Searches for rare processes such as $\mu \to e\gamma$ put stringent limits on lepton flavor violation expected in many beyond-the-Standard-Model physics scenarios. This usually precludes the observation of flavor violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a $Z^{\prime }$ portal but which can only decay via small flavor violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small $\mu \to e\gamma$ rates.

We employ methods of gauge/string duality to analyze the nonrelativistic Brownian motion and the concomitant Langevin equation of a heavy quark in a strongly coupled, thermal, anisotropic Yang-Mills plasma in the low anisotropy limit. We consider fluctuations both along and perpendicular to the direction of anisotropy and study the effects of anisotropy on the drag coefficient, the diffusion constant, and the Langevin coefficient for both the directions. We also verify the fluctuation-dissipation theorem for Brownian motion in an anisotropic medium.

A simple extension of the minimal left-right symmetric supersymmetric grand unified theory model is constructed by adding two pairs of superfields. This naturally violates the partial Yukawa unification predicted by the minimal model. After including supergravity corrections, we find that this extended model naturally supports hilltop $F$-term hybrid inflation along its trivial inflationary path with only a very mild tuning of the initial conditions. With a convenient choice of signs of the terms in the Kähler potential, we can reconcile the inflationary scale with the supersymmetric grand unified theory scale. All the current data on the inflationary observables are readily reproduced. Inflation is followed by nonthermal leptogenesis via the decay of the right-handed neutrinos emerging from the decay of the inflaton, and any possible washout of the lepton asymmetry is avoided thanks to the violation of partial Yukawa unification. The extra superfields also assist us in reducing the reheat temperature so as to satisfy the gravitino constraint. The observed baryon asymmetry of the universe is naturally reproduced consistently with the neutrino oscillation parameters.

We consider the standard model extended by a hidden sector $\mathrm{U}{(1)}_X$ symmetry that is spontaneously broken at the TeV scale by the vacuum expectation value of an additional scalar field. We study “dark string” solutions in this model and their properties due to the Higgs portal and gauge kinetic mixing operators. We find that dark strings effectively interact with Higgs and $Z$ bosons by linear couplings, and with leptons and baryons via Aharonov-Bohm couplings, thus possibly leading to new cosmological constraints on dark matter models with spontaneously broken extra U(1) symmetry factors.

The determination of $|V_{us}|$ from kaon semileptonic decays requires the value of the form factor $f_{+}(q^2=0)$, which can be calculated precisely on the lattice. We provide the one-loop partially quenched staggered chiral perturbation theory expressions that may be employed to analyze staggered simulations of $f_{+}(q^2)$ with three light flavors. We consider both the case of a mixed action, where the valence and sea sectors have different staggered actions, and the standard case, where these actions are the same. The momentum transfer $q^2$ of the form factor is allowed to have an arbitrary value. We give results for the generic situation where the $u$, $d$, and $s$ quark masses are all different, $N_f=1+1+1$, and for the isospin limit, $N_f=2+1$. The expression we obtain for $f_{+}(q^2)$ is independent of the mass of the (valence) spectator quark. In the limit of vanishing lattice spacing, our results reduce to the one-loop continuum partially quenched expression for $f_{+}(q^2)$, which has not previously been reported in the literature for the $N_f=1+1+1$ case. Our expressions have already been used in staggered lattice analyses of $f_{+}(0)$ and should prove useful in future calculations as well.

Using finite temperature SU(3) lattice gauge theory in the fixed scale approach we analyze center properties of the local Polyakov loop $L(x)$. We construct spatial clusters of points $x$ where the phase of $L(x)$ is near the same center element and study their properties as a function of temperature. We find that below the deconfinement transition the clusters form objects with a fractal dimension $D<3$. As the temperature is increased, the largest cluster starts to percolate and its dimensionality approaches $D=3$. The fractal structure of the clusters in the transition region may have implications regarding both the small shear viscosity and the large opacity of the quark gluon plasma observed in heavy-ion collision experiments.

In the so-called unified dark fluid models, the dark sector gets simplified because dark matter and dark energy are replaced by a single fluid that behaves as the former at early times and as the latter at late times. In this short paper we analyze this class of models from the thermodynamic viewpoint. While the second law of thermodynamics is satisfied, the first two derivatives of the entropies of the apparent horizon and of the energy components suffer such a sharp oscillation that doubts are raised about the soundness of this class of models.

We demonstrate the generation of the three-dimensional Chern-Simons–like Lorentz-breaking “mixed” quadratic action via an appropriate Lorentz-breaking coupling of vector and scalar fields to the spinor field and study some features of the scalar QED with such a term. We show that the same term emerges through a nonperturbative method, namely the Julia-Toulouse approach of condensation of charges and defects.

We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field, using holography. The physical quantities related to the chiral symmetry breaking ($m,B_c$) distinguish between the effects of the anisotropy and magnetic field on the plasma. Anisotropy affects the system similar to the temperature and for its larger values heavier quarks can live in the QGP without getting condensed. Raising the anisotropy in the system will also increase the value of the critical magnetic field, $B_c$, at which the spontaneous chiral symmetry breaking happens. Both of these growths are even more when the magnetic field is applied perpendicular to the anisotropy direction. Such behavior persists in the high temperature limit where the temperature is kept fixed. However, when the entropy density is held fixed, as one increases the anisotropy, lighter mesons melt when the magnetic field is applied along the anisotropy direction, in contrast to when the magnetic field is perpendicular to the anisotropy direction.

In quantum metrology quantum properties such as squeezing and entanglement are exploited in the design of a new generation of clocks, sensors and other measurement devices that can outperform their classical counterparts. Applications of great technological relevance lie in the precise measurement of parameters which play a central role in relativity, such as proper accelerations, relative distances, time and gravitational field strengths. In this paper we generalize recently introduced techniques to estimate physical quantities within quantum field theory in flat and curved space-time. We consider a bosonic quantum field that undergoes a generic transformation, which encodes the parameter to be estimated. We present analytical formulas for optimal precision bounds on the estimation of small parameters in terms of Bogoliubov coefficients for single-mode and two-mode Gaussian channels.

We obtain the Schwarzschild solution from thermodynamic considerations using the assumptions of a quasilocal mass form (the Misner-Sharp mass) and geometric surface gravity in a spherically symmetric space-time. The deduction is extended to other cases such as the de Sitter, anti–de Sitter, Reissner-Nordström, and higher-dimensional space-times. This paper demonstrates the simple hypotheses to obtain these known spherically symmetric solutions via thermodynamics, where essentially the Misner-Sharp mass is the mass for an adiabatic system.

We study dynamics of Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime based on the ghost-free bigravity theory. Assuming the coupling parameters guaranteeing the existence of de Sitter space as well as Minkowski spacetime, we find two stable attractors for spacetime with “twin” dust matter fields: One is de Sitter accelerating universe and the other is matter dominated universe. Although a considerable number of initial data leads to de Sitter universe, we also find matter dominated universe or spacetime with a future singularity for some initial data. The cosmic no-hair conjecture does not exactly hold, but the accelerating expansion can be found naturally. The $\mathrm{\Lambda }$-CDM model is obtained as an attractor. We also show that the dark matter component in the Friedmann equation, which originates from another twin matter, can be about 5 times larger than the baryonic matter, by choosing the appropriate coupling constants.

We prove a Jebsen-Birkhoff-like theorem for $f(R)$ theories of gravity in order to find the necessary conditions required for the existence of the Schwarzschild solution in these theories and demonstrate that the rigidity of such solutions of $f(R)$ gravity is valid even in the perturbed scenario.

It has been found in previous studies that, for the Supernova Legacy Survey three-year (SNLS3) data, there is strong evidence for the redshift evolution of color-luminosity parameter $\beta$. In this paper, using the three simplest dark energy models, i.e., the $\mathrm{\Lambda }$-cold-dark-matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, the $w\mathrm{CDM}$ model, and the Chevallier-Polarski-Linder model, we further explore the evolution of $\beta$ and its effects on parameter estimation. In addition to the SNLS3 data, we also take into account the Planck distance priors data of the cosmic microwave background (CMB), as well as the latest galaxy clustering (GC) data extracted from SDSS DR7 and BOSS. We find that, for all the models, adding a parameter of $\beta$ can reduce ${\chi }_{\min }^2$ by $\sim 36$, indicating that ${\beta }_1=0$ is ruled out at $6\sigma$ confidence levels. In other words, $\beta$ deviates from a constant at 6$\sigma$ confidence levels. This conclusion is insensitive to the dark energy models considered, showing the importance of considering the evolution of $\beta$ in the cosmology fits. Furthermore, it is found that varying $\beta$ can significantly change the fitting results of various cosmological parameters: using the SNLS3 data alone, varying $\beta$ yields a larger ${\mathrm{\Omega }}_m$ for the $\mathrm{\Lambda }\mathrm{CDM}$ model; using the $\mathrm{SNLS}3+\mathrm{CMB}+\mathrm{GC}$ data, varying $\beta$ yields a larger ${\mathrm{\Omega }}_m$ and a smaller $h$ for all the models. Moreover, we find that these results are much closer to those given by the $\mathrm{CMB}+\mathrm{GC}$ data compared to the cases of treating $\beta$ as a constant. This indicates that considering the evolution of $\beta$ is very helpful for reducing the tension between supernova and other cosmological observations.

We propose a mechanism by which the inflaton can generate baryogenesis, by taking the inflaton to be a complex scalar field with a weakly broken global symmetry, and present a new version of the Affleck–Dine mechanism. The smallness of the breaking is motivated both by technical naturalness and a requirement for inflation. We study inflation driven by a quadratic potential for simplicity and discuss generalizations to other potentials. We compute the inflationary dynamics and find that a conserved particle number is obtained toward the end of inflation. We then explain in detail the later decay to baryons. We present two promising embeddings in particle physics. (i) The first is using high-dimension operators for a gauge singlet; we find this leads to the observed asymmetry for decay controlled by the $\sim \text{grand}$ unified theory scale, and this is precisely the regime where the effective field theory applies. (ii) The second is using a colored inflaton, which requires small couplings. We also point out two observational consequences: a possible large-scale dipole in the baryon density and a striking prediction of isocurvature fluctuations for which the amplitude is found to be just below current limits and potentially detectable in future data.

Most of the mass of ordinary matter has its origin from quantum chromodynamics (QCD). A similar strong dynamics, dark QCD, could exist to explain the mass origin of dark matter. Using infrared fixed points of the two gauge couplings, we provide a dynamical mechanism that relates the dark QCD confinement scale to our QCD scale, and hence provides an explanation for comparable dark baryon and proton masses. Together with a mechanism that generates equal amounts of dark baryon and ordinary baryon asymmetries in the early Universe, the similarity of dark matter and ordinary matter energy densities can be naturally explained. For a large class of gauge group representations, the particles charged under both QCD and dark QCD, necessary ingredients for generating the infrared fixed points, are found to have masses at 1–2 TeV, which sets the scale for dark matter direct detection and novel collider signatures involving visible and dark jets.

We study the imprint of a coupling of scalar dark energy to a photon on the cosmic microwave background polarization. Both the time-evolving field value and the perturbation of the scalar induce $B$-mode polarization. For a wide range of scalar dark energy models allowed by current observational data, we conclude that future cosmic microwave background data will find either a cosmic parity violation in a temperature-polarization correlation due to the field value, or perturbation-induced $B$-mode polarization that is indistinguishable from that generated by primordial gravitational waves.

We study the superradiant scattering of gravitational waves by a nearly extremal black hole (dimensionless spin $a=0.99$) by numerically solving the full Einstein field equations, thus including backreaction effects. This allows us to study the dynamics of the black hole as it loses energy and angular momentum during the scattering process. To explore the nonlinear phase of the interaction, we consider gravitational wave packets with initial energies up to 10% of the mass of the black hole. We find that as the incident wave energy increases, the amplification of the scattered waves, as well as the energy extraction efficiency from the black hole, is reduced. During the interaction the apparent horizon geometry undergoes sizable nonaxisymmetric oscillations. The largest amplitude excitations occur when the peak frequency of the incident wave packet is above where superradiance occurs, but close to the dominant quasinormal mode frequency of the black hole.

In light of recent and probably incoming observations of very high energy astroparticles, such as those reported by the IceCube collaboration, we readdress the energy loss mechanism by Lorentz violating particles. We analytically show that Cohen–Glashow’s formula for energy loss is connected with a Poisson distribution for the number of decays, for which the large fluctuations prevent placing bounds on Lorentz invariance violations. However, this model ignores the sharp change in the decay width after each process. We propose replacing Poisson statistics with a new distribution that takes this into account. We study the average final energy and its fluctuations according to the new statistics, contrasting it with Cohen–Glashow’s result, and discussing the reliability of energy loss mechanisms to constrain violations of Lorentz invariance.

We describe an effective theory of interaction between pairs of dark matter particles and pairs of photons. Such an interaction could accommodate $\chi \overline{\chi }\to \gamma \gamma$ processes, which might be the cause of the observed feature in the FermiLAT spectrum, as well as ${\gamma }^{*}/Z\to \gamma \chi \overline{\chi }$ processes, which would predict excesses at the LHC in the $\gamma +{\cancel{E}}_T$ final state. We reinterpret an ATLAS $\gamma +{\cancel{E}}_T$ analysis and the observed Fermi feature in the parameter space of our new effective theory to assess their consistency.