We analyze a distinctive mechanism for inflation in which particle production slows down a scalar field on a steep potential and show how it descends from angular moduli in string compactifications. The analysis of density perturbations—taking into account the integrated effect of the produced particles and their quantum fluctuations—requires somewhat new techniques that we develop. We then determine the conditions for this effect to produce 60 e-foldings of inflation with the correct amplitude of density perturbations at the Gaussian level and show that these requirements can be straightforwardly satisfied. Finally, we estimate the amplitude of the non-Gaussianity in the power spectrum and find a significant equilateral contribution.

The Figure of Merit Science Working Group recently forecast the constraints on dark energy that will be achieved prior to the Joint Dark Energy Mission by ground-based experiments that exploit baryon acoustic oscillations, type Ia supernovae, and weak gravitational lensing. We show that cluster counts from ongoing and near-future surveys should provide robust, complementary dark energy constraints. In particular, we find that optimally combined optical and Sunyaev-Zel’dovich effect cluster surveys should improve the Dark Energy Task Force figure of merit for pre-Joint Dark Energy Mission projects by a factor of 2 even without prior knowledge of the nuisance parameters in the cluster mass-observable relation. Comparable improvements are achieved in the forecast precision of parameters specifying the principal component description of the dark energy equation of state parameter, as well as in the growth index $\gamma$. These results indicate that cluster counts can play an important complementary role in constraining dark energy and modified gravity even if the associated systematic errors are not strongly controlled.

Probabilities for observations in cosmology are conditioned both on the Universe’s quantum state and on local data specifying the observational situation. We show the quantum state defines a measure for prediction through such conditional probabilities that is well-behaved for spatially large or infinite universes when the probabilities that our data are replicated are taken into account. In histories where our data are rare volume weighting connects top-down probabilities conditioned on both the data and the quantum state to the bottom-up probabilities conditioned on the quantum state alone. We apply these principles to a calculation of the number of inflationary $e$-folds in a homogeneous, isotropic minisuperspace model with a single scalar field moving in a quadratic potential. We find that volume weighting is justified and the top-down probabilities favor a large number of $e$-folds, hereby predicting the curvature of our Universe at the present time to be approximately zero.

The $f(R)$ gravity theories provide an alternative way to explain the current cosmic acceleration without a dark energy matter component. If gravity is governed by a $f(R)$ theory, a number of issues should be reexamined in this framework, including the violation of causality problem on nonlocal scale. We examine the question as to whether the $f(R)$ gravity theories permit space-times in which the causality is violated. We show that the field equations of these $f(R)$ gravity theories do not exclude solutions with breakdown of causality for a physically well-motivated perfect-fluid matter content. We demonstrate that every perfect-fluid Gödel-type solution of a generic $f(R)$ gravity satisfying the condition $df/dR>0$ is necessarily isometric to the Gödel geometry, and therefore presents violation of causality. This result extends a theorem on Gödel-type models, which has been established in the context of general relativity. We also derive an expression for the critical radius $r_c$ (beyond which the causality is violated) for an arbitrary $f(R)$ theory, making apparent that the violation of causality depends on both the $f(R)$ gravity theory and the matter content. As an illustration, we concretely take a recent $f(R)$ gravity theory that is free from singularities of the Ricci scalar and is cosmologically viable, and show that this theory accommodates noncausal as well as causal Gödel-type solutions.

The generalized scalar-tensor models with Lagrangian $F(\varphi ,R)-U(\varphi )(\nabla \varphi {)}^2$ are considered. It is shown that the phantom-divide-line crossing and the deceleration to acceleration transition generally occur in these models. Two specific examples, the coupled quintessence model and the Brans-Dicke model, are considered. For the first example, it is shown that for the models with $\xi >3/16$, the $\omega =-1$ transition exists. This is verified numerically for some special cases. For the Brans-Dicke model, it is shown that the transition does not occur, a result which can be verified by using the exact solution of this model. Finally the contribution of quantum effects on these phenomena is investigated. It is shown that for some special cases where the $\omega =-1$ transition is classically forbidden, the quantum effects can induce transition. The $\xi =1/6$ of the coupled quintessence model is an example of this. The quantum effects are described via the account of conformal anomaly.

The accelerating expansion of the Universe at recent epochs has called into question the validity of general relativity on cosmological scales. One probe of gravity is a comparison of expansion history of the Universe with the history of structure growth via gravitational instability: general relativity predicts a specific relation between these two observables. Here we show that the mean pairwise streaming velocity of galaxy clusters provides a useful method of constraining this relation. Galaxy cluster velocities can be measured via the kinetic Sunyaev-Zeldovich distortion of the cosmic microwave background radiation. Future surveys can provide large enough catalogs of cluster velocities to discriminate between general relativity and other proposed gravitational theories.

We calculate the production rates of the second Kaluza-Klein (KK) photon ${\gamma }^{(2)}$ and $Z$ boson $Z^{(2)}$ at the LHC including all significant processes in the minimal universal extra dimension (MUED) model. For discrimination of the MUED model from other TeV scale models at the LHC, ${\gamma }^{(2)}$ and $Z^{(2)}$ play a crucial role. In order to discuss the discrimination and calculate their production rates, we derive KK number violating operators including the contribution of the top Yukawa coupling. Using these operators, we accurately calculate branching ratios of second KK particles. In addition we find that these KK number violating operators provide new processes for ${\gamma }^{(2)}$ and $Z^{(2)}$ productions, such as cascade decay from second KK quarks produced through these operators. They have large contributions to their total production rates. In particular, these production processes give the dominant contribution for ${\gamma }^{(2)}$ production for $1/R\gtrsim 800\mathrm{GeV}$. As a result, with an integrated luminosity of $100{\mathrm{fb}}^{-1}$, the number of produced ${\gamma }^{(2)}$ and $Z^{(2)}$ are estimated as ${10}^6–{10}^2$ for the compactification scale between 400 and 2000 GeV.

We present the Large Hadron Collider (LHC) discovery potential in the $Z^{\prime }$ and heavy neutrino sectors of a $U(1{)}_{B-L}$ enlarged standard model also encompassing 3 heavy Majorana neutrinos. This model exhibits novel signatures at the LHC, the most interesting arising from a $Z^{\prime }$ decay chain involving heavy neutrinos, eventually decaying into leptons and jets. In particular, this signature allows one to measure the $Z^{\prime }$ and heavy neutrino masses involved. In addition, over a large region of the parameter space, the heavy neutrinos are rather long-lived particles producing distinctive displaced vertices that can be seen in the detectors. Lastly, the simultaneous measurement of both the heavy neutrino mass and decay length enables an estimate of the absolute mass of the parent light neutrino.

The Randall-Sundrum model of warped geometry in a five-dimensional scenario, aimed at explaining the hierarchy between the Planck and electroweak scales, is intrinsically unstable in its minimal form due to negative tension of the visible brane. A proposed solution to the problem yields a negative cosmological constant in four dimensions. We show that this wrong-sign cosmological constant is restricted to small values, therefore requiring less cancellation from hitherto unknown physics, if bulk neutrinos are postulated to explain the observed neutrino mass pattern. Thus neutrino masses, a stable TeV-brane configuration and new physics in the context of the cosmological constant get rather suggestively connected by the same thread.

The distribution of the phase angle and the magnitude of the fermion determinant as well as its correlations with the baryon number and the chiral condensate are studied for QCD at non zero quark chemical potential. Results are derived to one-loop order in chiral perturbation theory. We find that the distribution of the phase angle is Gaussian for small chemical potential and a periodic Lorentzian when the quark mass is inside the support of the Dirac spectrum. The baryon number and chiral condensate are computed as a function of the phase of the fermion determinant and we discuss the severe cancellations which occur upon integration over the angle. We compute the distribution of the magnitude of the fermion determinant as well as the baryon number and chiral condensate at fixed magnitude. Finally, we consider QCD in one Euclidean dimension where it is shown analytically, starting from the fundamental QCD partition function, that the distribution of the phase of the fermion determinant is a periodic Lorentzian when the quark mass is inside the spectral density of the Dirac operator.

The approximate tree decays $B^{-}\to {\pi }^{-}{\pi }^0/{\rho }^{-}{\rho }^0$ may serve as benchmark channels for testing the various theoretical descriptions of the strong interaction dynamics in hadronic $B$ meson decays. The ratios of hadronic and differential semileptonic $B\to \pi \ell \nu /\rho \ell \nu$ decay rates at maximum recoil provide particularly clean probes of the QCD dynamics. We confront the recent next-to-next-to-leading order calculation in the QCD factorization framework with experimental data and find support for the factorization assumption. A detailed analysis of all tree-dominated $B\to \pi \pi /\pi \rho /\rho \rho$ decay modes seems to favor somewhat enhanced color-suppressed amplitudes, which may be accommodated in QCD factorization by a small value of the first inverse moment of the $B$ meson light-cone distribution amplitude, ${\lambda }_B\simeq 250\mathrm{MeV}$. Precise measurements of the semileptonic $B\to \rho \ell \nu$ spectrum could help to clarify this point.

The production of two weak bosons at the Large Hadron Collider will be one of the most important sources of standard model backgrounds for final states with multiple leptons. In this paper we consider several quantities that can help normalize the production of weak boson pairs. Ratios of inclusive cross sections for production of two weak bosons and Drell-Yan are investigated and the corresponding theoretical errors are evaluated. The possibility of predicting the jet veto survival probability of $VV$ production from Drell-Yan data is also considered. Overall, the theoretical errors on all quantities remain less than 5%–20%. The dependence of these quantities on the center of mass energy of the proton-proton collision is also studied.

An extension to the soft collinear effective theory description of hard jets is motivated to include the leading contributions between the propagating partons within the jet with partons radiated from a dense extended medium. The resulting effective Lagrangian, containing both a leading and a power suppressed (in the hard scale $Q^2$) contribution, arises primarily from interactions between the hard collinear modes in the jet with Glauber modes from the medium. In this first attempt, the interactions between the hard jet and soft and collinear partonic modes have been ignored, in an effort to focus solely on the interactions with the Glauber modes. While the effect of such modes on vacuum cross sections are suppressed by powers of the hard scale compared to the terms from the Lagrangian, such subleading contributions are enhanced by the extent of the medium and result in measurable corrections. The veracity of the derived Lagrangian is checked by direct comparison with known results from full QCD calculations of two physical observables: the transverse momentum broadening of hard jets in dense media and a reanalysis of the transverse momentum dependent parton distribution function.

We present a type-III version of inverse seesaw or, equivalently an inverse version of type-III seesaw. Naturally small neutrino masses arise at low-scale from the exchange of neutral fermions transforming as hyperchargeless $SU(2)$ triplets. In order to implement tribimaximal lepton mixing we supplement the minimal $SU(3)\times SU(2)\times U(1)$ gauge symmetry with an $A_4$-based flavor symmetry. Our scenario induces lepton flavor violating (LFV) $l_i\to l_j{\overline{l}}_k{l}_m$ decays that can proceed at the tree level, while radiative $l_i\to l_j\gamma$ decays and mu-e conversion in nuclei are also expected to be sizeable. LFV decays are related by the underlying flavor symmetry and the new fermions are also expected to be accessible for study at the LHC.

We report on a search for the process $p\overline{p}\to \gamma +W/Z$ with $W/Z\to q\overline{q}$ in events containing two jets and a photon at the center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$, using $184{\mathrm{pb}}^{-1}$ of data collected by the CDF II detector. A neural network event selection has been developed to optimize the rejection of the large QCD production background; it is shown that this method gives a significant improvement in both signal-to-noise ratio and signal sensitivity, as compared with an event selection based on conventional cuts. An upper limit is presented for the $\gamma +W/Z$ production cross section with the $W$ and $Z$ decaying hadronically.

The ZEPLIN-III experiment in the Palmer Underground Laboratory at Boulby uses a 12 kg two-phase xenon time-projection chamber to search for the weakly interacting massive particles (WIMPs) that may account for the dark matter of our Galaxy. The detector measures both scintillation and ionization produced by radiation interacting in the liquid to differentiate between the nuclear recoils expected from WIMPs and the electron-recoil background signals down to $\sim 10\mathrm{keV}$ nuclear-recoil energy. An analysis of $847\mathrm{kg}·\mathrm{days}$ of data acquired between February 27, 2008, and May 20, 2008, has excluded a WIMP-nucleon elastic scattering spin-independent cross section above $8.1\times {10}^{-8}\mathrm{pb}$ at $60\mathrm{GeV}{c}^{-2}$ with a 90% confidence limit. It has also demonstrated that the two-phase xenon technique is capable of better discrimination between electron and nuclear recoils at low-energy than previously achieved by other xenon-based experiments.

We present a generic method for improving the effectiveness of heavy particle searches in hadronic channels at the Large Hadron Collider. By selectively removing, or pruning, protojets from the substructure provided by a $k_T$-type jet algorithm, we improve the mass resolution for heavy decays and decrease the QCD background. We show that the protojets removed are typical of soft radiation and underlying event contributions, and atypical of accurately reconstructed heavy particles.

We obtain the leading derivative corrections to an expression for the Seiberg-Witten map given by Banerjee and Yang and show how they affect the noncommutative deformation of the Maxwell action, as well as the matter coupling in noncommutative emergent gravity.

We generalize (linearized) relativistic hydrodynamics by including all order gradient expansion of the energy-momentum tensor, parametrized by four momenta-dependent transport coefficients, one of which is the usual shear viscosity. We then apply the AdS/CFT duality for $\mathcal{N}=4$ SUSY in order to compute the retarded correlators of the energy-momentum tensor. From these correlators we determine a large set of transport coefficients of third- and fourth-order hydrodynamics. We find that higher order terms have a tendency to reduce the effect of viscosity.

Some spontaneously broken gauge theories with unbroken non-Abelian gauge groups contain massless magnetic monopoles that are realized classically as clouds of non-Abelian field surrounding one or more massive monopoles. We use moduli space methods to investigate the properties of these massless monopole clouds. We show that the natural metric on the Nahm data for a class of $\mathrm{SU}(2M+2)$ solutions with $2M$ massive and $M(2M-1)$ massless monopoles can be obtained from that for a simpler class of $\mathrm{SU}(M+1)$ solutions. For the $M=1$ case, we show that the Nahm data metric is isomorphic to the metric for the moduli of the BPS solutions, thus verifying a previously conjectured result. For $M=2$ we use our results and the moduli space approximation to obtain an effective Lagrangian for an axially symmetric class of solutions. Using this Lagrangian, we study the interactions between the two types of clouds that appear. We show that, although the static spacetime field configurations suggest that the clouds might be rather diffuse, in scattering processes they behave as if they were relatively thin hard shells.