We extend our recent derivation of the time evolution equations for the energy content of magnetic fields and turbulent motions for incompressible, homogeneous, and isotropic turbulence to include the case of nonvanishing helicity. These equations are subsequently numerically integrated in order to predict the present day primordial magnetic field strength and correlation length, depending on its initial helicity and magnetic energy density. We find that all prior analytic predictions for helical magnetic fields, such as the epoch when they become maximally helical and their subsequent growth of correlation length $L\sim a^{1/3}$ and decrease of magnetic field strength $B\sim a^{-1/3}$ with scale factor $a$, are well confirmed by the simulations. An initially fully helical primordial magnetic field is a factor $4\times {10}^4$ stronger at the present epoch than its nonhelical counterpart when generated during the electroweak epoch.

Accurate parameter estimation of gravitational waves from coalescing compact binary sources is a key requirement for gravitational-wave astronomy. Evaluating the posterior probability density function of the binary’s parameters (component masses, sky location, distance, etc.) requires computing millions of waveforms. The computational expense of parameter estimation is dominated by waveform generation and scales linearly with the waveform computational cost. Previous work showed that gravitational waveforms from nonspinning compact binary sources are amenable to a truncated singular value decomposition, which allows them to be reconstructed via interpolation at fixed computational cost. However, the accuracy requirement for parameter estimation is typically higher than for searches, so it is crucial to ascertain that interpolation does not lead to significant errors. Here we provide a proof of principle to show that interpolated waveforms can be used to recover posterior probability density functions with negligible loss in accuracy with respect to noninterpolated waveforms. This technique has the potential to significantly increase the efficiency of parameter estimation.

We analyze the MeV/GeV emission from four bright gamma-ray bursts (GRBs) observed by the Fermi Large Area Telescope to produce robust, stringent constraints on a dependence of the speed of light in vacuo on the photon energy (vacuum dispersion), a form of Lorentz invariance violation (LIV) allowed by some quantum gravity (QG) theories. First, we use three different and complementary techniques to constrain the total degree of dispersion observed in the data. Additionally, using a maximally conservative set of assumptions on possible source-intrinsic, spectral-evolution effects, we constrain any vacuum dispersion solely attributed to LIV. We then derive limits on the QG energy scale (the energy scale where LIV-inducing QG effects become strong, $E_{\mathrm{QG}}$) and the coefficients of the Standard Model Extension. For the subluminal case (where high-energy photons propagate more slowly than lower-energy photons) and without taking into account any source-intrinsic dispersion, our most stringent limits (at 95% C.L.) are obtained from GRB 090510 and are $E_{\mathrm{QG},1}>7.6$ times the Planck energy ($E_{\mathrm{Pl}}$) and $E_{\mathrm{QG},2}>1.3\times {10}^{11}\mathrm{GeV}$ for linear and quadratic leading-order LIV-induced vacuum dispersion, respectively. These limits improve the latest constraints by Fermi and H.E.S.S. by a factor of $\sim 2$. Our results disfavor any class of models requiring $E_{\mathrm{QG},1}\lesssim E_{\mathrm{Pl}}$.

A nonsupersymmetric model of a two-loop radiative seesaw is proposed. The model contains, in addition to the standard model Higgs boson, an inert $SU(2{)}_L$ doublet scalar $\eta$ and two inert singlet scalars $\varphi$ and $\chi$. The lepton number is softly broken by a dimension-two operator, and the tree-level mass of the left-handed neutrino is forbidden by $Z_2\times Z_2^{\prime }$ (or $D_{2N}$), which predicts the existence of two or three dark matter particles. The scalar sector is minimal; none of the scalar fields can be suppressed for the radiative seesaw mechanism to work. There are by-products: The standard model Higgs boson decay into two $\gamma$’s is slightly enhanced by ${\eta }^{+}$ (the charged component of $\eta$) circulating in one-loop diagrams for $h\to \gamma \gamma$. The 135 GeV $\gamma$-ray line observed at the Fermi LAT can be also explained by the annihilation of $\chi$ dark matter. We employ a mechanism of temperature-dependent annihilation cross section to suppress the continuum $\gamma$ rays and the production of antiprotons. The explanation can survive even down to the XENON1T sensitivity limit.

Direct searches for light dark matter particles ($\mathrm{\text{mass}}<10\mathrm{GeV}$) are especially challenging because of the low energies transferred in elastic scattering to typical heavy nuclear targets. We investigate the possibility of using liquid helium-4 as a target material, taking advantage of the favorable kinematic matching of the helium nucleus to light dark matter particles. Monte Carlo simulations are performed to calculate the charge, scintillation, and triplet helium molecule signals produced by recoil He ions, for a variety of energies and electric fields. We show that excellent background rejection might be achieved based on the ratios between different signal channels. The sensitivity of the helium-based detector to light dark matter particles is estimated for various electric fields and light collection efficiencies.

The recently discovered scalar resonance at the Large Hadron Collider is now almost confirmed to be a Higgs boson, whose $CP$ properties are yet to be established. At the International Linear Collider with and without polarized beams, it may be possible to probe these properties at high precision. In this work, we study the possibility of probing departures from the pure $CP$-even case, by using the decay distributions in the process $e^{+}{e}^{-}\to t\overline{t}\Phi$, with $\Phi$ mainly decaying into a $b\overline{b}$ pair. We have compared the case of a minimal extension of the Standard Model case (model I) with an additional pseudoscalar degree of freedom, with a more realistic case namely the $CP$-violating two-Higgs doublet model (model II) that permits a more general description of the couplings. We have considered the International Linear Collider with $\sqrt{s}=800\mathrm{GeV}$ and integrated luminosity of $300{\mathrm{fb}}^{-1}$. Our main findings are that even in the case of small departures from the $CP$-even case, the decay distributions are sensitive to the presence of a $CP$-odd component in model II, while it is difficult to probe these departures in model I unless the pseudoscalar component is very large. Noting that the proposed degrees of beam polarization increase the statistics, the process demonstrates the effective role of beam polarization in studies beyond the Standard Model. Further, our study shows that an indefinite $CP$ Higgs would be a sensitive laboratory to physics beyond the Standard Model.

Precision measurement of the leptonic $CP$ violating phase $\delta$ will suffer from the, then surviving, large uncertainty of ${sin}^2{\theta }_{23}$ of 10–20% in the experimentally interesting region near maximal mixing of ${\theta }_{23}$. We advocate a new method for determination of both ${\theta }_{23}$ and $\delta$ at the same time using only the ${\nu }_e$ and ${\overline{\nu }}_e$ appearance channels and show that ${sin}^2{\theta }_{23}$ can be determined automatically with much higher accuracy, approximately a factor of six, than $\sin \delta$. In this method, we identify a new degeneracy for the simultaneous determination of ${\theta }_{23}$ and $\delta$, the ${\theta }_{23}$ intrinsic degeneracy, which must be resolved in order to achieve precision measurement of these two parameters. Spectral information around the vacuum oscillation maxima is shown to be the best way to resolve this degeneracy.

The effects of $CP$-violating phases in active-sterile solar neutrino oscillations are discussed in a general scheme of $3+N_s$ mixing, without any constraint on the mixing between the three active and the $N_s$ sterile neutrinos, assuming only a realistic hierarchy of neutrino mass-squared differences. A generalized Parke formula describing the neutrino oscillation probabilities inside the Sun is calculated. The validity of the analytical calculation and the probability variation due to the unknown $CP$-violating phases are illustrated with a numerical calculation of the evolution equation in the case of $3+1$ neutrino mixing.

The seesaw mechanism can be generalized to a type-III variant and a quintuplet variant. We present two models that provide analogous generalizations of the inverse seesaw mechanism. The first model employs a real fermion triplet $\mathcal{F}\sim (1,3,0)$ and requires no additional multiplets or parameters relative to the standard inverse seesaw. We argue that, from a bottom-up perspective, there appears to be no particular reason to preference the usual scenario over this variant. The second model employs a fermion quintuplet $\mathcal{F}\sim (1,5,0)$ and requires an additional scalar $S\sim (1,4,1)$. We also show that minimal inverse seesaws with even larger fermionic representations are not expected to realize naturally small neutrino masses.

The integrated and differential fiducial cross sections for the production of a $W$ or $Z$ boson in association with a high-energy photon are measured using $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$. The analyses use a data sample with an integrated luminosity of $4.6{\mathrm{fb}}^{-1}$ collected by the ATLAS detector during the 2011 LHC data-taking period. Events are selected using leptonic decays of the $W$ and $Z$ bosons [$W(e\nu ,\mu \nu )$ and $Z(e^{+}{e}^{-},{\mu }^{+}{\mu }^{-},\nu \overline{\nu })$] with the requirement of an associated isolated photon. The data are used to test the electroweak sector of the Standard Model and search for evidence for new phenomena. The measurements are used to probe the anomalous $WW\gamma$, $ZZ\gamma$, and $Z\gamma \gamma$ triple-gauge-boson couplings and to search for the production of vector resonances decaying to $Z\gamma$ and $W\gamma$. No deviations from Standard Model predictions are observed and limits are placed on anomalous triple-gauge-boson couplings and on the production of new vector meson resonances.

In this work the pure spinor formulation of the superstring is used to study quantum corrections to the left current operator product expansion algebra of the coset $\mathrm{PSU}(2,2|4)/\mathrm{SO}(4,1)\times \mathrm{SO}(5)$ sigma model, which describes the superstring dynamics in the ${\mathrm{AdS}}_5\times {\mathrm{S}}^5$ background. In particular, the one-loop corrections to the simple poles of the bosonic currents are computed. Unlike the case of the double poles, we show that the simple poles suffer corrections, which are important since the simple poles contribute to the four-point amplitudes. We show that the only contribution to the simple poles comes from the pure spinor Lorentz currents.

In this work we study the contribution to leptogenesis from $\Delta L=1$ decay and scattering processes mediated by the Higgs with quarks in the initial and final states using the formalism of nonequilibrium quantum field theory. Starting from fundamental equations for correlators of the quantum fields we derive quantum-corrected Boltzmann and rate equations for the total lepton asymmetry improved in that they include quantum-statistical effects and medium corrections to the quasiparticle properties. To compute the collision term we take into account one- and two-loop contributions to the lepton self-energy and use the extended quasiparticle approximation for the Higgs two-point function. The resulting $CP$-violating and washout reaction densities are numerically compared to the conventional ones.

We study motion of an electric current-carrying string loop oscillating in the vicinity of the Schwarzschild black hole immersed in an external uniform magnetic field. The dependence of boundaries and different types of motion of the string loop on magnetic field strength is found. The dynamics of the string loop in the Cartesian $xy$ plane depends both on value and direction of the magnetic field and current. It is shown that the magnetic field influence on the behavior of the string loop is quite significant even for weak magnetic field strength. The oscillation of the string loop becomes stronger or weaker in dependence on the direction of the Lorenz force. We illustrate the various regimes of the trajectories of the string loop that can fall down into the black hole, escape to infinity, or be trapped in the finite region near the horizon for the different representative values of the magnetic field. We have also considered the flat spacetime limit as the condition of the escape of the string loop from the neighborhood of the black hole to infinity. We found the expression for the magnetic field strength for which the oscillatory motion of the string loop totally vanishes and the string loop can have maximal acceleration in the perpendicular direction to the plane of the loop.

In this work, we study the chiral symmetry breaking in pseudo-quantum electrodynamics in ($2+1$) dimensions, which is designed to reproduce a Coulomb potential for charged particles on a plane interacting via photons propagating in ($3+1$) space-time dimensions and would be relevant for applications to condensed-matter systems. Using an ultraviolet cutoff in the momentum integrals, we show that there is a critical dimensionless coupling ${\alpha }_c=\pi /4$ above which there is chiral symmetry breaking. In the case of the theory with $N$ massless fermions, we obtain a critical value of the number of fermion flavors, $N_c$, below which the chiral symmetry breaking occurs. Finally, we discuss the relevance of our results to graphene in the ultimate deep infrared regime where the Fermi velocity of the Dirac fermions approaches the velocity of light.

The general boundary formulation of quantum field theory is applied to a massive scalar field in two-dimensional Rindler space. The field is quantized according to both the Schrödinger-Feynman quantization prescription and the holomorphic one in two different spacetime regions: a region bounded by two Cauchy surfaces and a region bounded by one timelike curve. An isomorphism is constructed between the Hilbert spaces associated with these two boundaries. This isomorphism preserves the probabilities that can be extracted from the free and the interacting quantum field theories, proving the equivalence of the $S$-matrices defined in the two settings, when both apply.

We extend our investigation of soft graviton effects on the microscopic dynamics of matter fields in de Sitter space. We evaluate the quantum equation of motion in generic gauge theories. We find that the Lorentz invariance can be respected and the velocity of light is not renormalized at the one-loop level. The gauge coupling constant is universally screened by soft gravitons and diminishes with time. These features are in common with other four-dimensional field theories with dimensionless couplings. In particular, the couplings scale with time with definite scaling exponents. Although individual scaling exponents are gauge dependent, we argue that the relative scaling exponents are gauge independent and should be observable. We also mention soft graviton effects on cosmic microwave background.

Gravitational-wave searches for signals from inspiraling compact binaries have relied on matched filtering banks of waveforms (called template banks) to try to extract the signal waveforms from the detector data. These template banks have been constructed using four main considerations, the region of parameter space of interest, the sensitivity of the detector, the matched filtering bandwidth, and the sensitivity one is willing to lose due to the granularity of template placement, the latter of which is governed by the minimal match. In this work we describe how the choice of the lower frequency cutoff, the lower end of the matched filter frequency band, can be optimized for detection. We also show how the minimal match can be optimally chosen in the case of limited computational resources. These techniques are applied to searches for binary neutron star signals that have been previously performed when analyzing Initial LIGO and Virgo data and will be performed analyzing Advanced LIGO and Advanced Virgo data using the expected detector sensitivity. By following the algorithms put forward here, the volume sensitivity of these searches is predicted to improve without increasing the computational cost of performing the search.

I examine the idea that our world is a branelike object of negligible influence on the bulk spacetime. No particular action functional is specified. Instead, the probe brane dynamics is derived from the universally valid stress-energy conservation equations. As an example, I study the case of a three-sphere in the five-dimensional Minkowski spacetime. The resulting four-universe turns out to depend on the equation of state of the brane constituent matter but differs from that of general relativity. One observes that, for every general relativistic universe, there exists a brane universe of equal geometry but a slightly different equation of state. As for the stability of brane universes, I find that no equation of state leads to a stable solution. However, the situation changes if the bulk spacetime has a Euclidean signature. In this case, a class of stable cosmological solutions is obtained. The brane vibrations are guided by the covariant Klein-Gordon equation with an effective metric of the Minkowski signature. It is this effective metric that local observers actually detect. As a consequence, the detected Universe is of bouncing type, with an accelerating expanding phase.

We calculate emission rates of various bosonic/fermionic soft massless states of an open/closed superstring from an ensemble of a highly excited open/closed superstring in the flat background. The resulting spectrum shows thermal distributions at the Hagedorn temperature. We find greybody factors for each process and observe their relation to the ones from black holes.

We obtain the exact renormalization group flow equation for a self-interacting real scalar field in an expanding cosmological background. The beta functional for the potential in the local potential approximation is determined in terms of the mode functions defining the vacuum of the theory. For a scalar in an inflating Universe, which is released in the Bunch-Davies vacuum, the flow equation is analyzed in detail using the optimized cutoff function for the quartically truncated potential. In that case, the constant term in the potential, which can in fact be viewed as the cosmological constant, decreases as the IR cutoff is removed, supporting the existence of a quantum mechanical screening mechanism. On the other hand, the running of the quartic coupling constant at IR is altered by the expansion, which seems to affect the quantum triviality of the theory.