In this work, we study the $\mathcal{P}\mathcal{T}$-symmetric ($i{\varphi }^3$) theory using the effective action formalism. To test the accuracy of the used technique, we apply it first to the $\mathcal{P}\mathcal{T}$-symmetric ($-{\varphi }^4$) theory, where we reproduce the same results obtained in the literature using the method of Dyson-Schwinger equations. In $0+1$ space-time dimensions, the one-loop effective potential prediction for the ($i{\varphi }^3$) theory ought to be more accurate than WKB results. The effective potential for the massless $\mathcal{P}\mathcal{T}$-symmetric ($i{\varphi }^3$) model is shown to be bounded from below, which is the first analytic result that advocates the vacuum stability of this theory. Our calculations show that the massless theory possesses only one stable vacuum as in the literature, but for the massive theory we find that there exist two stable vacua. For a nonzero magnetic field, we show that the $\mathcal{P}\mathcal{T}$-symmetry of the theory is broken for negative imaginary magnetic field, which agrees with the Lee-Yang theorem. We argue that $\mathcal{P}\mathcal{T}$-symmetry breaking is a manifestation of the Yang-Lee edge singularity.

We show that four-dimensional black holes become stable below a certain mass when the Einstein-Hilbert action is supplemented with higher-curvature terms. We prove this to be the case for an infinite family of ghost-free theories involving terms of arbitrarily high order in curvature. The new black holes, which are nonhairy generalizations of Schwarzschild’s solution, present a universal thermodynamic behavior for general values of the higher-order couplings. In particular, small black holes have infinite lifetimes. When the evaporation process makes the semiclassical approximation break down (something that occurs after a time which is usually infinite for all practical purposes), the resulting object retains a huge entropy, in stark contrast with Schwarzschild’s case.

We analytically study the nonlinear stability of a spherically symmetric wormhole supported by an infinitesimally thin brane of negative tension, which has been devised by Barcelo and Visser. We consider a situation in which a thin spherical shell composed of dust falls into an initially static wormhole; the dust shell plays the role of the nonlinear disturbance. The self-gravity of the falling dust shell is completely taken into account through Israel’s formalism of the metric junction. When the dust shell goes through the wormhole, it necessarily collides with the brane supporting the wormhole. We assume the interaction between these shells is only gravity and show the condition under which the wormhole stably persists after the dust shell goes through it.

We introduce a quasidilaton scalar field to the minimal theory of massive gravity with the Minkowski fiducial metric, in such a way that the quasidilaton global symmetry is maintained and that the theory admits a stable self-accelerating de Sitter solution. We start with a precursor theory that contains three propagating gravitational degrees of freedom without a quasidilaton scalar and introduce Stückelberg fields to covariantize its action. This makes it possible for us to formulate the quasidilaton global symmetry that mixes the Stückelberg fields and the quasidilaton scalar field. By the Hamiltonian analysis we confirm that the precursor theory with the quasidilaton scalar contains 4 degrees of freedom, three from the precursor massive gravity and one from the quasidilaton scalar. We further remove one propagating degree of freedom to construct the minimal quasidilaton theory with three propagating degrees of freedom, corresponding to two polarizations of gravitational waves from the minimal theory of massive gravity and one scalar from the quasidilaton field, by carefully introducing two additional constraints to the system in the Hamiltonian language. Switching to the Lagrangian language, we find self-accelerating de Sitter solutions in the minimal quasidilaton theory and analyze their stability. It is found that the self-accelerating de Sitter solution is stable in a wide range of parameters.

We present the results of 14 simulations of nonspinning black hole binaries with mass ratios $q=m_1/m_2$ in the range $1/100\le q\le 1$. For each of these simulations we perform three runs at increasing resolution to assess the finite difference errors and to extrapolate the results to infinite resolution. For $q\ge 1/6$, we follow the evolution of the binary typically for the last ten orbits prior to merger. By fitting the results of these simulations, we accurately model the peak luminosity, peak waveform frequency and amplitude, and the recoil of the remnant hole for unequal-mass nonspinning binaries. We verify the accuracy of these new models and compare them to previously existing empirical formulas. These new fits provide a basis for a hierarchical approach to produce more accurate remnant formulas in the generic precessing case. They also provide input to gravitational waveform modeling.

We investigate cosmic string networks in the Abelian Higgs model using data from a campaign of large-scale numerical simulations on lattices of up to $4096^3$ grid points. We observe scaling or self-similarity of the networks over a wide range of scales and estimate the asymptotic values of the mean string separation in horizon length units $\dot{\xi }$ and of the mean square string velocity ${\overline{v}}^2$ in the continuum and large time limits. The scaling occurs because the strings lose energy into classical radiation of the scalar and gauge fields of the Abelian Higgs model. We quantify the energy loss with a dimensionless radiative efficiency parameter and show that it does not vary significantly with lattice spacing or string separation. This implies that the radiative energy loss underlying the scaling behavior is not a lattice artifact, and justifies the extrapolation of measured network properties to large times for computations of cosmological perturbations. We also show that the core growth method, which increases the defect core width with time to extend the dynamic range of simulations, does not introduce significant systematic error. We compare $\dot{\xi }$ and ${\overline{v}}^2$ to values measured in simulations using the Nambu-Goto approximation, finding that the latter underestimate the mean string separation by about 25%, and overestimate ${\overline{v}}^2$ by about 10%. The scaling of the string separation implies that string loops decay by the emission of massive radiation within a Hubble time in field theory simulations, in contrast to the Nambu-Goto scenario which neglects this energy loss mechanism. String loops surviving for only one Hubble time emit much less gravitational radiation than in the Nambu-Goto scenario and are consequently subject to much weaker gravitational wave constraints on their tension.

We introduce fully SUSic grand unified theories (SGUTs), supersymmetry (SUSY) grand unified theories that, upon symmetry breaking through the Higgs mechanism, decompose into a visible sector and an extra sector where the dynamics of the extra sector gauge group is responsible for SUSY breaking. Fully SGUTs thus have the important feature that all gauge groups of the visible sector and the extra sector unify into a simple gauge group at the SGUT scale, therefore generalizing the successful minimal SUSic Standard Model (MSSM) gauge coupling unification to all the gauge couplings of the theory. By focusing on the Intriligator, Seiberg, and Shih (ISS) SUSY-breaking mechanism in the extra sector, we show that it is impossible to reproduce the MSSM matter content when there exists a metastable ISS SUSY-breaking state.

We compute the weak magnetic field correction to the four-point quark-gluon vertex at finite temperature and chemical potential within the hard thermal loop approximation. The resulting four-point quark-gluon vertex satisfies the Ward identity with the three-point quark-gluon vertex.

The recent observation of two hidden-charm pentaquark states by LHCb collaborations prompted us to investigate the exotic states close to the $\overline{D}{\mathrm{\Lambda }}_{\mathrm{c}}$, ${\overline{D}}^{*}{\mathrm{\Lambda }}_{\mathrm{c}}$, $\overline{D}{\mathrm{\Sigma }}_{\mathrm{c}}$, $\overline{D}{\mathrm{\Sigma }}_{\mathrm{c}}^{*}$, ${\overline{D}}^{*}{\mathrm{\Sigma }}_{\mathrm{c}}$ and ${\overline{D}}^{*}{\mathrm{\Sigma }}_{\mathrm{c}}^{*}$ thresholds. We therefore studied the hadronic molecules that form the coupled-channel system of ${\overline{D}}^{(*)}{\mathrm{\Lambda }}_{\mathrm{c}}$ and ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_{\mathrm{c}}^{(*)}$. As the heavy quark spin symmetry manifests the mass degenerations of $\overline{D}$ and ${\overline{D}}^{*}$ mesons, and of ${\mathrm{\Sigma }}_{\mathrm{c}}$ and ${\mathrm{\Sigma }}_{\mathrm{c}}^{*}$ baryons, the coupled channels of ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_{\mathrm{c}}^{(*)}$ are important in these molecules. In addition, we consider the coupling to the ${\overline{D}}^{(*)}{\mathrm{\Lambda }}_{\mathrm{c}}$ channel whose thresholds are near the ${\overline{D}}^{(*)}{\mathrm{\Sigma }}_{\mathrm{c}}^{(*)}$ thresholds, and the coupling to the state with nonzero orbital angular momentum mixed by the tensor force. This full coupled-channel analysis of ${\overline{D}}^{(*)}{\mathrm{\Lambda }}_{\mathrm{c}}-{\overline{D}}^{(*)}{\mathrm{\Sigma }}_{\mathrm{c}}^{(*)}$ with larger orbital angular momentum has never been performed before. By solving the coupled-channel Schrödinger equations with the one meson exchange potentials with respect to the heavy quark spin and chiral symmetries, we studied the hidden-charm hadronic molecules with $I(J^P)=1/2(3/2^{\pm })$ and $1/2(5/2^{\pm })$. We conclude that the $J^P$ assignment of the observed pentaquarks is $3/2^{+}$ for $P_{\mathrm{c}}^{+}(4380)$ and $5/2^{-}$ for $P_{\mathrm{c}}^{+}(4450)$, which is in agreement with the results of the LHCb analysis. In addition, we give predictions for other $J^P=3/2^{\pm }$ states at 4136.0, 4307.9 and 4348.7 MeV in $J^P=3/2^{-}$, and 4206.7 MeV in $J^P=3/2^{+}$, which can be further investigated by means of experiment.

We extend the two-flavor hard-wall holographic model of Erlich, Katz, Son, and Stephanov [Phys. Rev. Lett. 95, 261602 (2005)] to four flavors to incorporate strange and charm quarks. The model incorporates chiral and flavor symmetry breaking and provides a reasonable description of masses and weak decay constants of a variety of scalar, pseudoscalar, vector, and axial-vector strange and charmed mesons. In particular, we examine flavor symmetry breaking in the strong couplings of the $\rho$ meson to the charmed $D$ and $D^{*}$ mesons. We also compute electromagnetic form factors of the $\pi$, $\rho$, $K$, $K^{*}$, $D$ and $D^{*}$ mesons. We compare our results for the $D$ and $D^{*}$ mesons with lattice QCD data and other nonperturbative approaches.

We investigate properties of the ground state of a light-quark matter with heavy-quark impurities. This system exhibits the “QCD Kondo effect” where the interaction strength between a light quark near the Fermi surface and a heavy quark increases with decreasing energy of the light quark toward the Fermi energy and diverges at some scale near the Fermi energy, called the Kondo scale. Around and below the Kondo scale, we must treat the dynamics nonperturbatively. As a typical nonperturbative method to treat the strong coupling regime, we adopt a mean-field approach where we introduce a condensate, the Kondo condensate, representing a mixing between a light quark and a heavy quark, and determine the ground state in the presence of the Kondo condensate. We show that the ground state is a topologically nontrivial state and the heavy-quark spin forms the hedgehog configuration in the momentum space. We can define the Berry phase for the ground-state wave function in the momentum space, which is associated with a monopole at the position of a heavy quark. We also investigate fluctuations around the mean field in the random-phase approximation and show the existence of (excitonlike) collective excitations made of a hole $h$ of a light quark and a heavy quark $Q$.

We present a new procedure to determine parton distribution functions (PDFs), based on Markov chain Monte Carlo (MCMC) methods. The aim of this paper is to show that we can replace the standard ${\chi }^2$ minimization by procedures grounded on statistical methods, and on Bayesian inference in particular, thus offering additional insight into the rich field of PDFs determination. After a basic introduction to these techniques, we introduce the algorithm we have chosen to implement—namely Hybrid (or Hamiltonian) Monte Carlo. This algorithm, initially developed for Lattice QCD, turns out to be very interesting when applied to PDFs determination by global analyses; we show that it allows us to circumvent the difficulties due to the high dimensionality of the problem, in particular concerning the acceptance. A first feasibility study is performed and presented, which indicates that Markov chain Monte Carlo can successfully be applied to the extraction of PDFs and of their uncertainties.

From the point of view of elementary particle physics, the gravitational constant $G$ is extraordinarily small. This has led to asking whether it could have decayed to its present value from an initial one commensurate with microscopical units. A mechanism that leads to such a decay is proposed herein. It is based on assuming that $G$ may take different values within regions of the universe separated by a novel kind of domain wall, a “$G$-wall.” The idea is implemented by introducing a gauge potential $A_{\mu \nu \rho }$, and its conjugate $D$, which determines the value of $G$ as an integration constant rather than a fundamental constant. The value of $G$ jumps when one goes through a $G$-wall. The procedure extends one previously developed for the cosmological constant, but the generalization is far from straightforward: (i) The intrinsic geometry of a $G$-wall is not the same as seen from its two sides because the second law of black hole thermodynamics mandates that the jump in $G$ must cause a discontinuity in the scale of length. (ii) The size of the decay step in $G$ is controlled by a function $G(D)$ which may be chosen so as to diminish the value of $G$ towards the asymptote $G=0$. It is shown that: (i) The dynamics of the gravitational field with $G$ treated as a dynamical variable, coupled to $G$-walls and matter, follows from an action principle, which is given. (ii) A particle that impinges on a $G$-wall may be refracted or reflected. (iii) The various forces between two particles change when a $G$-wall is inserted in between them. (iv) $G$-walls may be nucleated trough tunneling and thermal effects, whose semiclassical probabilities are evaluated. (v) If the action principle is constructed properly, the entropy of a black hole increases when the value of the gravitational constant is changed through the absorption of a G-wall by the hole.

We consider generalized Galileon theories within general relativity in four-dimensional spacetime. We provide the argument showing that the generalized Galileons described by a wide class of Lagrangians do not admit stable, static, spherically symmetric semiclosed worlds. We also show that in a class of theories with $p_{\perp }=-\rho$ (where $p_{\perp }$ is transverse pressure and $\rho$ is energy density), semiclosed worlds, if they exist, would be observed as objects of negative mass.

In this work, we investigate the preheating mechanism in a disformally coupled inflationary model where the scalar field $\varphi$ (which is the inflaton field) naturally coupled to another matter field $\chi$ induced by the disformal transformation. In the present scenario, novel derivative interactions mixing the kinetic terms of the two fields emerge inherently. We start by deriving the evolution of the background system when the backreaction on the background field is neglected. We examine the particle production due to parametric resonances in the models and find in Minkowski space that the stage of parametric resonances can be described by the Mathieu equation. Interestingly, we discover that broad resonances in our models can be typically achieved. Finally, we compare our results with the previously studied model with derivative couplings.

Because of a low mechanical loss, thin films made of silicon nitride (${\mathrm{Si}}_3{\mathrm{N}}_4$) are interesting for fundamental research and development in the field of gravitational-wave detection. ${\mathrm{Si}}_3{\mathrm{N}}_4$ membranes allow for the characterization of quantum radiation pressure noise (RPN), which will be a limiting noise source in gravitational-wave detectors of the second and third generations. Furthermore, ${\mathrm{Si}}_3{\mathrm{N}}_4$ is an interesting material for possible thermal noise reduction in highly reflective mirror coatings. For both applications, the optical absorption of ${\mathrm{Si}}_3{\mathrm{N}}_4$ needs to be low. This paper presents absorption measurements on low-stress ${\mathrm{Si}}_3{\mathrm{N}}_4$ membranes showing an absorption a factor of 7 lower at 1550 nm than at 1064 nm resulting in an estimated 2 times higher sensitivity in RPN experiments at the higher wavelength and making ${\mathrm{Si}}_3{\mathrm{N}}_4$ an interesting material for highly reflective multimaterial mirror coatings at 1550 nm.

A study of single top quark production via flavor changing neutral current interactions at $tq\gamma$ vertices is performed at the future circular hadron electron collider. The signal cross sections for the processes $e^{-}p\to e^{-}{W}^{\pm }q+X$ and $e^{-}p\to e^{-}{W}^{\pm }bq+X$ in the collision of an electron beam with energy $E_e=60\mathrm{GeV}$ and a proton beam with energy $E_p=50\mathrm{TeV}$ are calculated. In the analysis, the invariant mass distributions of three jets reconstructing top quark mass, requiring one b-tagged jet and two other jets reconstructing the $W$ mass are used to count signal and background events after all selection cuts. The upper limits on the anomalous flavor changing neutral current $tq\gamma$ couplings are found to be ${\lambda }_q<0.01$ at the future circular hadron electron collider for $L_{\mathrm{int}}=100{\mathrm{fb}}^{-1}$ with the fast simulation of detector effects. Signal significance depending on the couplings ${\lambda }_q$ is analyzed and an enhanced sensitivity is found to the branching ratio $\mathrm{BR}(t\to q\gamma )$ at the future circular hadron electron collider when compared to the current experimental results.

The standard model (SM) prediction for the $CP$-violating quantity ${\epsilon }_K^{\prime }/{\epsilon }_K$ deviates from its measured value by $2.8\sigma$. It has been shown that this tension can be resolved within the minimal supersymmetric standard model (MSSM) through gluino-squark box diagrams, even if squarks and gluinos are much heavier than 1 TeV. The rare decays $K_L\to {\pi }^0\nu \overline{\nu }$ and $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ are similarly sensitive to very high mass scales and the first one also measures $CP$ violation. In this article, we analyze the correlations between ${\epsilon }_K^{\prime }/{\epsilon }_K$ and $\mathcal{B}(K_L\to {\pi }^0\nu \overline{\nu })$ and $\mathcal{B}(K^{+}\to {\pi }^{+}\nu \overline{\nu })$ within the MSSM aiming at an explanation of ${\epsilon }_K^{\prime }/{\epsilon }_K$ via gluino-squark box diagrams. The dominant MSSM contribution to the $K\to \pi \nu \overline{\nu }$ branching fractions stems from box diagrams with squarks, sleptons, charginos, and neutralinos, and the pattern of the correlations is different from the widely studied $Z$-penguin scenarios. This is interesting in light of future precision measurements by KOTO and NA62 at J-PARC and CERN, respectively. We find $\mathcal{B}(K_L\to {\pi }^0\nu \overline{\nu })/{\mathcal{B}}^{\mathrm{SM}}(K_L\to {\pi }^0\nu \overline{\nu })\lesssim 2(1.2)$ and $\mathcal{B}(K^{+}\to {\pi }^{+}\nu \overline{\nu })/{\mathcal{B}}^{\mathrm{SM}}(K^{+}\to {\pi }^{+}\nu \overline{\nu })\lesssim 1.4(1.1)$, if all squark masses are above 1.5 TeV, gaugino masses obey GUT relations, and if one allows for a fine-tuning at the 1%(10%) level for the gluino mass. Larger values are possible for a tuned $CP$ violating phase. Furthermore, the sign of the MSSM contribution to ${\epsilon }_K^{\prime }$ imposes a strict correlation between $\mathcal{B}(K_L\to {\pi }^0\nu \overline{\nu })$ and the hierarchy between the masses $m_{\overline{U}}$, $m_{\overline{D}}$ of the right-handed up-squark and down-squark: $\mathrm{sgn}[\mathcal{B}(K_L\to {\pi }^0\nu \overline{\nu })-{\mathcal{B}}^{\mathrm{SM}}(K_L\to {\pi }^0\nu \overline{\nu })]=\mathrm{sgn}(m_{\overline{U}}-m_{\overline{D}})$.

The energy-momentum tensor plays an important role in QCD thermodynamics. Its expectation value contains information of the pressure and the energy density as its diagonal part. Further properties like viscosity and specific heat can be extracted from its correlation function. A nonperturbative evaluation of it on the lattice is called. Recently, a new method based on the gradient flow was introduced to calculate the energy-momentum tensor on the lattice and has been successfully applied to quenched QCD. In this paper, we apply the gradient flow method to calculate the energy-momentum tensor in ($2+1$)-flavor QCD adopting a nonperturbatively $O(a)$-improved Wilson quark action and the renormalization group-improved Iwasaki gauge action. As the first application of the method with dynamical quarks, we study at a single but fine lattice spacing $a\simeq 0.07\mathrm{fm}$ with heavy $u$ and $d$ quarks ($m_{\pi }/m_{\rho }\simeq 0.63$) and approximately physical $s$ quark ($m_{{\eta }_{ss}}/m_{\varphi }\simeq 0.74$). With the fixed-scale approach, temperature is varied by the temporal lattice size $N_t$ at a fixed lattice spacing. Performing simulations on lattices with $N_t=16$ to 4, the temperature range of $T\simeq 174–697\mathrm{MeV}$ is covered. We find that the results of the pressure and the energy density by the gradient flow method are consistent with the previous results using the $T$-integration method at $T\lesssim 280\mathrm{MeV}$ ($N_t\gtrsim 10$), while the results show disagreement at $T\gtrsim 350\mathrm{MeV}$ ($N_t\lesssim 8$), presumably due to the small-$N_t$ lattice artifact of $O((aT{)}^2)=O(1/N_t^2)$. We also apply the gradient flow method to evaluate the chiral condensate taking advantage of the gradient flow method that renormalized quantities can be directly computed avoiding the difficulty of explicit chiral violation with lattice quarks. We compute the renormalized chiral condensate in the $\overline{\mathrm{MS}}$ scheme at renormalization scale $\mu =2\mathrm{GeV}$ with a high precision to study the temperature dependence of the chiral condensate and its disconnected susceptibility. Even with the Wilson-type quark action which violates the chiral symmetry explicitly, we obtain the chiral condensate and its disconnected susceptibility showing a clear signal of pseudocritical temperature at $T\sim 190\mathrm{MeV}$ related to the chiral restoration crossover.

We investigated the possibility that the lightest pentaquark state recently reported by the $LH{C}_b$ Collaboration [R. Aaij et al., Phys. Rev. Lett. 115, 072001 (2015); 117, 082002 (2016); 117, 082003 (2016)], $P_c^{+}(4380)$, could be described as a compact pentaquark state. By using very general arguments, dictated by symmetry considerations, we described the pentaquark states within a group theory approach. A complete classification of all possible states and quantum numbers, which can be useful both to the experimentalists in their search for new findings and to theoretical model builders, is given, without introducing any particular dynamical model. Some predictions are provided by means of a Gürsey-Radicati inspired mass formula. We have reproduced the mass and the quantum numbers of the lightest pentaquark state reported by $LH{C}_b$, $P_c^{+}(4380)$, and have predicted other pentaquark resonances which belong to the same multiplet as the lightest one. Having calculated the masses of these resonances, we suggest possible bottom baryon decay channels which involve the predicted resonances as intermediate states. Finally, we have computed the partial decay widths for all the predicted pentaquark resonances.