The recent results in $\sqrt{s}=2.76\mathrm{TeV}$ $\mathrm{Pb}+\mathrm{Pb}$ collisions at the Large Hadron Collider (LHC) reported by the ALICE collaboration shows that the power-law energy-dependence of charged hadron multiplicity in $\mathrm{Pb}+\mathrm{Pb}$ collisions is significantly different from $\mathrm{p}+\mathrm{p}$ collisions. We show that this different energy-dependence can be explained by inclusion of a strong angular-ordering in the gluon-decay cascade within the color glass condensate (or gluon saturation) approach. This effect is more important in nucleus-nucleus collisions where the saturation scale is larger than 1 GeV. Our prescription gives a good description of the LHC data both in $\mathrm{p}+\mathrm{p}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions.

The ionization of atomic electrons by scattering of neutrinos is revisited. This process is the one studied in the experimental searches for a neutrino magnetic moment using germanium detectors. Current experiments are sensitive to the ionization energy comparable with the atomic energies, and the effects of the electron binding should be taken into account. We find that the so-called stepping approximation to the neutrino-impact ionization is in fact exact in the semiclassical limit and also that the deviations from this approximation are very small already for the lowest bound Coulomb states. We also consider the effects of electron-electron correlations and argue that the resulting corrections to the ionization of independent electrons are quite small. In particular, we estimate that in germanium these are at a 1% level at the energy transfer down to a fraction of keV. Exact sum rules are also presented as well as analytical results for a few lowest hydrogenlike states.

Results are presented from a reanalysis of the entire five-tower data set acquired with the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory, with an exposure of 969 kg-days. The analysis window was extended to a recoil energy of 150 keV, and an improved surface-event background-rejection cut was defined to increase the sensitivity of the experiment to the inelastic dark matter (iDM) model. Three dark matter candidates were found between 25 keV and 150 keV. The probability to observe three or more background events in this energy range is 11%. Because of the occurrence of these events, the constraints on the iDM parameter space are slightly less stringent than those from our previous analysis, which used an energy window of 10–100 keV.

We explicitly construct the fermion propagator in a magnetic field background $B$ to take the lowest Landau-level approximation. We analyze the energy and momentum dependence in the polarization tensor and discuss the collective excitations. We find there appear two branches of collective modes in one of two transverse gauge particles; one represents a massive and attenuated gauge particle and the other behaves similar to the zero sound at finite density.

We study the compression of information present in the correlated perturbations to the luminosity distance in the low-redshift ($z<0.1$) supernovae Ia due to peculiar velocities of these supernovae. We demonstrate that the naïve compression into angular velocity power spectrum does not work efficiently, due to thickness of the spherical shell over which the supernovae are measured. Instead, we show that measurements can be compressed into measurements of $f^{2}P(k)$, where $f$ is the logarithmic rate of growth of linear perturbations and $P(k)$ is their power spectrum. We develop an optimal quadratic estimator and show that it recovers all information for $\Lambda \mathrm{CDM}$ models for surveys of $N\sim 10,000$ or more supernovae. We explicitly demonstrate robustness with respect to the assumed fiducial model and the number of power spectrum bins. Using mock catalogues of supernovae Ia we estimate that future low-redshift surveys will be able to probe ${\sigma }_8$ to 6% accuracy with 10 000 supernovae Ia.

We demonstrate that it is possible to determine the coefficients of an all-orders beta-function linear in the anomalous dimensions using as data the 2-loop coefficients together with the first one of the anomalous dimensions which are universal. The beta function allows us to determine the anomalous dimension of the fermion masses at the infrared fixed point, and the resulting values compare well with the lattice determinations.

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The “underlying event” is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average $p_{\mathrm{T}}$ are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data.

We demonstrate the recent observation of a peak in the dijet invariant mass of the $Wjj$ signal observed by the CDF Collaboration can be explained as the same upward fluctuation observed by CDF in single-top-quark production. In general, both $t$-channel and $s$-channel single-top-quark production produce kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo simulation to subtract the single-top backgrounds instead of data, a peak in the dijet spectrum is expected. The D0 Collaboration has a small upward fluctuation in their published $t$-channel data; and hence we predict they would see at most a small peak in the dijet invariant-mass spectrum of $Wjj$ if they follow the same procedure as CDF.

We propose a scenario to stabilize all geometric moduli—that is, the complex structure, Kähler moduli, and the dilaton—in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with nonperturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized—in the most restrictive case, leaving only one combination of Kähler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate nonperturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous $U(1)$ symmetries, which arise from the required bundle constructions. We present a specific example, with a consistent choice of nonperturbative effects, where all remaining flat directions are stabilized in an anti-de Sitter vacuum.

Because of their explicit construction, Aloff-Wallach spaces are prominent in flux compactifications. They carry $G_2$ structures and admit the $G_2$-instanton equations, which are natural Bogomol’nyi-Prasad-Sommerfeld equations for Yang-Mills instantons on seven-manifolds and extremize a Chern-Simons–type functional. We consider the Chern-Simons flow between different $G_2$ instantons on Aloff-Wallach spaces, which is equivalent to spin(7) instantons on a cylinder over them. For a general SU(3)-equivariant gauge connection, the generalized instanton equations turn into gradient-flow equations on ${\mathbb{C}}^3\times {\mathbb{R}}^2$, with a particular cubic superpotential. For the simplest member of the Aloff-Wallach family (with 3-Sasakian structure) we present an explicit instanton solution of tanh-like shape.

We display several examples of how fields with different limiting velocities (the “speed of light”) at a high energy scale can nevertheless have a common limiting velocity at low energies due to the effects of interactions. We evaluate the interplay of the velocities through the self-energy diagrams and use the renormalization group to evolve the system to low energy. The differences normally vanish only logarithmically, so that an exponentially large energy trajectory is required in order to satisfy experimental constraints. However, we also display a model in which the running is a power-law type, which could be more phenomenologically useful. The largest velocity difference should be in the system with the weakest interaction, which suggests that the study of the speed of gravitational waves would be the most stringent test of this phenomenon.

We investigate the circular motion of charged test particles in the gravitational field of a charged mass described by the Reissner-Nordström spacetime. We study in detail all the spatial regions where circular motion is allowed around either black holes or naked singularities. The effects of repulsive gravity are discussed by finding all the circles at which a particle can have vanishing angular momentum. We show that the geometric structure of stable accretion disks, made of only test particles moving along circular orbits around the central body, allows us to clearly distinguish between black holes and naked singularities.

We study the issue of diffeomorphism symmetry in group field theories (GFT), using the noncommutative metric representation introduced by A. Baratin and D. Oriti [Phys. Rev. Lett. 105, 221302 (2010).]. In the colored Boulatov model for $3d$ gravity, we identify a field (quantum) symmetry which ties together the vertex translation invariance of discrete gravity, the flatness constraint of canonical quantum gravity, and the topological (coarse-graining) identities for the $6j$ symbols. We also show how, for the GFT graphs dual to manifolds, the invariance of the Feynman amplitudes encodes the discrete residual action of diffeomorphisms in simplicial gravity path integrals. We extend the results to GFT models for higher-dimensional $BF$ theories and discuss various insights that they provide on the GFT formalism itself.

We consider black holes localized on the brane in the Randall-Sundrum infinite braneworld model. These configurations are static and charged with respect to a spherically symmetric, electric Maxwell field living on the brane. We start by attempting to construct vacuum black holes, in which case our conclusions are in agreement with those of Yoshino [J. High Energy Phys. 01 (2009) 068]. Although approximate solutions appear to exist for sufficiently small brane tension, these are likely only numerical artifacts. The qualitative features of the configurations in the presence of a brane U(1) electric field are similar to those in the vacuum case. In particular, we find a systematic unnatural behavior of the metric functions in the asymptotic region in the vicinity of the anti–de Sitter horizon. Our results are most naturally interpreted as evidence for the nonexistence of static, nonextremal charged black holes on the brane. In contrast, extremal black holes are more likely to exist on the brane. We determine their near-horizon form by employing both analytical and numerical methods. For any bulk dimension $d>4$, we find good agreement between the properties of large extremal black holes and the predictions of general relativity, with calculable subleading corrections.

We analyze the dynamics of trapped matter shells in spherically symmetric inhomogeneous $\Lambda$-CDM models. The investigation uses a generalized Lemaître-Tolman-Bondi description with initial conditions subject to the constraints of having spatially asymptotic cosmological expansion, initial Hubble-type flow, and a regular initial density distribution. We discuss the effects of shell crossing and use a qualitative description of the local trapped matter shells to explore global properties of the models. Once shell crossing occurs, we find a splitting of the global shells separating expansion from collapse into, at most, two global shells: an inner and an outer limit trapped matter shell. In the case of expanding models, the outer limit trapped matter shell necessarily exists. We also study the role of shear in this process, compare our analysis with the Newtonian framework, and give concrete examples using density profile models of structure formation in cosmology.

Baryon acoustic oscillations imprinted in the galaxy power spectrum can be used as a standard ruler to determine the angular diameter distance and Hubble parameter from high-redshift galaxies. Combining redshift distortion effect which apparently distorts the galaxy clustering pattern, we can also constrain the growth rate of large-scale structure formation. Usually, future forecasts for constraining these parameters from galaxy redshift surveys are made with the full 2D power spectrum characterized as a function of wave number $k$ and directional cosine $\mu$ between line-of-sight direction and wave vector, i.e., $P(k,\mu )$. Here, we apply the multipole expansion to the full 2D power spectrum, and discuss how much cosmological information can be extracted from the lower-multipole spectra, taking a proper account of the nonlinear effects on gravitational clustering and redshift distortion. Fisher matrix analysis reveals that compared to the analysis with the full 2D spectrum, using only the partial information from the monopole and quadrupole spectra generally degrades the constraints by a factor of $\sim 1.3$ for each parameter. The additional information from the hexadecapole spectrum helps to improve the constraints, leading to a result that is almost comparable to the one expected from the full 2D spectrum.

A new statistical method is proposed to coherently combine baryon acoustic oscillation statistics (BAO) and peculiar velocity measurements exploiting decomposed density-density and velocity-velocity spectra in real space from the observed redshift distortions in redshift space, 1) to achieve stronger dark energy constraints, $\sigma (w)=0.06$ and $\sigma (w_a)=0.20$, which are enhanced from BAO or velocity measurements alone, and 2) to cross-check consistency of dark energy constraints from two different approaches; BAO as geometrical measurements and peculiar velocity as large-scale structure formation observables. In addition to those advantages, as power spectra decomposition procedure is free from uncertainty of galaxy bias, this simultaneous fitting is an optimal method to extract cosmological parameters without any preassumption about galaxy bias.

We study the geometric phase (GP) in neutrino oscillation for both Dirac and Majorana neutrinos. We apply the kinematic generalization of the GP to quantum open systems that take into account the coupling to a dissipative environment. In the dissipationless case, the GP does not depend on the Majorana angle. It is not the case in the presence of dissipation and hence the GP can serve as a tool determining the type of the Dirac vs the Majorana neutrino.

The two–equation-of-state model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor Nambu–Jona-Lasinio effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed-current quark masses, the main important effect of the chiral dynamics is the appearance of an end point for the coexistence zone. We show that a first-order hadron-quark phase transition may take place in the region $\mathrm{T}\subset (50–80)\mathrm{MeV}$ and ${\rho }_B\subset (2–4){\rho }_0$, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From the isospin properties of the mixed phase, some possible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of a critical end point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain.

To obtain a well-defined path integral one often employs discretizations. In the case of gravity and reparametrization-invariant systems, the latter of which we consider here as a toy example, discretizations generically break diffeomorphism and reparametrization symmetry, respectively. This has severe implications, as these symmetries determine the dynamics of the corresponding system. Indeed we will show that a discretized path integral with reparametrization-invariance is necessarily also discretization independent and therefore uniquely determined by the corresponding continuum quantum mechanical propagator. We use this insight to develop an iterative method for constructing such a discretized path integral, akin to a Wilsonian RG flow. This allows us to address the problem of discretization ambiguities and of an anomaly-free path integral measure for such systems. The latter is needed to obtain a path integral, that can act as a projector onto the physical states, satisfying the quantum constraints. We will comment on implications for discrete quantum gravity models, such as spin foams.