We analyze the properties of the tilted Szekeres spacetime, i.e. the version of such spacetime as seen by a congruence of observers with respect to which the fluid is moving. The imperfect fluid and the kinematical variables associated to the four-velocity of the fluid assigned by tilted observers are studied in detail. As it happens for the case of the Lemaitre-Tolman-Bondi spacetime, the fluid evolves nonreversibly (with nonvanishing entropy production) and is nongeodesic. However, unlike the latter case, the tilted observer detects vorticity in the congruence of the fluid world lines. Also, as for the nontilted congruence, the magnetic part of the Weyl tensor vanishes, reinforcing the nonradiative character of this kind of spacetime. Possible physical implications of these results are discussed.

A unique signature of the modified Newtonian dynamics (MOND) paradigm is its peculiar behavior in the vicinity of the points where the total Newtonian acceleration exactly cancels. In the Solar System, these are the saddle points of the gravitational potential near the planets. Typically, such points are embedded into low-acceleration bubbles where modified gravity theories à la MOND predict significant deviations from Newton’s laws. As it has been pointed out recently, the Earth-Sun bubble may be visited by the LISA Pathfinder spacecraft in the near future, providing a unique occasion to put these theories to a direct test. In this work, we present a high-precision model of the Solar System’s gravitational potential to determine accurate positions and motions of these saddle points and study the predicted dynamical anomalies within the framework of quasilinear MOND. Considering the expected sensitivity of the LISA Pathfinder probe, we argue that interpolation functions which exhibit a “faster” transition between the two dynamical regimes have a good chance of surviving a null result. An example of such a function is the QMOND analog of the so-called simple interpolating function which agrees well with much of the extragalactic phenomenology. We have also discovered that several of Saturn’s outermost satellites periodically intersect the Saturn-Sun bubble, providing the first example of Solar System objects that regularly undergo the MOND regime.

Quantum graphity offers the intriguing notion that space emerges in the low-energy states of the spatial degrees of freedom of a dynamical lattice. Here we investigate metastable domain structures which are likely to exist in the low-energy phase of lattice evolution. Through an annealing process we explore the formation of metastable defects at domain boundaries and the effects of domain structures on the propagation of bosons. We show that these structures should have observable background-independent consequences including scattering, double imaging, and gravitational lensing-like effects.

The reported spatial variation in the fine structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of $\alpha$. We show that while a single-wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding three parameters), a two-wall solution is a far better fit (despite adding three parameters over the single-wall solution). We derive a simple model accounting for the two domain wall solution. The goodness of these fits is, however, dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the standard model; however, the standard model itself is not a terrible fit to the data, having a $p$ value of $\sim 20\%$.

The properties of a helixlike shaped QCD string are studied in the context of the Lund fragmentation model, where the concept of a three-dimensional structure of the gluon field offers an alternative approach to the modeling of the transverse momentum of hadrons. The paper is focused on the phenomenology of the model, which introduces correlations between transverse and longitudinal components of hadrons, as well as azimuthal ordering of hadrons along the string. The similarities between 2-particle correlations stemming from the helix-string structure and those commonly attributed to the Bose-Einstein interference are pointed out. It is shown that the charged asymmetry observed in hadron production of close hadron pairs can be associated with fluctuations in the space-time history of the string breakup and with the presence of resonant hadronic states.

The present collider data put severe constraints on any type of new strongly interacting particle coupling to the Higgs boson. We analyze the phenomenological limits on exotic quarks belonging to nontriplet $SU(3{)}_C$ representations and their implications on Higgs searches. The discovery of the standard model Higgs, in the experimentally allowed mass range, would exclude the presence of exotic quarks coupling to it. Thus, such QCD particles could only exist provided that their masses do not originate in the SM Higgs mechanism.

We report a search for $B^0$ decays into invisible final states using a data sample of $657\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. The signal is identified by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring no other particles in the event. No significant signal is observed, and we obtain an upper limit of $1.3\times {10}^{-4}$ at the 90% confidence level for the branching fraction of invisible $B^0$ decay.

We present searches for the rare decay modes $D^0\to e^{+}{e}^{-}$, $D^0\to {\mu }^{+}{\mu }^{-}$, and $D^0\to e^{\pm }{\mu }^{\mp }$ in continuum $e^{+}{e}^{-}\to c\overline{c}$ events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of $468{\mathrm{fb}}^{-1}$. These decays are highly Glashow–Iliopoulos–Maiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the $D^0\to {\mu }^{+}{\mu }^{-}$ channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the Feldman–Cousins method, we set the following 90% confidence level intervals on the branching fractions: $\mathcal{B}(D^0\to e^{+}{e}^{-})<1.7\times {10}^{-7}$, $\mathcal{B}(D^0\to {\mu }^{+}{\mu }^{-})$ within $[0.6,8.1]\times {10}^{-7}$, and $\mathcal{B}(D^0\to e^{\pm }{\mu }^{\mp })<3.3\times {10}^{-7}$.

We perform a comparative theoretical study of the data at spacelike momentum transfer for the ${\gamma }^{*}\gamma \to {\pi }^0$ transition form factor, just reported by the Belle Collaboration, vs. those published before by BABAR, also including the older CLEO and CELLO data. Various implications for the structure of the ${\pi }^0$ distribution amplitude vis-à-vis those data are discussed and the existing theoretical predictions are classified into three distinct categories. We argue that the actual bifurcation of the data with antithetic trends is artificial and reason that the Belle data are the better option.

The eternally inflating multiverse provides a consistent framework to understand coincidences and fine-tuning in the Universe. As such, it provides the possibility of finding another coincidence: if the amount of slow-roll inflation in our past was only slightly more than the anthropic threshold, then spatial curvature might be measurable. We study this issue in detail, particularly focusing on the question: “If future observations reveal nonzero curvature, what can we conclude?” We find that whether an observable signal arises or not depends crucially on three issues: the cosmic history just before the observable inflation, the measure adopted to define probabilities in the eternally inflating spacetime, and the sign and strength of the correlation between the tunneling and slow-roll parts of the potential. We find that if future measurements find positive curvature at the level ${\Omega }_k\lesssim -{10}^{-4}$, then the framework of the eternally inflating multiverse, as currently understood, is excluded with high significance. If the measurements instead reveal negative curvature at the level ${\Omega }_k\gtrsim {10}^{-4}$, then we can conclude that (1) diffusive (new or chaotic type) eternal inflation did not occur in our immediate past; (2) our pocket universe was born by a bubble nucleation; (3) the probability measure does not reward volume increase; and (4) the origin of the observed slow-roll inflation is an accidental feature of the potential, presumably selected by anthropic conditions, and not due to a theoretical mechanism ensuring the flatness of the potential. Discovery of ${\Omega }_k\gtrsim {10}^{-4}$ would also give us nontrivial information about the correlation between the tunneling and slow-roll parts of the potential; for example, a strong correlation favoring large $N$ would be ruled out in certain measures. We also address the question of whether the current constraint on ${\Omega }_k$ is consistent with multiverse expectations; we find the answer to be yes, except that current observations, for many choices of measure, rule out the possibility of strong correlations in the potential which favor small values of $N$. In the course of this work we were led to consider vacuum decay branching ratios, and found that it is more likely than one might guess that the decays are dominated by a single channel. Planned future measurements of spatial curvature provide a valuable opportunity to explore the structure of the multiverse as well as the cosmic history just before the observable inflation.

Transient broadband noise in gravitational wave (GW) detectors—also known as noise triggers (referred to as triggers for brevity)—can often be a deterrant to the efficiency with which astrophysical search pipelines detect sources. It is important to understand their instrumental or environmental origin so that they could be eliminated or accounted for in the data. Since the number of triggers is large, data mining approaches such as clustering and classification are useful tools for this task. Classification of triggers based on a handful of discrete properties has been done in the past. A rich information content is available in the waveform or “shape” of the triggers that has had a rather restricted exploration so far. This paper presents a new way to classify triggers deriving information from both trigger waveforms as well as their discrete physical properties, using a sequential combination of the longest common subsequence (LCSS) and LCSS coupled with Fast Time Series Evaluation (FTSE) for waveform classification, and the multidimensional hierarchical classification (MHC) analysis for the grouping based on physical properties. A generalized $k$-means algorithm is used with the LCSS (and $\mathrm{LCSS}+\mathrm{FTSE}$) for clustering the triggers using a validity measure to determine the correct number of clusters in absence of any prior knowledge. The results have been demonstrated by simulations and by application to a segment of real LIGO data from the sixth science run.

We study the mass, the mixing, and the coupling with the $Z$ boson of the lightest Higgs boson in the next-to-minimal supersymmetric standard model with the ${\mathbb{Z}}_3$ symmetry. The vacuum structure of the Higgs potential is analyzed, and the new false vacua are discussed. The significant parameter region can be excluded by requiring the realistic vacuum to be deeper than false vacua. In numerical analysis, we also require the couplings to be perturbative up to the Grand Unified Theory scale. Our analysis results in constraints on the properties of the lightest Higgs boson.

We analyze topological charge contributions from classical $SU(2)$ center vortices with shapes of planes and spheres using different topological charge definitions, namely the center vortex picture of topological charge, a discrete version of $F\tilde{F}$ in the plaquette or hypercube definitions and the lattice index theorem. For the latter the zero modes of the Dirac operator in the fundamental and adjoint representations using both the overlap and asqtad staggered fermion formulations are investigated. We find several problems for the individual definitions and discuss the discrepancies between the different topological charge definitions. Our results show that the interpretation of topological charge in the background of center vortices is rather subtle.

We study a flavor-violating four-fermion interaction in the Lifshitz context, in $3+1$ dimensions and with a critical exponent $z=3$. This model is renormalizable, and features dynamical mass generation, as well as asymptotic freedom. At one-loop, it is only logarithmically divergent, but the superficial degree of divergence of the two-point functions is 3. We calculate the two-loop corrections to the propagators, and show that, at this order, the Lorentz-violating corrections to the IR dispersion relation are quadratic in the cut off. Furthermore, these corrections are too significant to represent a physical effect. As a consequence, the predictive power of the model in terms of Lorentz-violating effects in the propagation of particles is limited.

Cosmological magnetic fields in open Friedmann universes can experience superadiabatic amplification within the realm of conventional electromagnetism. This is possible mathematically, despite the conformal invariance of Maxwell’s equations, because Friedmann spacetimes with non-Euclidean spatial geometry are not globally conformal to Minkowski space. Physically, this means that even universes that are marginally open today can sustain large-scale magnetic fields that are substantially stronger than previously anticipated. In the present paper, we investigate this purely geometric amplification mechanism in greater detail, focusing on the early evolution of the electromagnetic modes in inflationary Friedmann models with hyperbolic spatial geometry. This also allows us to refine the earlier numerical estimates and provide the current spectrum of the residual, superadiabatically amplified magnetic field.

Many hadronic correlators used in spectroscopy calculations in lattice QCD simulations appear to show a log-normal distribution at intermediate time separations.

In this paper the properties of thermal Abelian monopoles in the deconfinement phase of the $SU(2)$ gluodynamics are considered. In particular, to study the properties of the Abelian monopole component of quark-gluon plasma (QGP), we calculate three-point correlation functions of monopoles for different temperatures from the region $T/T_c\in (1.5,6.8)$. The results of the calculation show that the three-point correlation functions can be described by independent pair correlations of monopoles. From this, one can conclude that the system of Abelian monopoles in QGP reveals the properties of a dilute gas. In addition, one can assert that the interaction between Abelian monopoles is a pair interaction and there are no three-particle forces acting between monopoles.

The light mesons such as $\pi$, $\rho$, $\omega$, $f_0$, and $a_0$ are possible candidates of magnetic degrees of freedom, if a magnetic dual picture of QCD exists. We construct a linear sigma model to describe spontaneous breaking of the magnetic gauge group, in which there is a stable vortex configuration of vector and scalar mesons. We numerically examine whether such a string can be interpreted as the confining string. By using meson masses and couplings as inputs, we calculate the tension of the string as well as the strength of the Coulomb force between static quarks. They are found to be consistent with those inferred from the quarkonium spectrum and the Regge trajectories of hadrons. By using the same Lagrangian, the critical temperature of the QCD phase transition is estimated, and a nontrivial flavor dependence is predicted. We also discuss a possible connection between the Seiberg duality and the magnetic model we studied.