The renormalization group procedure for effective particles in the front form of Hamiltonian dynamics is applied to an elementary quantum field theory for two species of particles mixed through a masslike interaction term. The model interaction generates only finite terms and the procedure yields a whole family of equivalent effective theories. The exact solution for the family is found without involvement of the vacuum state in the dynamics. A physical spectrum is obtained at the end of the procedure in the form of free particles with definite masses. Since the procedure is designed in general terms, it could be used for the purpose of constructing effective dynamics also in other theories than the elementary model.

We consider $3+1$-dimensional fluids with $U(1{)}^3$ anomalies. We use Ward identities to constrain low-momentum Euclidean correlation functions and obtain differential equations that relate two and three-point functions. The solution to those equations yields, among other things, the chiral magnetic conductivity. We then compute zero-frequency functions in hydrodynamics and show that the consistency of the hydrodynamic theory also fixes the anomaly-induced conductivities.

We show, using strong subadditivity and Lorentz covariance, that in three-dimensional space-time the entanglement entropy of a circle is a concave function. This implies the decrease of the coefficient of the area term and the increase of the constant term in the entropy between the ultraviolet and infrared fixed points. This is in accordance with recent holographic $c$ theorems and with conjectures about the renormalization group flow of the partition function of a three sphere ($F$ theorem). The irreversibility of the renormalization group flow in three dimensions would follow from the argument provided there is an intrinsic definition for the constant term in the entropy at fixed points. We discuss the difficulties in generalizing this result for spheres in higher dimensions.

We reexamine the classic problem of the renormalization of zero-point quantum fluctuations in a Friedmann-Robertson-Walker background. We discuss a number of issues that arise when regularizing the theory with a momentum-space cutoff, and show explicitly how introducing noncovariant counterterms allows to obtain covariant results for the renormalized vacuum energy-momentum tensor. We clarify some confusion in the literature concerning the equation of state of vacuum fluctuations. Further, we point out that the general structure of the effective action becomes richer if the theory contains a scalar field $\varphi$ with mass $m$ smaller than the Hubble parameter $H(t)$. Such an ultralight particle cannot be integrated out completely to get the effective action. Apart from the volume term and the Einstein-Hilbert term, that are reabsorbed into renormalizations of the cosmological constant and Newton’s constant, the effective action in general also has a term proportional to $F(\varphi )R$, for some function $F(\varphi )$. As a result, vacuum fluctuations of ultralight scalar fields naturally lead to models where the dark energy density has the form ${\rho }_{\mathrm{DE}}(t)={\rho }_X(t)+{\rho }_Z(t)$, where ${\rho }_X$ is the component that accelerates the Hubble expansion at late times and ${\rho }_Z(t)$ is an extra contribution proportional to $H^2(t)$. We perform a detailed comparison of such models with CMB, SNIa and BAO data.

In this paper, we consider the relation between the super-renormalizable theories of quantum gravity studied by Biswas, Gerwick, Koivisto, and Mazumdar [Phys. Rev. Lett. 108, 031101 (2012)] and Modesto [arXiv:1107.2403; arXiv:1202.0008] and an underlying noncommutativity of space-time. For one particular super-renormalizable theory, we show that at the linear level (quadratic in the Lagrangian) the propagator of the theory is the same one we obtain starting from a theory of gravity endowed with $\theta$-Poincaré quantum groups of symmetry. Such a theory is over the so-called $\theta$-Minkowski noncommutative space-time. We shed new light on this link and show that, among the theories considered in these references, there exists only one nonlocal and Lorentz invariant super-renormalizable theory of quantum gravity that can be described in terms of a quantum-group symmetry structure. We also emphasize contact with preexistent works in the literature and discuss preservation of the equivalence principle in our framework.

We study the strong gravitational lensing in the background of a rotating non-Kerr compact object with a deformed parameter $ϵ$ and an unbound rotation parameter $a$. We find that the marginally circular stable orbit radius and the deflection angle depend sharply on the parameters $ϵ$ and $a$. For the case in which the black hole is more prolate than a Kerr black hole, the marginally circular photon orbit exists only in the regime $ϵ\le {ϵ}_{\max }$ for a prograde photon. The upper limit ${ϵ}_{\max }$ is a function of the rotation parameter $a$. As $ϵ>{ϵ}_{\max }$, the deflection angle of the light ray very close to the naked singularity is a positive finite value, which is different from that in the rotating naked singularity described by Janis-Newman-Winicour metric. For the oblate black hole and the retrograde photon, there does not exist such a threshold value. Modeling the supermassive central object of the Galaxy as a rotating non-Kerr compact object, we estimated the numerical values of the coefficients and observables for gravitational lensing in the strong field limit.

The bispectrum of the cosmic microwave background generated by a correlation between a time-dependent gravitational potential and the weak gravitational lensing effect provides a direct measurement of the influence of dark energy on cosmic microwave background. This bispectrum is also known to yield the most important contamination of the so-called “localform” primordial bispectrum, which can be used to rule out all single-field inflation models. In this paper, we reexamine the effect of nonlinear matter clustering on this bispectrum. We compare three different approaches: the 3rd-order perturbation theory, and two empirical fitting formulae available in the literature, finding that detailed modeling of nonlinearity appears to be not very important, as most of the signal to noise comes from the squeezed triangle, for which the correlation in the linear regime dominates. The expected signal-to-noise ratio for an experiment dominated by the cosmic variance up to $l_{\max }=1500$ is about 5, which is much smaller than the previous estimates including nonlinearity, but agrees with the estimates based on the linear calculation. We find that the difference between the linear and nonlinear predictions is undetectable, and does not alter the contamination of the localform primordial non-Gaussianity.

The gravitational wave signal from a binary neutron star inspiral contains information on the nuclear equation of state. This information is contained in a combination of the tidal polarizability parameters of the two neutron stars and is clearest in the late inspiral, just before merger. We use the recently defined tidal extension of the effective one-body formalism to construct a controlled analytical description of the frequency-domain phasing of neutron star inspirals up to merger. Exploiting this analytical description we find that the tidal polarizability parameters of neutron stars can be measured by the advanced LIGO-Virgo detector network from gravitational wave signals having a reasonable signal-to-noise ratio of $\rho =16$. This measurability result seems to hold for all the nuclear equations of state leading to a maximum mass larger than $1.97M_{\odot }$. We also propose a promising new way of extracting information on the nuclear equation of state from a coherent analysis of an ensemble of gravitational wave observations of separate binary merger events.

We investigate the effect of modified gravity with screening mechanisms, such as the chameleon or symmetron models, upon the structure of main sequence stars. We find that unscreened stars can be significantly more luminous and ephemeral than their screened doppelgangers. By embedding these stars into dwarf galaxies, which can be unscreened for values of the parameters not yet ruled out observationally, we show that the cumulative effect of their increased luminosity can enhance the total galactic luminosity. We estimate this enhancement and find that it can be considerable given model parameters that are still under experimental scrutiny. By looking for systematic offsets between screened dwarf galaxies in clusters and unscreened galaxies in voids, these effects could form the basis of an independent observational test that can potentially lower the current experimental bounds on the model independent parameters of these theories by an order of magnitude or more.

We investigate the constraints that can be placed on the cosmic string tension by using the current pulsar timing array (PTA) limits on the gravitational wave background. We have developed a code to compute the spectrum of gravitational waves (GWs) based on the widely accepted one-scale model. In its simplest form the one-scale model for cosmic strings allows one to vary: (i) the string tension, $G\mu /c^2$; (ii) the size of cosmic string loops relative to the horizon at birth, $\alpha$; (iii) the spectral index of the emission spectrum, $q$; (iv) the cutoff in the emission spectrum, $n_{*}$; and (v) the intercommutation probability, $p$. The amplitude and slope of the spectrum in the nHz frequency range is very sensitive to these unknown parameters. We have also investigated the impact of more complicated scenarios with multiple initial loop sizes $\alpha$, in particular, the $2\mathrm{\text{−}}\alpha$ models proposed in the literature and a log-normal distribution for $\alpha$. We have computed the constraint on $G\mu /c^2$ due to the limit on a stochastic background of GWs imposed by the European Pulsar Timing Array. Taking into account all the possible uncertainties in the parameters we find a conservative upper limit of $G\mu /c^2<5.3\times {10}^{-7}$ which typically occurs when the loop production scale is close to the gravitational backreaction scale, $\alpha \approx \Gamma G\mu /c^2$. Stronger limits are possible for specific values of the parameters which typically correspond to the extremal cases $\alpha \ll \Gamma G\mu /c^2$ and $\alpha \gg \Gamma G\mu /c^2$. This limit is less stringent than the previously published limits which are based on cusp emission, an approach which does not necessarily model all the possible uncertainties. We discuss the prospects for lowering this limit by 2 orders of magnitude, or even a detection of the GW background, in the very near future in the context of the Large European Array for Pulsars and the Square Kilometre Array.

We revisit the issue of color neutrality in effective model descriptions of dense quark matter based on global color symmetry. While the equilibrium thermodynamics of such models is now well understood, we examine the collective modes, focusing on the fluctuations of the order parameter. We point out that the constraint of color neutrality must be carefully generalized in order to obtain physically consistent and well-defined results. Particularly important is that the collective modes associated with order parameter fluctuations couple to charge density fluctuations in the neutral medium. We start by proving explicitly that, in contrast to claims made previously in literature, Nambu-Goldstone bosons of spontaneously broken global color symmetry remain exactly massless even after imposing the color neutrality constraint. As the next step, we make the argument general by using effective field theory. We then employ the high-density approximation to calculate the couplings in the effective Lagrangian and thus the Nambu-Goldstone boson dispersion relations.

We derive the relation between the scattering phase shift and the two-particle energy in the finite box, which is relevant for extracting the strong phase shifts in lattice QCD. We consider elastic scattering of two particles with different mass and with nonzero total momentum in the lattice frame. This is a generalization of the Lüscher formula, which considers zero total momentum, and a generalization of Rummukainen-Gottlieb’s formula, which considers degenerate particles with nonzero total momentum. We focus on the most relevant total momenta in practice, i.e. $\mathbf{P}=(2\pi /L)e_z$ and $\mathbf{P}=(2\pi /L)(e_x+e_y)$, including their multiples and permutations. We find that the $P$-wave phase shift can be reliably extracted from the two-particle energy if the phase shifts for $l\ge 2$ can be neglected, and we present the corresponding relations. The reliable extraction of the $S$-wave phase shift is much more challenging since ${\delta }_{l=0}$ is always accompanied by ${\delta }_{l=1}$ in the phase shift relations, and we propose strategies for estimating ${\delta }_{l=0}$. We also propose the quark-antiquark and meson-meson interpolators that transform according the considered irreducible representations.

The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to $2.05{\mathrm{fb}}^{-1}$ of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of $R$-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600–900 GeV are excluded, depending on the model considered.

We obtain the Matrix model equations in the background of the maximally supersymmetric $pp$-wave solution of the 11D supergravity and discuss its relation with the Berenstein-Maldacena-Nastase model.

In AdS/CFT, the holographic Weyl anomaly computation relates the $a$-anomaly coefficient to the properties of the bulk action at the UV fixed point. This universal behavior suggests the possibility of a holographic $c$-theorem for the $a$ anomaly under flows to the IR. We prove such a $c$-theorem for higher-curvature Lovelock gravity, where the bulk equations of motion remain second order. We also explore $f(R)$ gravity as a toy model where higher derivatives cannot be avoided. In this case, monotonicity of the flow requires an additional condition related to the higher derivative nature of the theory. This is in contrast to the case of $f(R)$ black hole entropy, where the second law follows from application of the full Einstein equations and the null energy condition.

There has been some recent interest in the study of non-Abelian Bogomolny-Prasad-Sommerfield (BPS) monopoles in the limit of large magnetic charge. Most investigations have used a magnetic bag approximation, in which spherical symmetry is assumed within an Abelian description. In particular, this approach has been used to suggest the existence of two types of magnetic bags, with differing distributions of the zeros of the Higgs field, together with multilayer structures, containing several magnetic bags. This paper is concerned with the analogous situation of Abelian BPS vortices in the hyperbolic plane, in the limit of large magnetic flux. This system has the advantage that explicit exact solutions can be obtained and compared with a magnetic bag approximation. Exact BPS vortex solutions are presented that are analogous to the two types of magnetic bags predicted for BPS monopoles and it is shown that these structures can be combined to produce exact multilayer solutions.

In this work, we derive a recently proposed Abelian model to describe correlated monopoles, center vortices, and dual fields in three-dimensional $SU(2)$ Yang-Mills theory. Following recent polymer techniques, special care is taken to obtain the end-to-end probability for a single interacting center vortex, which constitutes a key ingredient to represent the ensemble integration.

We study gravitationally bound, spherically symmetric equilibrium configurations consisting of ordinary (neutron-star) matter and of a phantom/ghost scalar field which provides the nontrivial topology in the system. For such mixed configurations, we show the existence of static, regular, asymptotically flat general relativistic solutions. Based on the energy approach, we discuss the stability as a function of the core density of the neutron matter for various sizes of the wormhole throat.

We compute the black hole radiation spectrum in the presence of high-frequency dispersion in a large set of situations. In all cases, the spectrum diverges like the inverse of the Killing frequency. When studying the low-frequency spectrum, we find only two regimes: an adiabatic one where the corrections with respect to the standard temperature are small, and an abrupt one regulated by dispersion, in which the near-horizon metric can be replaced by step functions. The transition from one regime to the other is governed by a single parameter which also governs the net redshift undergone by dispersive modes. These results can be used to characterize the quasiparticles spectrum of recent and future experiments aiming to detect the analogue Hawking radiation. They also apply to theories of quantum gravity which violate Lorentz invariance.