In the framework of supersymmetric grand unified theories, the minimal Higgs sector is often extended by introducing multidimensional Higgs representations in order to obtain realistic models. However these constructions should remain anomaly-free, which significantly constrains their structure. We review the necessary conditions for the cancellation of anomalies in general and discuss in detail the different possibilities for supersymmetric SU(5) models. Alternative anomaly-free combinations of Higgs representations, beyond the usual vectorlike choice, are identified, and it is shown that their corresponding $\beta$ functions are not equivalent. Although the unification of gauge couplings is not affected, the introduction of multidimensional representations leads to different scenarios for the perturbative validity of the theory up to the Planck scale.

In the context of a microscopic model of string-inspired foam, in which foamy structures are provided by brany pointlike defects (D-particles) in space-time, we discuss flavor mixing as a result of flavor nonpreserving interactions of (low-energy) fermionic stringy matter excitations with the defects. Such interactions involve splitting and capture of the matter string state by the defect, and subsequent re-emission. As a result of charge conservation, only electrically neutral matter can interact with the D-particles. Quantum fluctuations of the D-particles induce a nontrivial space-time background; in some circumstances, this could be akin to a cosmological Friedman-Robertson-Walker expanding-universe, with weak (but nonzero) particle production. Furthermore, the D-particle medium can induce an Mikheyev-Smirnov-Wolfenstein-type effect. We have argued previously, in the context of bosons, that the so-called flavor vacuum is the appropriate state to be used, at least for low-energy excitations, with energies/momenta up to a dynamically determined cutoff scale. Given the intriguing mass scale provided by neutrino flavor mass differences from the point of view of dark energy, we evaluate the flavor-vacuum expectation value (condensate) of the stress-energy tensor of the $1/2$-spin fields with mixing in an effective-low-energy quantum field theory in this foam-induced curved space-time. We demonstrate, at late epochs of the Universe, that the fermionic vacuum condensate behaves as a fluid with negative pressure and positive energy; however, the equation of state has $w_{\mathrm{fermion}}>-1/3$ and so the contribution of the fermion-fluid flavor vacuum alone could not yield accelerating universes. Such contributions to the vacuum energy should be considered as (algebraically) additive to the flavored boson contributions, evaluated in our previous works; this should be considered as natural from (broken) target-space supersymmetry that characterizes realistic superstring/supermembrane models of space-time foam. The boson fluid is also characterized by positive energy and negative pressure, but its equation of state is, for late eras, close to $w_{\mathrm{boson}}\to -1$, and hence overall the D-foam universe appears accelerating at late eras.

We analyze the phase space of gravity nonminimally coupled to a scalar field in a generic local Lorentz frame. We reduce the set of constraints to a first class one by fixing a specific hypersurfaces in the phase space. The main issue of our analysis is to extend the features of the vacuum case to the presence of scalar matter by recovering the emergence of an SU(2) gauge structure and the nondynamical role of boost variables. Within this scheme, the supermomentum and the super-Hamiltonian are those ones associated with a scalar field minimally coupled to the metric in the Einstein frame. Hence, the kinematical Hilbert space is defined as in canonical loop quantum gravity with a scalar field, but the differences in the area spectrum are outlined to be the same as in the time-gauge approach.

We study the growth of matter density perturbations ${\delta }_m$ for a number of viable $f(R)$ gravity models that satisfy both cosmological and local gravity constraints, where the Lagrangian density $f$ is a function of the Ricci scalar $R$. If the parameter $m\equiv R{f}_{,RR}/f_{,R}$ today is larger than the order of ${10}^{-6}$, linear perturbations relevant to the matter power spectrum evolve with a growth rate $s\equiv d\ln {\delta }_m/d\ln a$ ($a$ is the scale factor) that is larger than in the $\Lambda \mathrm{CDM}$ model. We find the window in the free parameter space of our models for which spatial dispersion of the growth index ${\gamma }_0\equiv \gamma (z=0)$ ($z$ is the redshift) appears in the range of values $0.40\lesssim {\gamma }_0\lesssim 0.55$, as well as the region in parameter space for which there is essentially no dispersion and ${\gamma }_0$ converges to values around $0.40\lesssim {\gamma }_0\lesssim 0.43$. These latter values are much lower than in the $\Lambda \mathrm{CDM}$ model. We show that these unusual dispersed or converged spectra are present in most of the viable $f(R)$ models with $m(z=0)$ larger than the order of ${10}^{-6}$. These properties will be essential in the quest for $f(R)$ modified gravity models using future high-precision observations and they confirm the possibility to distinguish clearly most of these models from the $\Lambda \mathrm{CDM}$ model.

The two-body dynamics in general relativity has been solved perturbatively using the post-Newtonian (PN) approximation. The evolution of the orbital phase and the emitted gravitational radiation are now known to a rather high order up to $\mathcal{O}(v^8)$, $v$ being the characteristic velocity of the binary. The orbital evolution, however, cannot be specified uniquely due to the inherent freedom in the choice of parameter used in the PN expansion, as well as the method pursued in solving the relevant differential equations. The goal of this paper is to determine the (dis)agreement between different PN waveform families in the context of initial and advanced gravitational-wave detectors. The waveforms employed in our analysis are those that are currently used by Initial LIGO/Virgo, that is, the time-domain PN models TaylorT1, TaylorT2, TaylorT3, the Fourier-domain representation TaylorF2 (or stationary phase approximant), and the effective-one-body model, and two more recent models, TaylorT4 and TaylorEt. For these models we examine their overlaps with one another for a number of different binaries at 2PN, 3PN, and 3.5PN orders to quantify their differences. We then study the overlaps of these families with the prototype effective-one-body family, currently used by Initial LIGO, calibrated to numerical-relativity simulations to help us decide whether there exist preferred families, in terms of detectability and computational cost, that are the most appropriate as search templates. We conclude that as long as the total mass remains less than a certain upper limit $M_{\mathrm{crit}}$, all template families at 3.5PN order (except TaylorT3 and TaylorEt) are equally good for the purpose of detection. The value of $M_{\mathrm{crit}}$ is found to be $\sim 12M_{\odot }$ for Initial, Enhanced, and Advanced LIGO. From a purely computational point of view, we recommend that 3.5PN TaylorF2 be used below $M_{\mathrm{crit}}$ and that the effective-one-body model calibrated to numerical-relativity simulations be used for total binary mass $M>M_{\mathrm{crit}}$.

With the puncture method for black hole simulations, the second infinity of a wormhole geometry is compactified to a single “puncture point” on the computational grid. The region surrounding the puncture quickly evolves to a trumpet geometry. The computational grid covers only a portion of the trumpet throat. It ends at a boundary whose location depends on resolution. This raises the possibility that perturbations in the trumpet geometry could propagate down the trumpet throat, reflect from the puncture boundary, and return to the black hole exterior with a resolution-dependent time delay. Such pathological behavior is not observed. This is explained by the observation that some perturbative modes propagate in the conformal geometry, others propagate in the physical geometry. The puncture boundary exists only in the physical geometry. The modes that propagate in the physical geometry are always directed away from the computational domain at the puncture boundary. The finite difference stencils ensure that these modes are advected through the boundary with no coupling to the modes that propagate in the conformal geometry. These results are supported by numerical experiments with a code that evolves spherically symmetric gravitational fields with standard Cartesian finite difference stencils. The code uses the Baumgarte-Shapiro-Shibata-Nakamura formulation of Einstein’s equations with $1+\log $ slicing and gamma-driver shift conditions.

The stability of isotropic cosmological solutions in the Bianchi I model is considered. We prove that the stability of isotropic solutions in the Bianchi I metric for a positive Hubble parameter follows from their stability in the Friedmann-Robertson-Walker metric. This result is applied to models inspired by string field theory, which violate the null energy condition. Examples of stable isotropic solutions are presented. We also consider the $k$-essence model and analyze the stability of solutions of the form $\Phi (t)=t$.

Does a future observation of low energy leptonic $CP$ violation imply a lepton asymmetry both in flavored leptogenesis and in its one-flavor approximation? Under reasonable assumptions this is the case if lepton masses and mixings are explained by a flavor symmetry in a seesaw model. We are particularly interested in the class of flavor theory which leads to $U_{e3}=0$ at leading order. We explicitly implement this approach with a predictive seesaw model for tribimaximal mixing (TBM) and show how cosmological baryon asymmetry can be directly triggered by low energy phases appearing in $U_{e3}$. In this model, thanks to this direct correlation, we can derive a lower bound on the reactor angle ${\theta }_{13}$: ${sin}^2{\theta }_{13}\gtrsim 0.005$.

The standard model Higgs boson can serve as the inflaton field of slow roll inflationary models provided it exhibits a large nonminimal coupling with the gravitational scalar curvature. The Higgs boson self interactions and its couplings with a standard model singlet scalar serving as the source of dark matter are then subject to cosmological constraints. These bounds, which can be more stringent than those arising from vacuum stability and perturbative triviality alone, still allow values for the Higgs boson mass which should be accessible at the LHC. As the Higgs boson coupling to the dark matter strengthens, lower values of the Higgs boson mass consistent with the cosmological data are allowed.

We explore aspects of the phase structure of $SU(2)$ and $SU(3)$ lattice gauge theories at strong coupling with many flavors $N_f$ of Wilson fermions in the fundamental representation. The pseudoscalar meson mass as a function of hopping parameter is observed to deviate from the expected analytic dependence, at least for sufficiently large $N_f$. Implications of this effect are discussed, including the relevance to recent searches for an infrared fixed point.

We present next-to-leading order QCD predictions for a variety of distributions in $W+3$-jet production at both the Tevatron and the Large Hadron Collider. We include all subprocesses and incorporate the decay of the $W$ boson into leptons. Our results are in excellent agreement with existing Tevatron data and provide the first quantitatively precise next-to-leading order predictions for the LHC. We include all terms in an expansion in the number of colors, confirming that the specific leading-color approximation used in our previous study is accurate to within 3%. The dependence of the cross section on renormalization and factorization scales is reduced significantly with respect to a leading-order calculation. We study different dynamical scale choices, and find that the total transverse energy is significantly better than choices used in previous phenomenological studies. We compute the one-loop matrix elements using on-shell methods, as numerically implemented in the BlackHat code. The remaining parts of the calculation, including generation of the real-emission contributions and integration over phase space, are handled by the SHERPA package.

We discuss the phase structure of quantum chromodynamics (QCD) with two colors and two flavors of light quarks. This is motivated by the increasing interest in the QCD phase diagram as follows: (1) The QCD critical point search has been under intensive dispute and its location and existence suffer from uncertainty of effective $\mathrm{U}(1{)}_{\mathrm{A}}$ symmetry restoration. (2) A new phase called quarkyonic matter is drawing theoretical and experimental attention but it is not clear whether it can coexist with diquark condensation. We point out that two-color QCD is nontrivial enough to contain essential ingredients for (1) and (2) both, and most importantly, is a system without the sign problem in numerical simulations on the lattice. We adopt the two-flavor Nambu–Jona-Lasinio model extended with the two-color Polyakov loop and make quantitative predictions that can be tested by lattice simulations.

We study the possibility to test the type I seesaw mechanism for neutrino masses at the CERN Large Hadron Collider. The inclusion of three generations of right-handed neutrinos ($N_i$) provides an attractive option of gauging the $B-L$ accidental symmetry in the standard model (as well as an extended symmetry $X=Y-5(B-L)/4$). The production mechanisms for the right-handed neutrinos through the $Z^{\prime }$ gauge boson in the $U(1{)}_{B-L}$ and $U(1{)}_X$ extensions of the standard model are studied. We discuss the flavor combinations of the charged leptons from the decays of $N_i$ in the $\Delta L=2$ channels. We find that the clean channels with dilepton plus jets and possible secondary vertices of the $N$ decay could provide conclusive signals at the LHC in connection with the hierarchical pattern of the light neutrino masses and mixing properties within the type I seesaw mechanism.

We have developed an efficient simulation algorithm for strongly interacting relativistic fermions in two-dimensional field theories based on a formulation as a loop gas. It essentially eliminates critical slowing down by sampling two-point correlation functions and allows simulations directly in the massless limit at the critical point. It generates loop configurations with fluctuating topological boundary conditions enabling one to simulate fermions with arbitrary periodic or antiperiodic boundary conditions. As illustrative examples, the algorithm is applied to the Gross-Neveu model and to the Schwinger model in the strong coupling limit.

We measure the rate of $D^0\mathrm{\text{−}}{\overline{D}}^0$ mixing with the observable $y_{CP}=({\tau }_{K\pi }/{\tau }_{KK})-1$, where ${\tau }_{KK}$ and ${\tau }_{K\pi }$ are, respectively, the mean lifetimes of $CP$-even $D^0\to K^{+}{K}^{-}$ and $CP$-mixed $D^0\to K^{-}{\pi }^{+}$ decays, using a data sample of $384{\mathrm{fb}}^{-1}$ collected by the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ Factory. From a sample of $D^0$ and ${\overline{D}}^0$ decays where the initial flavor of the decaying meson is not determined, we obtain $y_{CP}=[1.12\pm 0.26(\mathrm{stat})\pm 0.22(\mathrm{syst})]\%$, which excludes the no-mixing hypothesis at $3.3\sigma$, including both statistical and systematic uncertainties. This result is in good agreement with a previous BABAR measurement of $y_{CP}$ obtained from a sample of $D^{*+}\to D^0{\pi }^{+}$ events, where the $D^0$ decays to $K^{-}{\pi }^{+}$, $K^{+}{K}^{-}$, and ${\pi }^{+}{\pi }^{-}$, which is disjoint with the untagged $D^0$ events used here. Combining the two results taking into account statistical and systematic uncertainties, where the systematic uncertainties are assumed to be 100% correlated, we find $y_{CP}=[1.16\pm 0.22(\mathrm{stat})\pm 0.18(\mathrm{syst})]\%$, which excludes the no-mixing hypothesis at $4.1\sigma$.

It is argued that the tetrad in a recent paper by Porto and Rothstein on gravitational spin-spin coupling should not have the given form. The fixation of that tetrad was suggested by Steinhoff, Hergt, and Schäfer as a possible source for the disagreement found in the spin-squared dynamics. However, this inconsistency will only show up in the next-to-leading order spin-orbit dynamics and not in the spin-squared dynamics. Instead, the disagreement found at the next-to-leading order spin-squared level is due to a sign typo in the spin-squared paper by Porto and Rothstein.

While the number of metastable landscape vacua in string theory is vast, the number of supermoduli vacua which lead to distinct low-energy physics is even larger, perhaps infinitely so. From the anthropic perspective it is therefore important to understand whether complex life is possible on moduli space—i.e., in low-energy effective theories with (1) exact supersymmetry and (2) some massless multiplets (moduli). Unless life is essentially impossible on moduli space as a consequence of these characteristics, anthropic reasoning in string theory suggests that the overwhelming majority of sentient beings would observe 1–2. We investigate whether 1 and 2 are by themselves automatically inimical to life and conclude, tentatively, that they are not. In particular, we describe moduli scenarios in which complex life seems possible.

The Galilean conformal algebra has recently been realized in the study of the nonrelativistic limit of the AdS/CFT conjecture. This was obtained by a systematic parametric group contraction of the parent relativistic conformal field theory. In this paper, we extend the analysis to include supersymmetry. We work at the level of the coordinates in superspace to construct the $N=1$ super-Galilean conformal algebra. One of the interesting outcomes of the analysis is that one is able to naturally extend the finite algebra to an infinite one. This looks structurally similar to the $N=1$ superconformal algebra in two dimensions, but is different. We also comment on the extension of our construction to cases of higher $N$.

We extend the lightcone worldsheet lattice approach to string theory, proposed in 1977 by Giles and me, to allow for coincident D-branes. We find a convenient lattice representation of Dirichlet boundary conditions, which the open string coordinates transverse to the D-branes satisfy. We then represent the sum over all planar open string multiloop diagrams by introducing an Ising spin system on the worldsheet lattice to keep track of the presence or absence of fluctuating boundaries. Finally we discuss a simple mean field treatment of the resulting coupled Ising/coordinate worldsheet system. The interplay between Neumann and Dirichlet boundary conditions leads to a richer phase structure, within this mean field approximation, than that found by Orland for the original system with only Neumann conditions.

In this work, we examine the finite temperature properties of the $CPT$-even and Lorentz-invariance-violating (LIV) electrodynamics of the standard model extension, represented by the term $W_{\alpha \nu \rho \phi }{F}^{\alpha \nu }{F}^{\rho \phi }$. We begin analyzing the Hamiltonian structure following the Dirac’s procedure for constrained systems and construct a well-defined and gauge invariant partition function in the functional integral formalism. Next, we specialize for the nonbirefringent coefficients of the tensor $W_{\alpha \nu \rho \phi }$. In the sequel, the partition function is explicitly carried out for the parity-even sector of the tensor $W_{\alpha \nu \rho \phi }$. The modified partition function is a power of the Maxwell’s partition function. It is observed that the LIV coefficients induce an anisotropy in the black body angular energy density distribution. The Planck’s radiation law, however, retains its frequency dependence and the Stefan-Boltzmann law keeps the usual form, except for a change in the Stefan-Boltzmann constant by a factor containing the LIV contributions.