriminate among the different scenarios for the scaling behavior of QCD with two light flavors close to the chiral transition.

Quantum effects due to conformal matter in a black hole background result in universal logarithmic corrections to black-hole entropy. The universality resides in the connection of the log term coefficient with those of type-A and type-B Weyl anomalies, regularization-scheme independent quantities. We presently study the case of extremal black holes within Wald’s Noether charge formalism. In the conformal class of flat metrics, we are again able to unveil the log term in the entropy from the horizon value of the solution to the $Q$-curvature uniformization problem. Beyond conformally flat backgrounds, type-B Weyl anomaly becomes an obstruction to considering flat space as the fiducial metric and the search for a metric of constant $Q$-curvature remains open. Notwithstanding, by a uniform scaling argument we show that the results based on heat kernel and Euclidean computations (namely entropy function and conical defect) can also be derived as Wald entropy, that is, as Noether charge of the integrated anomaly or conformal index. We finally comment on the relation with entanglement entropy.

We develop an adiabatic formalism to study the Hawking phenomenon from the perspective of Unruh-DeWitt detectors moving along nonstationary, nonasymptotic trajectories. When applied to geodesic trajectories, this formalism yields the following results: (i) though they have zero acceleration, the temperature measured by detectors on circular orbits is higher than that measured by static detectors at the same distance from the hole, and diverges on the photon sphere, (ii) in the near-horizon region, both outgoing and incoming modes excite infalling detectors, and, for highly bound trajectories ($E\ll 1$), the latter actually dominate the former. We confirm the apparent perception of high-temperature Hawking radiation by infalling observers with $E\ll 1$ by showing that the energy flux measured by these observers diverges in the $E\to 0$ limit. We close with a discussion of the role played by spacetime curvature on the near-horizon Hawking radiation.

We propose an extra-dimensional mechanism that adequately suppresses the rate of proton decay mediated by the $X$ bosons in grand unified theories. The $X$ bosons and their Kaluza-Klein modes are localized in the extra spatial dimensions due to the kink configuration of the adjoint Higgs multiplet that is responsible for the spontaneous breaking of the unified gauge group while the standard model gauge bosons freely propagate in the bulk. By localizing fermion multiplets apart from the $X$ bosons in the extra dimensions, the resulting four-dimensional couplings that give rise to proton decay are exponentially suppressed, leading to the longevity of the proton even when the mass scale of the $X$ bosons is much lower than the usual unification scale.

We have examined TeV scale effects of extra spatial dimensions through the processes $\gamma q\to \gamma q$, where $q=u$, $d$, $c$, $s$, $b$, $\overline{u}$, $\overline{d}$, $\overline{c}$, $\overline{s}$, $\overline{b}$. These processes have been treated in a photon-proton collision via the main reaction $pp\to p\gamma p\to p\gamma qX$ at the LHC. We have employed the equivalent photon approximation for incoming photon beams and performed statistical analysis for various forward detector acceptances.

The possibility of the $0^{+}$ $\eta \eta$ resonance $f_0(2100)$ as a candidate of the $Q^2{\overline{Q}}^2$ state $C^{ss}(36)$ is explored. The $\eta \eta$ channel of $f_0(2100)$ is the dominant decay mode; the $\eta {\eta }^{\prime }$ channel has less decay rate; the decay rate of the ${\eta }^{\prime }{\eta }^{\prime }$ channel is very small. The $\pi \pi$, $K\overline{K}$, $4\pi$ modes are at next leading order in $N_C$ expansion. Other possible decay modes are discussed.

We study the space-time structure of polynomiality and positivity—the most important properties which are inherent to the generalized parton distributions (GPDs). In this connection, we reexamine the issue of the time and normal ordering in the operator definition of GPDs. We demonstrate that the contribution of the anticommutator matrix element in the collinear kinematics, which was previously argued to vanish, has to be added in order to satisfy the polynomiality condition. Furthermore, we schematically show that a new contribution due to the anticommutator modifies likewise the so-called positivity constraint, i.e., the Cauchy-Bunyakovsky-Schwarz inequality, which is another important feature of the GPDs.

We investigate the future evolution of the Nariai black hole, which is the extremal limit of the Schwarzschild–de Sitter one in modified gravity. The perturbation equations around the Nariai black hole are derived in static and cosmological patches for general $F(R)$ gravity. The analytical and numerical study of several realistic $F(R)$ models shows the occurrence of a rich variety of scenarios: instabilities, celebrated Hawking evaporation, and anti-evaporation of black holes. The realization of a specific scenario depends on the model under consideration. It is remarkable that the presence of such primordial black holes in the current Universe may indicate modified gravity, which supports the anti-evaporation as the preferable model. As a generalization, we extend the study of the Nariai black hole evolution to modified Gauss-Bonnet gravity. The corresponding perturbation equations turn out to be much more complicated than in the case of $F(R)$ gravity. For a specific example of modified Gauss-Bonnet gravity, we demonstrate that the Nariai solution may be stable.

It is possible to dualize theories based on deformed dispersion relations and Einstein gravity so as to map them into theories with trivial dispersion relations and rainbow gravity. This often leads to “dual inflation” without the usual breaking of the strong energy condition. We identify the dispersion relations in the original frame which map into “intermediate” inflationary models. These turn out to be particularly simple: power-laws modulated by powers of a logarithm. The fluctuations predicted by these scenarios are near, but not exactly scale-invariant, with a red running spectral index. These dispersion relations deserve further study within the context of quantum gravity and the phenomenon of dimensional reduction in the ultraviolet.

We adopt a framework where quantum gravity’s dynamical dimensional reduction of spacetime at short distances is described in terms of modified dispersion relations. We observe that by subjecting such models to a momentum-space diffeomorphism one obtains a “dual picture” with unmodified dispersion relations, but a modified measure of integration over momenta. We then find that the UV Hausdorff dimension of momentum space which can be inferred from this modified integration measure coincides with the short-distance spectral dimension of spacetime. This result sheds light into why scale-invariant fluctuations are obtained if the original model for two UV spectral dimensions is combined with Einstein gravity. By studying the properties of the inner product we derive the result that it is only in two energy-momentum dimensions that microphysical vacuum fluctuations are scale invariant. This is true ignoring gravity, but then we find that if Einstein gravity is postulated in the original frame, in the dual picture gravity switches off, since all matter becomes conformally coupled. We argue that our findings imply that the following concepts are closely connected: scale invariance of vacuum quantum fluctuations, conformal invariance of the gravitational coupling, UV reduction to spectral dimension two in position space, and UV reduction to Hausdorff dimension two in energy-momentum space.

Axionlike particles (ALPs) are hypothetical light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of ALPs can modify the energy spectrum of the gamma rays for a sufficiently large coupling between ALPs and photons. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac object PKS $2155-304$ ($z=0.116$) are used to derive upper limits at the 95% C.L. on the strength of the ALP coupling to photons, $g_{\gamma a}<2.1\times {10}^{-11}\mathrm{Ge}{\mathrm{V}}^{-1}$ for an ALP mass between 15 and 60 neV. The results depend on assumptions on the magnetic field around the source, which are chosen conservatively. The derived constraints apply to both light pseudoscalar and scalar bosons that couple to the electromagnetic field.

Nonthermal cosmological histories are capable of greatly increasing the available parameter space of different particle physics dark matter (DM) models and are well motivated by the ubiquity of late-decaying gravitationally coupled scalars in UV theories like string theory. A nonthermal DM model is presented in the context of LARGE Volume Scenarios in type IIB string theory. The model is capable of addressing both the moduli-induced gravitino problem as well as the problem of overproduction of axionic dark radiation and/or DM. We show that the right abundance of neutralino DM can be obtained in both thermal under and overproduction cases for DM masses between $\mathcal{O}(\mathrm{GeV})$ and $\mathcal{O}(\mathrm{TeV})$. In the latter case the contribution of the QCD axion to the relic density is totally negligible, while in the former case it can be comparable to that of the neutralino thus resulting in a multicomponent DM scenario.

Compared to the other neutrino mixing angles ${\theta }_{13}$ is small. The solar mass splitting is about two orders smaller than the atmospheric splitting. We show that both could arise from a perturbation of a more symmetric structure. The perturbation also affects the solar mixing angle and can make alternate mixing patterns such as tribimaximal, bimaximal, or other variants equally viable. For real perturbations this can be accomplished only for normal mass ordering with the lightest neutrino mass less than ${10}^{-2}\mathrm{eV}$. Both mass orderings can be accommodated by going over to complex perturbations if the lightest neutrino is heavier. The $CP$-phase in the lepton sector, fixed by ${\theta }_{13}$ and the lightest neutrino mass, distinguishes between different mixing models.

We study temperature and finite-size effects on the spontaneous symmetry breaking/restoration for a scalar field model under the influence of an external magnetic field, at finite chemical potential. We use the two-particle irreducible formalism and consider the large-$N$ limit. We find that there is a minimal size of the system to sustain the broken phase, which diminishes as the applied field increases but is independent of the chemical potential. We analyze the critical curves and show that the magnetic field enhances the broken-phase regions, while increasing the chemical potential leads to a diminishment of the critical temperature.

We consider rectangular Wilson loops in certain nonequilibrium quantum states in $\mathcal{N}=4$ super Yang-Mills theory at weak coupling, prepared with a quantum quench. We find that in the ladder approximation, the Bethe-Salpeter equation can be reduced to solving a massive $1+1$ dimensional wave equation with a leaking boundary condition leading to a quasinormal behavior analogous to what is found in studying dynamics of fields in black hole backgrounds. Furthermore, we find that the Wilson loops with size $L$ approach a thermal form after time $T\approx L/2$. The thermal form found in the current paper follows from the particular initial state chosen.

This paper discusses phenomena close to the critical QCD temperature, using the holographic model. One issue studied is the overcooled high-$T$ phase, in which we calculate quasinormal sound modes. We do not find instabilities associated with other first-order phase transitions, but nevertheless observe drastic changes in sound propagation and dissipation. The rest of the paper considers a cluster of the high-$T$ phase in the UV in coexistence with the low-$T$ phase, in a simplified ansatz in which the wall separating them is positioned only in the holographic coordinate. This allows one to find the force on the wall and classical motion of the cluster. When classical motion is forbidden, we evaluate the tunneling probability through the remaining barrier.

We present the decomposition of QCD partial amplitudes into primitive amplitudes at one-loop level and tree level for arbitrary numbers of quarks and gluons. Our method is based on shuffle relations. This method is purely combinatorial and does not require the inversion of a system of linear equations.

We study for the first time a three-dimensional octahedron constellation for a space-based gravitational wave detector, which we call the octahedral gravitational observatory (OGO). With six spacecraft the constellation is able to remove laser frequency noise and acceleration disturbances from the gravitational wave signal without needing LISA-like drag-free control, thereby simplifying the payloads and placing less stringent demands on the thrusters. We generalize LISA’s time-delay interferometry to displacement-noise free interferometry (DFI) by deriving a set of generators for those combinations of the data streams that cancel laser and acceleration noise. However, the three-dimensional configuration makes orbit selection complicated. So far, only a halo orbit near the Lagrangian point L1 has been found to be stable enough, and this allows only short arms up to 1400 km. We derive the sensitivity curve of OGO with this arm length, resulting in a peak sensitivity of about $2\times {10}^{-23}{\mathrm{Hz}}^{-1/2}$ near 100 Hz. We compare this version of OGO to the present generation of ground-based detectors and to some future detectors. We also investigate the scientific potentials of such a detector, which include observing gravitational waves from compact binary coalescences, the stochastic background, and pulsars as well as the possibility to test alternative theories of gravity. We find a mediocre performance level for this short arm length detector, between those of initial and advanced ground-based detectors. Thus, actually building a space-based detector of this specific configuration does not seem very efficient. However, when alternative orbits that allow for longer detector arms can be found, a detector with much improved science output could be constructed using the octahedron configuration and DFI solutions demonstrated in this paper. Also, since the sensitivity of a DFI detector is limited mainly by shot noise, we discuss how the overall sensitivity could be improved by using advanced technologies that reduce this particular noise source.