A variational method is discussed, based on the principle of minimal variance. The method seems to be suited for gauge interacting fermions, and the simple case of quantum electrodynamics is discussed in detail. The issue of renormalization is addressed, and the renormalized propagators are shown to be the solution of a set of finite integral equations. The method is proven to be viable, and, by a spectral representation, the multidimensional integral equations are recast in one-dimensional equations for the spectral weights. The UV divergences are subtracted exactly, yielding a set of coupled Volterra integral equations that can be solved iteratively and are known to have a unique solution.

We demonstrate for the first time a search pipeline with improved sensitivity to gravitational waves from coalescing binary black holes with spins aligned to the orbital angular momentum by the inclusion of spin effects in the search templates. We study the pipeline recovery of simulated gravitational wave signals from aligned-spin binary black holes added to real detector noise, comparing the pipeline performance with aligned-spin filter templates to the same pipeline with nonspinning filter templates. Our results exploit a three-parameter phenomenological waveform family that models the full inspiral-merger-ringdown coalescence and treats the effect of aligned spins with a single effective spin parameter $\chi$. We construct template banks from these waveforms by a stochastic placement method and use these banks as filters in the recently developed gstlal search pipeline. We measure the observable volume of the analysis pipeline for binary black hole signals with $M_{\text{total}}$ and $\chi \in [0,0.85]$. We find an increase in observable volume of up to 45% for systems with $0.2\le \chi \le 0.85$ with almost no loss of sensitivity to signals with $0\le \chi \le 0.2$. We also show that the use of spinning templates in the search pipeline provides for more accurate recovery of the binary mass parameters as well as an estimate of the effective spin parameter. We demonstrate this analysis on 25.9 days of data obtained from the Hanford and Livingston detectors in LIGO’s fifth observation run.

We explore the properties of two-point cosmic propagators when perturbation theory loop corrections are consistently taken into account. We show in particular how the interpolation scheme proposed in [F. Bernardeau, M. Crocce, and R. Scoccimarro, Phys. Rev. D 85, 123519 (2012)] can be explicitly used up to two-loop order introducing the notion of regular parts for the contributing terms. Extending the one-loop results, we then derive and give semianalytical forms of the two-loop contributions for both the cosmic density and velocity propagators. These results are tested against numerical simulations and shown to significantly improve upon one-loop results for redshifts above 0.5. We found however that at lower redshift two-loop order corrections are too large partly due to a strong sensitivity of those terms to the small scale modes. We show that this dependence is expected to be even larger for higher order loop corrections both from theoretical investigations and numerical tests, the latter obtained with Monte Carlo evaluations of the three-loop contributions. This makes small-scale regularization schemes necessary for the use of such higher order corrections.

We study Chern-Simons black holes in $d$ dimensions and we calculate analytically the quasinormal modes of fermionic perturbations. Also, we consider as background the five-dimensional Chern-Simons black hole with torsion and the BTZ black hole with torsion. We have found that the quasinormal modes depend on the highest power of curvature present in the Chern-Simons theory, such as that which occurs for the quasinormal modes of scalar perturbations. We also show that the effect of the torsion is to modify the real part of the quasinormal frequencies, which modify the oscillation frequency of the field for the five-dimensional case. However, for the BTZ black hole with torsion, the effect is to modify the imaginary part of these frequencies, that is, the relaxation time for the decay of the black hole perturbation. The imaginary part of the quasinormal frequencies is negative, which guarantees the stability of these black holes under fermionic field perturbations.

The thermodynamics of pure glue theories can be described in terms of an effective action for the Polyakov loop. This effective action is of the Landau-Ginzburg type, and its variables are the angles parametrizing the loop. In this paper we compute perturbative corrections to this action. Remarkably, two-loop corrections turn out to be proportional to the one-loop action, independent of the eigenvalues of the loop. By a straightforward generalization of the ’t Hooft coupling, this surprisingly simple result holds for any of the classical and exceptional groups.

We study the anomalous magnetic and electric dipole moments of charged leptons in supersymmetric low-scale seesaw models with right-handed neutrino superfields. We consider a minimally extended framework of minimal supergravity, by assuming that $CP$ violation originates from complex soft SUSY-breaking bilinear and trilinear couplings associated with the right-handed sneutrino sector. We present numerical estimates of the muon anomalous magnetic moment and the electron electric dipole moment, as functions of key model parameters, such as the Majorana mass scale $m_N$ and $\tan \beta$. In particular, we find that the contributions of the singlet heavy neutrinos and sneutrinos to the electron electric dipole moment are naturally small in this model, of order $10^{-27}-10^{-28}e\mathrm{c}\mathrm{m}$, and can be probed in present and future experiments.

I find the three-loop contribution to the effective potential for the Standard Model Higgs field, in the approximation that the strong and top Yukawa couplings are large compared to all other couplings, using dimensional regularization with modified minimal subtraction. Checks follow from gauge invariance and renormalization group invariance. I also briefly comment on the special problems posed by Goldstone boson contributions to the effective potential, and on the numerical impact of the result on the relations between the Higgs vacuum expectation value, mass, and self-interaction coupling.

We argue that classical strings, both bosonic and supersymmetric, can have finite energy and momentum at their endpoints. We show that in a general curved background, string endpoints must propagate along null geodesics as long as their energy remains finite. Finite endpoint momentum allows strings with a fixed energy to travel a greater distance in a five-dimensional anti–de Sitter Schwarzschild background than has been possible for classical solutions considered previously. We review the relevance to heavy ion phenomenology of the dependence of this distance on energy, and we propose a scheme for determining the instantaneous rate of energy loss.

A positron excess up to energies of $\sim 350\mathrm{GeV}$ has been observed by AMS-02, and it is consistent with the positron excess observed by PAMELA up to 100 GeV. There is no observed excess of antiprotons over the expected cosmic ray background. We propose a leptophilic dark matter with an ${U(1)}_{L_{\mu }-L_{\tau }}$ gauge extension of the minimal supersymmetric standard model. The dark matter is an admixture of the $L_{\mu }-L_{\tau }$ gaugino and fermionic partners of the extra $SU(2)$ singlet Higgs boson, which break the $L_{\mu }-L_{\tau }$ symmetry. We construct the $\mathrm{SM}\otimes U{(1)}_{L_{\mu }-L_{\tau }}$ supersymmetry model which provides the correct relic density of dark matter and is consistent with the constraint on $Z^{\prime }$ from LHC. The large dark matter annihilation cross section into ${\mu }^{+}{\mu }^{-}$ and ${\tau }^{+}{\tau }^{-}$, needed to explain PAMELA and AMS-02 results, is achieved by Breit-Wigner resonance.

We consider a quantum scalar field with a $\lambda {\phi }^4$ interaction in curved spacetimes. The quantum effects are taken into account nonperturbatively using the Hartree approximation to the two-particle irreducible effective action. Although this approximation has been considered in many previous works, we reconsider it using a consistent nonperturbative renormalization procedure, which we extend to general curved spacetimes. We obtain the renormalized equations for the mean field and for the propagator of the fluctuations, showing explicitly their independence on the arbitrary scale introduced by the regularization scheme. We apply our results to the particular case of de Sitter spacetime and discuss spontaneous symmetry breaking. The results depend strongly on the renormalization procedure.

What is the right way to interpret a massive graviton? We generalize the kinematical framework of general relativity to multiple connections. The average of the connections is itself a connection and plays the role of the canonical connection in standard general relativity. At the level of dynamics, the simplest choice of the Einstein-Hilbert action is indistinguishable from the single-connection case. However, inspired by Weyl geometry, we show how one can construct massive gravity to all orders in perturbation theory compatible with the de Rham-Gabadadze-Tolley ghost-free model. We conclude that the mass of the graviton can be interpreted as a geometrical property of spacetime arising from two connections. Furthermore, in the multiconnection framework there is no ambiguity in the definition of the physical metric and consequently coupling to matter.

The center of the our Galaxy is a region where very energetic phenomena take place. In particular, powerful cosmic ray sources can be located in that region. The cosmic rays accelerated in these sources may interact with ambient protons and/or low energy photons producing gamma rays and neutrinos. The observation of these two types of secondary particles can be very useful for the identification of the cosmic ray sources and for the understanding of the physical processes occurring during acceleration. Motivated by the excess in the neutrino spectrum recently reported by the IceCube Collaboration, we study in detail the shape of the gamma ray and neutrino spectra originating from the interaction of cosmic ray protons with ambient protons for sources located in the Galactic Center region. We consider different models for proton acceleration and study the impact on the gamma ray and neutrino spectra. We also discuss the possibility to constrain and even identify a particular neutrino source by using the information given by the gamma ray spectrum, taking advantage of the modification of the spectral shape caused by the interaction of the gamma rays with the photons of the radiation field present in the interstellar medium, which strongly depends on the source distance.

In this paper, we detail the thermodynamics of two-flavor nonlocal Polyakov–Nambu–Jona-Lasinio models for different parametrizations of the quark interaction regulators. The structure of the model is upgraded in order to allow for terms in the quark self-energy that violate Lorentz invariance due to the presence of the medium. We examine the critical properties, the phase diagram, and the equation of state. Furthermore, some aspects of the Mott effect for pions and sigma mesons are discussed explicitly within a nonlocal Polyakov–Nambu–Jona-Lasinio model. In particular, we continued the meson polarization function in the complex energy plane. Under certain approximations we were able to extract the imaginary part as a function of the meson energy. We were not able to calculate the dynamical meson mass and therefore resorted to a technical study of the temperature dependence of the meson width by replacing the meson energy with the temperature-dependent spatial meson mass. Our results show that, while the temperature behavior of the meson widths is qualitatively the same for a wide class of covariant regulators, the special case in which the nonlocal interactions are introduced via the instanton liquid model singles out with a drastically different behavior.

The infrared-ultraviolet properties of quantum gravity suggest on very general grounds that hard short distance scattering processes are highly suppressed for center of mass scattering energies beyond the fundamental Planck scale. If this scale is not too far above the electroweak scale, these nonperturbative quantum gravity effects could be manifest as an extinction of high transverse momentum jets at the LHC. To model these effects, we implement an extinction Monte Carlo modification of the PYTHIA event generator based on a Veneziano form factor with a large absorptive branch cut modification of hard QCD scattering processes. Using this we illustrate the leading effects of extinction on the inclusive jet transverse momentum spectrum at the LHC. We estimate that an extinction mass scale of up to roughly half the center of mass beam collision energy could be probed with high statistics data. Experimental searches at the LHC for jet extinction would be complementary to ongoing searches for the related phenomenon of excess production of high multiplicity final states.

The behavior of the quark condensates at zero chemical potential and finite temperature subject to an external magnetic field is studied within the three flavor Nambu–Jona-Lasinio model with Polyakov loop (PNJL) and its extension, the so-called entangled PNJL model (EPNJL). A comparison with recent lattice QCD data is performed and it is shown that at $T=0\mathrm{MeV}$ the light quark condensates are in quantitative agreement. At finite temperature, although there is an overall reasonable agreement with several lattice results, it is shown that in the lattice calculations the effect due to the electric charge quark difference is stronger and the restoration of the $u$ quark chiral symmetry starts at lower temperatures. When considering the entangled PNJL model with a Polyakov loop scale parameter that depends on the magnetic field, it is possible to obtain an earlier rise of the Polyakov loop with the increase of the magnetic field and due to the entanglement, the inverse magnetic catalysis is found as in the lattice QCD calculations.

The strong form factors and coupling constants of $V{D}_{s0}^{*}{D}_{s1}$ and $V{D}_s{D}_s^{*}$ ($V=\varphi$, $J/\psi$) vertices in the framework of the three-point QCD sum rules are considered. Taking into account the nonperturbative part contributions of the correlation functions, the quark-quark, gluon-gluon, and quark-gluon condensate as important terms are evaluated. Considering the $S{U}_f(3)$ symmetry, we compare our results with the values obtained in other methods.

The quantum properties of a helixlike shaped QCD string are studied in the context of the semiclassical Lund fragmentation model. It is shown how simple quantization rules combined with the causality considerations in the string fragmentation process describe the mass hierarchy of light pseudoscalar mesons. The quantized helix string model predicts observable quantum effects related to the threshold behavior of the intrinsic transverse momentum of hadrons, and of the minimal transverse momentum difference between adjacent hadrons. The numerical fit of the properties of the QCD field breaking into ground state hadrons agree with astonishing precision with values obtained recently in the theory of knotted chromoelectric flux tubes.

Proposals for physics beyond the standard model often include new colored particles at or beyond the scale of electroweak symmetry breaking. Any new particle with a sufficient lifetime will bind with standard model gluons and quarks to form a spectrum of new hadrons. Here we focus on colored particles in the octet, decuplet, 27-plet, 28-plet and 35-plet representations of SU(3) color because these can form hadrons without valence quarks. In every case, lattice creation operators are constructed for all angular momentum, parity and charge conjugation quantum numbers. Computations with fully dynamical lattice QCD configurations produce numerical results for mass splittings within this new hadron spectrum. A previous quenched lattice study explored the octet case for certain quantum number choices, and our findings provide a reassessment of those early results.

We study the unintegrated, or transverse momentum dependent gluon distribution obtained from the best description of the LHC data on the inclusive spectra of hadrons produced in the midrapidity region and at low transverse momenta at the starting scale $Q_0^2=1\mathrm{GeV}{}^2$. To extend this gluon density to higher $Q^2$ we apply the Catani-Ciafoloni-Fiorani-Marchesini evolution equation. The influence of the initial (starting) nonperturbative gluon distribution is studied. The application of the obtained gluon density to the analysis of the deep inelastic $ep$ scattering allows us to get the results which describe reasonably well the H1 and ZEUS data on the longitudinal proton structure function $F_L(x,Q^2)$. So, the connection between the soft processes at the LHC and small-$x$ physics at HERA has been confirmed and extended to a wide kinematical region.

We study the dynamics of electroweak bubbles in the scenario of a strong first-order inverse electroweak phase transition at the TeV scale involving the global structure of the nonlinear sigma field in the littlest Higgs model with $T$ parity. Employing the one-loop-order finite-temperature effective potential, we find that the pressure in the symmetric phase, i.e., inside the bubble, is always greater than that in the asymmetric phase, i.e., outside the bubble, so that the bubbles are expanding. By calculating the fluid velocities in the two phases we arrive at the condition of a supersonic deflagrated motion of the bubble walls. We then discuss the generation of gravitational waves from the collisions of such bubbles as well as from the turbulence of the plasma.