We employ both top-down and bottom-up holographic dual models of QCD to calculate vertex functions and couplings that are induced by the five-dimensional Chern-Simons term. We use these couplings to study the photoproduction of $f_1$ mesons. The Chern-Simons-term-induced interaction leads to a simple relation between the polarization of the incoming photon and the final state $f_1$ meson which should allow a clear separation of this interaction from competing processes.

The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction $\overline{f}p\to e^{+}n$, where $f$ is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the $f$ lifetime and its decays which produce visible $\gamma$ rays or electrons. We find one operator which would allow $\overline{f}p\to e^{+}n$ at interesting rates in neutrino detectors, as long as $m_f\lesssim m_{\pi }$. The existing constraints on light dark matter from relic density arguments, supernova cooling rates, and big-bang nucleosynthesis are then reviewed. We calculate the cross section for $\overline{f}p\to e^{+}n$ in neutrino detectors implied by this operator, and find that Super-Kamiokande can probe the new physics scale $\Lambda$ for this interaction up to $\mathcal{O}(100\mathrm{TeV})$.

We study large-distance contributions to the nucleon’s parton densities in the transverse coordinate (impact parameter) representation based on generalized parton distributions (GPDs). Chiral dynamics generates a distinct component of the partonic structure, located at momentum fractions $x\lesssim M_{\pi }/M_N$ and transverse distances $b\sim 1/M_{\pi }$. We calculate this component using phenomenological pion exchange with a physical lower limit in $b$ (the transverse “core” radius estimated from the nucleon’s axial form factor, $R_{\mathrm{core}}=0.55\mathrm{fm}$) and demonstrate its universal character. This formulation preserves the basic picture of the “pion cloud” model of the nucleon’s sea quark distributions, while restricting its application to the region actually governed by chiral dynamics. It is found that (a) the large-distance component accounts for only $\sim 1/3$ of the measured antiquark flavor asymmetry $\overline{d}-\overline{u}$ at $x\sim 0.1$; (b) the strange sea quarks $s$ and $\overline{s}$ are significantly more localized than the light antiquark sea; (c) the nucleon’s singlet quark size for $x<0.1$ is larger than its gluonic size, $⟨b^2{⟩}_{q+\overline{q}}>⟨b^2{⟩}_g$, as suggested by the $t$-slopes of deeply-virtual Compton scattering and exclusive $J/\psi$ production measured at HERA and FNAL. We show that our approach reproduces the general $N_c$-scaling of parton densities in QCD, thanks to the degeneracy of $N$ and $\Delta$ intermediate states in the large-$N_c$ limit. We also comment on the role of pionic configurations at large longitudinal distances and the limits of their applicability at small $x$.

We formulate a new algorithm for obtaining the effective continuum threshold in vacuum-to-bound-state correlators—the basic objects for the calculation of hadron form factors in the method of light-cone sum rules in QCD. The effective continuum threshold is one of the key ingredients of the method which to a large extent determines the value of the form factor extracted from the relevant correlator. In a quantum-mechanical potential model, where the exact form factor is known, the application of our algorithm is shown to lead to a dramatic increase of the accuracy of the extracted form factor compared to the standard procedures adopted in the method of sum rules in QCD. Moreover, the application of our algorithm considerably enlarges the range of the momentum transfer where the form factor may be extracted from the correlator.

We implement Dirac neutrinos in the minimal custodial Randall-Sundrum setting via the Krauss-Wilczek mechanism. We demonstrate by giving explicit lepton mass matrices that with neutrinos in the normal hierarchy, lepton mass and mixing patterns can be naturally reproduced at the scale set by the constraints from electroweak precision measurements, and at the same time without violating bounds set by lepton flavor violations. Our scenario generically predicts a nonzero neutrino mixing angle ${\theta }_{13}$, as well as the existence of sub-TeV right-handed Kaluza-Klein neutrinos, which partner the right-handed standard model charged leptons. These relatively light KK neutrinos may be searched for at the LHC.

We present new lattice results of the $K\to \pi \ell \nu$ semileptonic form factors obtained from simulations with two flavors of dynamical twisted-mass fermions, using pion masses as light as 260 MeV. Our main result is $f_{+}(0)=0.9560(84)$, which, combined with the latest experimental data for $K_{\ell 3}$ decays, leads to $|V_{us}|=0.2267(5{)}_{\exp }(20{)}_{f_{+}(0)}$. Using the PDG(2008) determinations of $|V_{ud}|$ and $|V_{ub}|$ our result implies for the unitarity relation $|V_{ud}{|}^2+|V_{us}{|}^2+|V_{ub}{|}^2=1.0004(15)$. For the $O(p^6)$ term of the chiral expansion of $f_{+}(0)$ we get $\Delta f\equiv f_{+}(0)-1-f_2=-0.0214(84)$.

We report a measurement of the longitudinal double-spin asymmetry $A_{LL}$ and the differential cross section for inclusive ${\pi }^0$ production at midrapidity in polarized proton collisions at $\sqrt{s}=200\mathrm{GeV}$. The cross section was measured over a transverse momentum range of $1<p_T<17\mathrm{GeV}/c$ and found to be in good agreement with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry was measured in the range of $3.7<p_T<11\mathrm{GeV}/c$ and excludes a maximal positive gluon polarization in the proton. The mean transverse momentum fraction of ${\pi }^0$’s in their parent jets was found to be around 0.7 for electromagnetically triggered events.

We consider stability of spherically symmetric solutions in $f(R)$ gravity model proposed by Starobinsky. We find that the model suffers from a severe fine-tuning problem when applied to compact objects like neutron stars. The problem can be remedied by introducing a cutoff on the mass of the scalar degree of freedom present in the model. A new mass scale associated with neutron stars density is then required for the stabilities of $f(R)$ gravity solutions inside relativistic stars.

In a variety of inflation models the motion of the inflaton may trigger the production of some noninflaton particles during inflation, for example, via parametric resonance or a phase transition. Particle production during inflation leads to observables in the cosmological fluctuations, such as features in the primordial power spectrum and also non-Gaussianities. Here we focus on a prototype scenario with inflaton, $\varphi$, and isoinflaton, $\chi$, fields interacting during inflation via the coupling $g^2(\varphi -{\varphi }_0{)}^2{\chi }^2$. Since several previous investigations have hinted at the presence of localized “glitches” in the observed primordial power spectrum, which are inconsistent with the simplest power-law model, it is interesting to determine the extent to which such anomalies can be explained by this simple and microscopically well-motivated inflation model. Our prototype scenario predicts a bumplike feature in the primordial power spectrum, rather than an oscillatory “ringing” pattern as has previously been assumed. We discuss the observational constraints on such features using a variety of cosmological data sets. We find that bumps with amplitudes as large as $\mathcal{O}(10\%)$ of the usual scale-invariant fluctuations from inflation, corresponding to $g^2\sim 0.01$, are allowed on scales relevant for cosmic microwave background experiments. Our results imply an upper limit on the coupling $g^2$ (for a given ${\varphi }_0$) which is crucial for assessing the detectability of the non-Gaussianity produced by inflationary particle production. We also discuss more complicated features that result from superposing multiple instances of particle production. Finally, we point to a number of microscopic realizations of this scenario in string theory and supersymmetry and discuss the implications of our constraints for the popular brane/axion monodromy inflation models.

We study the density driven symmetry breaking in holographic superconductors by considering the positive mass squared case. We show that even for the positive $m^2$, a scalar condensation still forms, provided the chemical potential is high enough. As $m^2$ increases, the phase space folds due to the nonlinearity of the equations of motion, and two nearby points in the phase space can represent symmetry breaking and preserving configurations, respectively. The phase space defined by the set of initial conditions of field variables at the horizon undergoes a nonlinear radial evolution to result in the phase space folding, a characteristic phenomenon in a nonlinear system. We then calculate the specific heat, which characterizes superconductors and has been measured in experiments. We observe a discontinuity in the specific heat at the transition point and compare our results with experimentally observed numbers. The electrical conductivity for various $m^2$ is also calculated.

Detailed dependence of resonant spin-flavor (RSF) conversion of supernova neutrinos on electron mole fraction $Y_e$ is investigated. Supernova explosion forms a hot-bubble and neutrino-driven wind region of which electron mole fraction exceeds 0.5 in several seconds after the core collapse. When a higher resonance of the RSF conversion is located in the innermost region, flavor change of the neutrinos strongly depends on the sign of $1-2Y_e$. At an adiabatic high RSF resonance the flavor conversion of ${\overline{\nu }}_e\leftrightarrow {\nu }_{\mu ,\tau }$ occurs in $Y_e<0.5$ and normal mass hierarchy or in $Y_e>0.5$ and inverted mass hierarchy. In other cases of $Y_e$ values and mass hierarchies, the conversion of ${\nu }_e\leftrightarrow {\overline{\nu }}_{\mu ,\tau }$ occurs. The final ${\overline{\nu }}_e$ spectrum is evaluated in the cases of $Y_e<0.5$ and $Y_e>0.5$ taking account of the RSF conversion. Based on the obtained result, time variation of the event number ratios of low ${\overline{\nu }}_e$ energy to high ${\overline{\nu }}_e$ energy is discussed. In normal mass hierarchy, an enhancement of the event ratio should be seen in the period when the electron fraction in the innermost region exceeds 0.5. In inverted mass hierarchy, on the other hand, a dip of the event ratio should be observed. Therefore, the time variation of the event number ratio is useful to investigate the effect of the RSF conversion.

We study all tree-level split helicity gluon amplitudes by using the recently proposed Britto-Cachazo-Feng-Witten recursion relation and Hodges diagrams in ambitwistor space. We pick out the contributing diagrams and find that all of them can be divided into triangles in a suitable way. We give the explicit expressions for all of these amplitudes. As an example, we reproduce the six-gluon split next-to-maximally-helicity-violating amplitudes in momentum space.

We study the evolution of a particular class of nonperiodic cosmic string loops containing Y-junctions, such as may form during the evolution of a network of $(p,q)$ cosmic superstrings. We set up and solve the Nambu-Goto equations of motion for a loop with junctions, focusing attention on a specific initially static and planar loop configuration. After a given time, the junctions collide and the Nambu-Goto description breaks down. We also study the same loop configuration in a $\mathrm{U}(1)\times \mathrm{U}(1)$ gauge field-theory model that allows composite vortices with corresponding Y-junctions. We show that the field-theory and Nambu-Goto evolution are remarkably similar until the collision time. However, in the field-theory evolution a new phenomenon occurs: the composite vortices can unzip, producing in the process new Y-junctions, whose separation may grow significantly, destabilizing the configuration. In particular, an initial loop with two Y-junctions may evolve to a configuration with six Y-junctions (all distinct from each other). Setting up this new configuration as an initial condition for Nambu-Goto strings, we solve for its evolution and establish conditions under which it is stable to the decay mode seen in the field-theory case. Remarkably, the condition closely matches that seen in the field-theory simulations, and is expressed in terms of simple parameters of the Nambu-Goto system. This implies that there is an easy way to understand the instability in terms of which region of parameter space leads to stable or unstable unzippings.

We discuss the renormalization of the initial value problem in quantum field theory using the two-particle irreducible (2PI) effective action formalism. The nonequilibrium dynamics is renormalized by counterterms determined in equilibrium. We emphasize the importance of the appropriate choice of initial conditions and go beyond the Gaussian initial density operator by defining self-consistent initial conditions. We study the corresponding time evolution and present a numerical example which supports the existence of a continuum limit for this type of initial conditions.

Two complementary techniques are developed for obtaining the asymptotic form of gravitational-wave data at large radii from numerical simulations, in the form of easily implemented algorithms. It is shown that, without extrapolation, near-field effects produce errors in extracted waveforms that can significantly affect LIGO data analysis. The extrapolation techniques are discussed in the context of Newman-Penrose data applied to extrapolation of waveforms from an equal-mass, nonspinning black-hole binary simulation. The results of the two methods are shown to agree within error estimates. The various benefits and deficiencies of the methods are discussed.

We apply a dressed perturbation theory to better organize and economize the computation of high orders of the 2-body effective action of an inspiralling post-Newtonian (PN) gravitating binary. We use the effective field theory approach with the nonrelativistic field decomposition (NRG fields). For that purpose we develop quite generally the dressing theory of a nonlinear classical field theory coupled to pointlike sources. We introduce dressed charges and propagators, but unlike the quantum theory there are no dressed bulk vertices. The dressed quantities are found to obey recursive integral equations which succinctly encode parts of the diagrammatic expansion, and are the classical version of the Schwinger-Dyson equations. Actually, the classical equations are somewhat stronger since they involve only finitely many quantities, unlike the quantum theory. Classical diagrams are shown to factorize exactly when they contain nonlinear worldline vertices, and we classify all the possible topologies of irreducible diagrams for low loop numbers. We apply the dressing program to our post-Newtonian case of interest. The dressed charges consist of the dressed energy-momentum tensor after a nonrelativistic decomposition, and we compute all dressed charges (in the harmonic gauge) appearing up to 2PN in the 2-body effective action (and more). We determine the irreducible skeleton diagrams up to 3PN and we employ the dressed charges to compute several terms beyond 2PN.

In a given path with multiple branches, in principle, it can be expected that there are some fork points, where one branch is bifurcated into different branches, or various branches converge into one or several branches. In this paper, it is shown that if there is a web formed by such branches in a given field space, in which each branch can be responsible for a period of slow roll inflation, a multiverse separated by a domain wall network will come into being, some of which might correspond to our observable universe. We discuss this scenario and show possible observations of a given observer at late time.

We show that the initial field values required to produce inflation in the two fields original hybrid model, and its supergravity F-term extension, do not suffer from any fine-tuning problem, even when the fields are restricted to be sub-Planckian and for almost all potential parameter values. This is due to the existence of an initial slow-roll violating evolution which has been overlooked so far. Because of the attractor nature of the inflationary valley, these trajectories end up producing enough accelerated expansion of the Universe. By numerically solving the full nonlinear dynamics, we show that the set of such successful initial field values is connected, of dimension 2 and possesses a fractal boundary of infinite length exploring the whole field space. We then perform a Monte-Carlo–Markov-Chain analysis of the whole parameter space consisting of the initial field values, field velocities, and potential parameters. We give the marginalized posterior probability distributions for each of these quantities such that the Universe inflates long enough to solve the usual cosmological problems. Inflation in the original hybrid model and its supergravity version appears to be generic and more probable by starting outside of the inflationary valley. Finally, the implication of our findings in the context of the eternal inflationary scenario are discussed.

Interpretations of indirect searches for dark matter (DM) require theoretical predictions for the annihilation or decay rates of DM into stable particles of the standard model. These predictions include usually only final states accessible as lowest order tree-level processes, with electromagnetic bremsstrahlung and the loop-suppressed two gamma-ray line as exceptions. We show that this restriction may lead to severely biased results for DM tailored to produce only leptons in final states and with mass in the TeV range. For such models, unavoidable electroweak bremsstrahlung of $Z$ and $W$-bosons has a significant influence both on the branching ratio and the spectral shape of the final state particles. We work out the consequences for two situations: First, the idealized case where DM annihilates at tree level with 100% branching ratio into neutrinos. For a given cross section, this leads eventually to “minimal yields” of photons, electrons, positrons, and antiprotons. Second, the case where the only allowed two-body final states are electrons. The latter case is typical of models aimed at fitting cosmic ray $e^{-}$ and $e^{+}$ data. We find that the multimessenger signatures of such models can be significantly modified with respect to results presented in the literature.

The “improved dynamics” of loop quantum cosmology is extended to include the Bianchi type II model. Because these space-times admit both anisotropies and nonzero spatial curvature, certain technical difficulties arise over and above those encountered in the analysis of the (anisotropic but spatially flat) Bianchi type I space-times and of the (spatially curved but isotropic) $k=\pm 1$ models. We address these and show that the big-bang singularity is resolved in the same precise sense as in the recent analysis of the Bianchi I model. Bianchi II space-times are of special interest to quantum cosmology because of the expected behavior of the gravitational field near generic spacelike singularities in classical general relativity.