We study the network of Type-I cosmic strings using the field-theoretic numerical simulations in the Abelian-Higgs model. For Type-I strings, the gauge field plays an important role, and thus we find that the correlation length of the strings is strongly dependent upon the parameter $\beta$, the ratio between the masses of the scalar field and the gauge field, namely, $\beta =m_{\phi }^2/m_A^2$. In particular, if we take the cosmic expansion into account, the network becomes densest in the comoving box for a specific value of $\beta$ for $\beta <1$.

The inflationary paradigm provides a mechanism to generate the primordial perturbations needed to explain the observed large-scale structures in the Universe. Inflation traces back all the inhomogeneities to quantum fluctuations although the structures look classical today. The squeezing of primordial quantum fluctuations along with the mechanism of decoherence accounts for many aspects of this quantum-to-classical transition, although it remains a matter of debate as to whether this is sufficient to explain the issue of the realization of a single outcome (i.e. the issue of macro-objectification) from a quantum ensemble given that the Universe is a closed system. A similar question of the emergence of classical behavior of macroscopic objects exists also for laboratory systems and apart from decoherence there have been attempts to resolve this issue through continuous spontaneous localization (CSL), which is a stochastic nonlinear modification of the nonrelativistic Schrödinger equation. Recently, Martin et al. have investigated whether a CSL-like mechanism with a constant strength parameter—when the Mukhanov-Sasaki variable is taken as the “collapse operator”—can explain how the primordial quantum perturbations generated during inflation become classical. Within the scope of their assumptions they essentially come to a negative conclusion. In the present work, we generalize their analysis by allowing the CSL strength parameter to depend on physical scales so as to capture the CSL amplification mechanism. We show that such a generalization provides a mechanism for the macro-objectification (i.e. classicalization) of the inflationary quantum perturbations, while also preserving the scale invariance of the power spectrum and the phase coherence of superhorizon perturbation modes in a particular class of these models.

The functional renormalization group equation is expanded to a two-loop form. This two-loop form equation involves one-loop effective action. An intermediate effective action perspective is adopted toward the one-loop effective action. That is to say, the intermediate effective action could not be of the same form of the bare action and one can make an ansatz to it. Thus by focusing on different high-dimensional operators, effects of the chosen operators can be investigated. QCD through intermediate 4-fermion interactions is investigated. Of the six kinds of 4-fermion interactions generated by one-loop QCD, four kinds generate fermion mass while the other two kinds decrease it. Flow patterns on the ${\tilde{m}}_{\mathrm{phys}}^2-{\tilde{g}}^2$ plane are drawn.

We reexamine the quantization of structure constants, or equivalently the choice of lattice in the so-called flat group reductions, introduced originally by Scherk and Schwarz. Depending on this choice, the vacuum either breaks supersymmetry (SUSY) and lifts certain moduli, or preserves all supercharges and is identical to the one obtained from the torus reduction. Nonetheless the low-energy effective theory proposed originally by Scherk and Schwarz is a gauged supergravity that describes SUSY breaking and moduli lifting for all values of the structure constants. When the vacuum does not break SUSY, such a description turns out to be an artifact of the consistent truncation to left-invariant forms as illustrated in the example of ISO(2). We furthermore discuss the construction of flat groups in $d$ dimensions and find that the Scherk-Schwarz algorithm is exhaustive. A classification of flat groups up to six dimensions and a discussion of all possible lattices are presented.

The Horndeski action is the most general one involving a metric and a scalar field that leads to second-order field equations in four dimensions. Being the natural extension of the well-known scalar-tensor theories, its structure and properties are worth analyzing along the experience accumulated in the latter context. Here, we argue that disformal transformations play, for the Horndeski theory, a similar role to that of conformal transformations for scalar-tensor theories a là Brans–Dicke. We identify the most general transformation preserving second-order field equations and discuss the issue of viable frames for this kind of theory, in particular, the possibility to cast the action in the so-called Einstein frame. Interestingly, we find that only for a subset of the Horndeski Lagrangian such a frame exists. Finally, we investigate the transformation properties of such frames under field redefinitions and frame transformations and their reciprocal relationship.

A novel idea—that the cosmic acceleration can be understood from the perspective that spacetime dynamics is an emergent phenomenon—was proposed by T. Padmanabhan. The Friedmann equations of a Friedmann-Robertson-Walker universe can be derived from different gravity theories with different modifications of Padmanabhan’s proposal. In this paper, a unified formula is proposed, in which those modifications can be treated as special cases when the formula is applied to different universe radii. Furthermore, the dynamic equations of a Friedmann-Robertson-Walker universe in the $f(R)$ theory and deformed Hořava-Lifshitz theory are investigated. The results show the validity of our proposed formula.

We prove the existence of a unique family of nonoscillatory (purely imaginary) polar quasinormal resonances of rapidly-rotating Kerr black holes. These purely imaginary resonances can be expressed in the compact form: ${\omega }_n=-i2\pi T_{\mathrm{BH}}(l+1+n)$, where $T_{\mathrm{BH}}$ is the black-hole temperature, $l$ is the spheroidal harmonic index of the mode, and $n=0,1,2,\dots$ is the resonance parameter. It is shown that our analytical results for the black-hole resonance spectrum agree with new numerical data that recently appeared in the literature.

The inclusion of Dirac fermions in Einstein-Cartan gravity leads to a four-fermion interaction mediated by nonpropagating torsion, which can allow for the formation of a Bardeen-Cooper-Schrieffer condensate. By considering a simplified model in $2+1$ spacetime dimensions, we show that even without an excess of fermions over antifermions, the nonthermal distribution arising from preheating after inflation can give rise to a fermion condensate generated by torsion. We derive the effective Lagrangian for the spacetime-dependent pair field describing the condensate in the extreme cases of nonrelativistic and massless fermions, and show that it satisfies the Gross-Pitaevski equation for a gapless, propagating mode.

We consider different methods to probe the chameleon scalar field with slow neutrons. Chameleons modify the potential of bouncing neutrons over a flat mirror in the terrestrial gravitational field. This induces a shift in the energy levels of the neutrons which could be detected in current experiments like GRANIT. Chameleons between parallel plates have a field profile which is bubblelike and which would modify the phase of neutrons in interferometric experiments. We show that this new method of detection is competitive with the bouncing neutron one, hopefully providing an efficient probe of chameleons when strongly coupled to matter.

The effect of transverse gluons on the chiral symmetry patterns of excited mesons is studied in a Coulomb gauge QCD model. The linear rising static quark-antiquark potential and the transverse gluon propagator known from lattice studies are input into the model. The nonperturbative quark propagator, which enters the meson bound state equations, is derived from the Dyson-Schwinger equations and a complete set of mesons for general spin quantum number is presented. From analyzing the bound state equations for large spins it is demonstrated that chiral and axial symmetry are restored. In this limit a complete degeneracy of all multiplets with given spin is observed. The effect of the transverse gluon interaction is shown to vanish rapidly as the spin quantum number is increased. For vanishing dynamical quark mass the expected meson degeneracies are recovered.

We investigate the LHC and Higgs factory prospects for measuring the $CP$ phase in the Higgs-$\tau \mathrm{\text{−}}\tau$ coupling. Currently this phase can be anywhere between 0° ($CP$ even) and 90° ($CP$ odd). A new, ideal observable is identified from an analytic calculation for the ${\tau }^{\pm }\to {\rho }^{\pm }\nu \to {\pi }^{\pm }{\pi }^0\nu$ channel. It is demonstrated to have promising sensitivity at the LHC and superior sensitivity at the ILC compared to previous proposals. Our observable requires the reconstruction of the internal substructure of decaying taus but does not rely on measuring the impact parameter of tau decays. It is the first proposal for such a measurement at the LHC. For the 14 TeV LHC, we estimate that about $1{\mathrm{ab}}^{-1}$ data can discriminate $CP$ even versus $CP$ odd at the $5\sigma$ level. With $3{\mathrm{ab}}^{-1}$, the $CP$ phase should be measurable to an accuracy of $\sim 11°$. At an $e^{+}{e}^{-}$ Higgs factory, we project that a 250 GeV run with $1{\mathrm{ab}}^{-1}$ luminosity can measure the phase to $\sim 4.4°$ accuracy.

We evaluate the thermodynamic quantities of Yang-Mills theory using the Gribov quantization, which deals with nonperturbative resummation. The magnetic scale is automatically incorporated into the framework and we find it efficient to stabilize the perturbative expansion of the free energy. In the temperature range $T=T_c\sim 2T_c$ the major uncertainty in our results comes from the nonperturbative running coupling that is adopted from the lattice simulation, while the convergence above $2T_c$ is impressively robust. We also present the corresponding interaction measure (i.e., trace anomaly) up to close to $T_c$.

We present a lattice QCD calculation of the ground-state energy shifts of various baryons in a medium of pions or kaons at a single value of the quark mass corresponding to a pion mass of $m_{\pi }\sim 390\mathrm{MeV}$ and a kaon mass of $m_K\sim 540\mathrm{MeV}$, and in a spatial volume $V\sim (4\mathrm{fm}{)}^3$. All systems are created using a canonical formalism in which quark propagators are contracted into correlation functions of fixed isospin/kaon density. We study four different systems, ${\Sigma }^{+}({\pi }^{+}{)}^n$, ${\Xi }^0({\pi }^{+}{)}^n$, $p(K^{+}{)}^n$, and $n(K^{+}{)}^n$, for up to $n=11$ mesons. From the ground-state energy shifts we extract two- and three-body scattering parameters, as well as linear combinations of low-energy constants appearing in tree-level chiral perturbation theory.

We are computing the modifications for the scalar and pseudoscalar meson masses and mixing angles due to the proper accounting of fermionic vacuum fluctuation in the framework of the generalized $2+1$ flavor quark meson model and the Polyakov loop augmented quark meson model (PQM). The renormalized contribution of the divergent fermionic vacuum fluctuation at one loop level makes these models effective QCD-like models. It has been explicitly shown that analytical expressions for the model parameters, meson masses, and mixing angles do not depend on any arbitrary renormalization scale. We have investigated how the incorporation of fermionic vacuum fluctuation in quark meson and PQM models qualitatively and quantitatively affects the convergence in the masses of the chiral partners in pseudoscalar $(\pi ,\eta ,{\eta }^{\prime },K)$ and scalar $(\sigma ,a_0,f_0,\kappa )$ meson nonets as the temperature is varied on the reduced temperature scale. Comparison of present results in the quark meson model with vacuum term and the PQM model with vacuum term with the already existing calculations in the bare $2+1$ quark meson and PQM models shows that the restoration of chiral symmetry becomes smoother due to the influence of the fermionic vacuum term. We find that the melting of the strange condensate registers a significant increase in the presence of the fermionic vacuum term and its highest melting is found in the PQM model with vacuum term. The role of the $U_A(1)$ anomaly in determining the isoscalar masses and mixing angles for the pseudoscalar ($\eta$ and ${\eta }^{\prime }$) and scalar ($\sigma$ and $f_0$) meson complex has also been significantly modified due to the fermionic vacuum correction. In its influence, the interplay of chiral symmetry restoration and the setting up of the $U_A(1)$ restoration trends have also been shown to be significantly modified.

We evaluate the most important tree-level contributions connected with the $b\to u\overline{u}d\gamma$ transition to the inclusive radiative decay $\overline{B}\to X_d\gamma$ using fragmentation functions. In this framework the singularities arising from collinear photon emission from the light quarks ($u$, $\overline{u}$, and $d$) can be absorbed into the (bare) quark-to-photon fragmentation function. We use as input the fragmentation function extracted by the ALEPH group from the two-jet cross section measured at the large electron positron (LEP) collider, where one of the jets is required to contain a photon. To get the quark-to-photon fragmentation function at the fragmentation scale ${\mu }_F\sim m_b$, we use the evolution equation, which we solve numerically. We then calculate the (integrated) photon energy spectrum for $b\to u\overline{u}d\gamma$ related to the operators $P_{1,2}^u$. For comparison, we also give the corresponding results when using nonzero (constituent) masses for the light quarks.

The Pontecorvo-Maki-Nakawaga-Sakata matrix displays an obvious symmetry but not exact. There are several textures proposed in the literature which possess various symmetry patterns and seem to originate from different physics scenarios at high energy scales. To be consistent with the experimental measurement, however, the symmetry must be broken. Following the schemes given in the literature, we modify the matrices (ten in total) to gain the real Pontecorvo-Maki-Nakawaga-Sakata matrix by perturbative rotations. The results may be useful for future model builders.

The first observation of the ${\overline{B}}^0\to J/\psi K^{+}{K}^{-}$ decay is presented with a data sample corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$ of $pp$ collisions at a center-of-mass energy of 7 TeV collected with the LHCb detector. The branching fraction is measured to be $\mathcal{B}({\overline{B}}^0\to J/\psi K^{+}{K}^{-})=(2.53\pm 0.31\pm 0.19)\times {10}^{-6}$, where the first uncertainty is statistical and the second is systematic. An amplitude analysis of the final state in the ${\overline{B}}^0\to J/\psi K^{+}{K}^{-}$ decay is performed to separate resonant and nonresonant contributions in the $K^{+}{K}^{-}$ spectrum. Evidence of the $a_0(980)$ resonance is reported with statistical significance of 3.9 standard deviations. The corresponding product branching fraction is measured to be $\mathcal{B}({\overline{B}}^0\to J/\psi a_0(980),a_0(980)\to K^{+}{K}^{-})=(4.70\pm 3.31\pm 0.72)\times {10}^{-7}$, yielding an upper limit of $\mathcal{B}({\overline{B}}^0\to J/\psi a_0(980),a_0(980)\to K^{+}{K}^{-})<9.0\times {10}^{-7}$ at 90% confidence level. No evidence of the resonant decay ${\overline{B}}^0\to J/\psi \varphi$ is found, and an upper limit on its branching fraction is set to be $\mathcal{B}({\overline{B}}^0\to J/\psi \varphi )<1.9\times {10}^{-7}$ at 90% confidence level.

The axial magnetic field, which couples to left- and right-handed fermions with opposite signs, may generate an equilibrium dissipationless energy flow of fermions in the direction of the field even in the presence of interactions. We report on numerical observation of this axial magnetic effect in quenched $SU(2)$ lattice gauge theory. We find that in the deconfinement (plasma) phase the energy flow grows linearly with the increase of the strength of the axial magnetic field. In the confinement (hadron) phase the axial magnetic effect is absent. Our study indirectly confirms the existence of the chiral vortical effect since both these effects have the same physical origin related to the presence of the gravitational anomaly.