Prompted by the recent observation of a Higgs-like particle at the CERN Large Hadron Collider, we investigate a quantitative correlation between possible departures of the gauge and Yukawa couplings of this particle from their Standard Model expectations and the scale of unitarity violation in the processes $WW\to WW$ and $t\overline{t}\to WW$.

The odd-parity nucleon spectrum is examined in the light quark-mass regime in $2+1$ flavor lattice QCD. Configurations generated by the PACS-CS Collaboration and made available through the International Lattice Data Grid are used, with the lightest pion mass at 156 MeV. A novel method for tracking the individual energy eigenstates as the quark mass changes is introduced. The success of this approach reveals the flow of the states towards the physical masses. Using the correlation-matrix method, the two lowest-energy states revealed are found to be in accord with the physical spectrum of nature.

It is shown that different pairs of stress-energy and spin tensors of quantum relativistic fields related by a pseudo-gauge transformation, i.e., differing by a divergence, imply different mean values of physical quantities in thermodynamical nonequilibrium situations. Most notably, transport coefficients and the total entropy production rate are affected by the choice of the spin tensor of the relativistic quantum field theory under consideration. Therefore, at least in principle, it should be possible to disprove a fundamental stress-energy tensor and/or to show that a fundamental spin tensor exists by means of a dissipative thermodynamical experiment.

Using a nonperturbative approximation for the partition function of a complex scalar model, which features spontaneous symmetry breaking, we explicitly derive the flattening of the effective potential in the region limited by the minima of the bare potential. This flattening occurs in the limit of infinite volume and is a consequence of the summation over the continuous set of saddle points which dominate the partition function. We also prove the convexity of the effective potential and generalize the Maxwell construction for scalar theories with $O(N)$ symmetry. Finally, we discuss why the flattening of the effective potential cannot occur in the Abelian Higgs theory.

As atoms formed for the first time during primordial recombination, they emitted bound-bound and free-bound radiation leading to spectral distortions to the cosmic microwave background. These distortions might become observable in the future with high-sensitivity spectrometers, and provide a new window into physical conditions in the early universe. The standard multilevel atom method habitually used to compute the recombination spectrum is computationally expensive, impeding a detailed quantitative exploration of the information contained in spectral distortions thus far. In this work it is shown that the emissivity in optically thin allowed transitions can be factored into a computationally expensive but cosmology-independent part and a computationally cheap, cosmology-dependent part. The slow part of the computation consists in pre-computing temperature-dependent effective “conductances,” linearly relating line or continuum intensity to departures from Saha equilibrium of the lowest-order excited states ($2s$ and $2p$), that can be seen as “voltages.” The computation of these departures from equilibrium as a function of redshift is itself very fast, thanks to the effective multilevel atom method introduced in an earlier work. With this factorization, the recurring cost of a single computation of the recombination spectrum is only a fraction of a second on a standard laptop, more than four orders of magnitude shorter than standard computations. The spectrum from helium recombination can be efficiently computed in an identical way, and a fast code computing the full primordial recombination spectrum with this method will be made publicly available soon.

We analytically derive a more accurate formula for the power spectrum of the biased objects with the primordial non-Gaussianity parametrized not only by the nonlinearity parameter $f_{\mathrm{NL}}$, but also by $g_{\mathrm{NL}}$ and ${\tau }_{\mathrm{NL}}$ which characterize the trispectrum of the primordial curvature perturbations. We adopt the integrated perturbation theory which was constructed in Matsubara [Phys. Rev. D 83, 083518 (2011)]. We discuss an inequality between $f_{\mathrm{NL}}$ and ${\tau }_{\mathrm{NL}}$ in the context of the scale-dependent bias, by introducing a stochasticity parameter. We also mention higher order loop corrections in the scale dependency of the bias parameter.

Several authors have previously shown that a Gpc-scale void based on the spherically symmetric Lemaître-Tolman-Bondi (LTB) model can provide a good fit to certain cosmological data, including the SNIa data, but it is only consistent with the observed CMB dipole if we are located very close to the center, in violation of the Copernican principle. In this work we investigate the more general quasispherical Szekeres model, which does not include spherical symmetry, in order to determine whether this option may be less constricting. We find that the observer is still constrained to a small region, but it is not as geometrically “special” as the center of a LTB void. Furthermore, whereas the quadrupole and octupole near the center of a LTB void are necessarily small, certain Szekeres models can include a significant quadrupole while still being consistent with the observed dipole, hinting that Szekeres models may be able to give an explanation for the observed quadrupole/octupole anomalies.

Models that seek to produce a line at $\sim 130\mathrm{GeV}$ as possibly present in the Fermi data face a number of phenomenological hurdles, not the least of which is achieving the high cross section into $\gamma \gamma$ required. A simple explanation is a fermionic dark matter particle that couples to photons through loops of charged messengers. We study the size of the dimension-5 dipole (for a pseudo-Dirac state) and dimension-7 Rayleigh operators in such a model, including all higher order corrections in $1/M_{\mathrm{mess}}$. Such corrections tend to enhance the annihilation rates beyond the naive effective operators. We find that while freeze-out is generally dominated by the dipole, the present-day gamma-ray signatures are dominated by the Rayleigh operator, except at the most strongly coupled points, motivating a hybrid approach. With this, the magnetic inelastic dark matter scenario provides a successful explanation of the lines at only moderately strong coupling. We also consider the pure Majorana weakly interacting massive particle, where both freeze-out and the Fermi lines can be explained, but only at very strong coupling with light ($\sim 200–300\mathrm{GeV}$) messengers. In both cases there is no conflict with nonobservation of continuum photons.

We study chiral symmetry breaking for fundamental charged fermions coupled electromagnetically to photons with the inclusion of a four-fermion contact self-interaction term, characterized by coupling strengths $\alpha$ and $\lambda$, respectively. We employ multiplicatively renormalizable models for the photon dressing function and the electron-photon vertex that minimally ensures mass anomalous dimension ${\gamma }_m=1$. Vacuum polarization screens the interaction strength. Consequently, the pattern of dynamical mass generation for fermions is characterized by a critical number of massless fermion flavors $N_f=N_f^c$ above which chiral symmetry is restored. This effect is in diametrical opposition to the existence of criticality for the minimum interaction strengths, ${\alpha }_c$ and ${\lambda }_c$, necessary to break chiral symmetry dynamically. The presence of virtual fermions dictates the nature of phase transition. Miransky scaling laws for the electromagnetic interaction strength $\alpha$ and the four-fermion coupling $\lambda$, observed for quenched QED, are replaced by a mean field power law behavior corresponding to a second-order phase transition. These results are derived analytically by employing the bifurcation analysis and are later confirmed numerically by solving the original nonlinearized gap equation. A three-dimensional critical surface is drawn in the phase space of $(\alpha ,\lambda ,N_f)$ to clearly depict the interplay of their relative strengths to separate the two phases. We also compute the $\beta$ functions (${\beta }_{\alpha }$ and ${\beta }_{\lambda }$) and observe that ${\alpha }_c$ and ${\lambda }_c$ are their respective ultraviolet fixed points. The power law part of the momentum dependence, describing the mass function, implies ${\gamma }_m=1+s$, which reproduces the quenched limit trivially. We also comment on the continuum limit and the triviality of QED.

The azimuthal $\cos \varphi$ and $\cos 2\varphi$ modulations of the distribution of hadrons produced in unpolarized semi-inclusive deep-inelastic scattering of electrons and positrons off hydrogen and deuterium targets have been measured in the HERMES experiment. For the first time these modulations were determined in a four-dimensional kinematic space for positively and negatively charged pions and kaons separately, as well as for unidentified hadrons. These azimuthal dependences are sensitive to the transverse motion and polarization of the quarks within the nucleon via, e.g., the Cahn, Boer-Mulders and Collins effects.

We consider the correlation function of a circular Wilson loop with two local scalar operators at generic four positions $a_1$, $a_2$ in planar $\mathcal{N}=4$ supersymmetric gauge theory. We show that such a correlator is fixed by conformal invariance up to a function $F(\mathrm{u},\mathrm{v};\lambda )$ of two scalar combinations $\mathrm{u},\mathrm{v}$ of $a_1$, $a_2$ coordinates invariant under the conformal transformations preserving the circle as well as the ’t Hooft coupling $\lambda$. We compute this function at leading orders at weak and strong coupling for some simple choices of local supersymmetric operators. We also check that correlators of an infinite line Wilson loop with local operators are the same as those for the circular loop.

We explore the effect of a magnetic field on the electromagnetic signature in QCD-like plasma by taking the AdS/CFT approach. Concretely, we choose two QCD gravity dual models to do comparative studies: the D4/D6 and D3/D7 models. The magnetic field is simulated by a spatial component of the flavor U(1) gauge field in the bulk side. For both models, we plot the spectral function and photoemission rate for lightlike momenta as well as the ac conductivity. Due to the presence of the magnetic field, the rotational symmetry is partially broken. Therefore, we plot the spectral function and photoemission rate with spatial momentum parallel or perpendicular to the magnetic field, respectively. We find that the magnetic field induces an anisotropic feature in the electromagnetic signature. To be specific, when the emitted photons from the plasma are moving along the magnetic field, the electromagnetic signature is weakened as the magnetic field is increasing; on the contrary, when the produced photons move perpendicular to the magnetic field, the magnetic field has the effect of amplifying the electromagnetic signature. This should have a relationship with the anisotropic feature of the photon signal observed in heavy-ion collision experiments. This anisotropic characteristic can also be observed in the ac conductivity of the holographic plasma. In the infrared regime of the frequency, the magnetic field suppresses the ac conductivity (along the direction perpendicular to the magnetic field) and likely gives a pseudogap structure. However, the ac conductivity along the magnetic field is enhanced due to the presence of the magnetic field.

We formulate a set of consistency conditions appropriate to worldsheet form factors in the massive, integrable but nonrelativistic, light-cone gauge fixed ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ string theory. We then perturbatively verify that these conditions hold, at tree level in the near-plane-wave limit and to one loop in the near-flat (Maldacena-Swanson) limit, for a number of specific cases. We further study the form factors in the weakly coupled dual description, verifying that the relevant conditions naturally hold for the one-loop Heisenberg spin chain. Finally, we note that the near-plane-wave expressions for the form factors, when further expanded in small momentum or, equivalently, large charge density, reproduce the thermodynamic limit of the spin-chain results at leading order.

We study massive $1/2$-spin particles in various external backgrounds, keeping in mind applications to neutrino physics. We are mainly interested in massive Majorana (Weyl) fields. However, massive neutral Dirac particles are also considered. We formulate classical Lagrangian theory of the massive Weyl field in terms of Grassmann-odd two-component spinors. Then, we construct the Hamiltonian formulation of such a theory, which turns out to be a theory with second-class constraints. Using this formulation, we canonically quantize the massive free Weyl field. We derive propagators of the Weyl field and relate them to the propagator of a massive Dirac particle. We also study the massive Weyl particles propagating in the background mater. We find the path integral representation for the propagator of such a field, as well as the corresponding pseudoclassical particle action. The massless limit of the Weyl field interacting with the matter is considered and compared with results of other works. Finally, the path integral representation for the propagator of the neutral massive Dirac particle with an anomalous magnetic moment moving in the background matter and external electromagnetic field, as well as the corresponding pseudoclassical particle action, are constructed.

We construct $d=1$ sigma models of the Wess-Zumino type on the $SU(n|1)/U(n)$ fermionic cosets. Such models can be regarded as a specific supersymmetric generalization (with a target space supersymmetry) of the classical Landau model, when a charged particle possesses only fermionic coordinates. We consider both classical and quantum models, and we prove the unitarity of the quantum model by introducing the metric operator on the Hilbert space of the quantum states, such that all their norms become positive definite. It is remarkable that the quantum $n=2$ model exhibits hidden $SU(2|2)$ symmetry. We also discuss the planar limit of these models. The Hilbert space in the planar $n=2$ case is shown to carry $SU(2|2)$ symmetry which is different from that of the $SU(2|1)/U(1)$ model.

Motivated by recent works, the influences of self-gravitational interaction on the Hawking radiation are studied both for ($3+1$) and ($4+1$) dimensional black holes in $z=4$ Hořava-Lifshitz gravity. It is found that the tunneling entropies $S_{B(3+1)}$ and $S_{B(4+1)}$ independent on particle’s mass are consistent with the thermodynamical entropies $S_{\mathrm{BH}(3+1)}$ and $S_{\mathrm{BH}(4+1)}$, respectively. There is a very visible degree of uniformity between thermodynamics and quantum tunneling in $z=4$ Hořava-Lifshitz gravity. The entropies contained corrected terms could be explained well by the self-gravitational interaction of Hawking radiation. The study of the tunneling process may shed light on understanding the Hořava-Lifshitz gravity.

The purpose of this paper is to extend the analysis presented in Goswami et al. [Phys. Rev. Lett. 96, 031302 (2006)] by means of investigating how a specific type of loop (quantum) effect can alter the outcome of gravitational collapse. To be more concrete, a particular class of spherically symmetric spacetime is considered with a tachyon field $\varphi$ and a barotropic fluid constituting the matter content; the tachyon potential $V(\varphi )$ is assumed to be of the form ${\varphi }^{-2}$. Within inverse triad corrections, we then obtain, for a semiclassical description, several classes of analytical as well as numerical solutions. Moreover, we identify a subset whose behavior corresponds to an outward flux of energy, thus avoiding either a naked singularity or a black hole formation.

Recently discovered models of ghost-free massive gravity and bigravity are characterized by a nontrivial potential that gives rise to a rich vacuum structure. We review maximally symmetric vacua of the de Rham-Gabadadze-Tolley (dRGT) massive gravity and of the Hassan-Rosen (HR) bigravity and discuss their perturbative stability. In particular, we discuss perturbations about self-accelerating vacua in HR bigravity and argue that, analogously to what was found in the case of dRGT gravity, some of them contain strongly coupled modes. We then show that it is impossible to construct regular instantons connecting different classically stable vacua of dRGT gravity without violating energy conservation or the null energy condition.

We study future observational constraints on cosmic string parameters from various types of next-generation experiments: direct detection of gravitational waves (GWs), pulsar timing array, and the cosmic microwave background. We consider both GW burst and stochastic GW background searches by ground- and space-based interferometers as well as GW background detection in pulsar timing experiments. We also consider cosmic string contributions to the cosmic microwave background temperature and polarization anisotropies. These different types of observations offer independent probes of cosmic strings and may enable us to investigate cosmic string properties if the signature is detected. In this paper, we evaluate the power of future experiments to constrain cosmic string parameters, such as string tension $G\mu$, initial loop size $\alpha$, and reconnection probability $p$, by performing Fisher information matrix calculations. We find that combining the information from the different types of observations breaks parameter degeneracies and provides more stringent constraints on the parameters. We also find future space-borne interferometers independently provide a highly precise determination of the parameters.

The statistics of dark matter halos is an essential component of understanding the nonlinear evolution in modified gravity cosmology. Based on a series of modified gravity $N$-body simulations, we investigate the halo mass function, concentration, and bias. We model the impact of modified gravity by a single parameter $\zeta$, which determines the enhancement of particle acceleration with respect to general relativity (GR), given the identical mass distribution ($\zeta =1$ in GR). We select snapshot redshifts such that the linear matter power spectra of different gravity models are identical, in order to isolate the impact of gravity beyond modifying the linear growth rate. At the baseline redshift corresponding to $z_S=1.2$ in the standard $\Lambda \mathrm{CDM}$, for a 10% deviation from GR ($|\zeta -1|=0.1$), the measured halo mass function can differ by about 5%–10%, the halo concentration by about 10%–20%, while the halo bias differs significantly less. These results demonstrate that the halo mass function and/or the halo concentration are sensitive to the nature of gravity and may be used to make interesting constraints along this line.