The eta problem is one of the most significant obstacles to building a successful inflationary model in string theory. Planck mass suppressed corrections to the inflaton potential generally lead to inflaton masses of order the Hubble scale and generate contributions of order unity to the $\eta$ slow-roll parameter rendering prolonged slow-roll inflation impossible. We demonstrate the severity of this problem in the context of brane antibrane inflation in a warped throat of a Calabi-Yau flux compactification with all phenomenologically dangerous moduli stabilized. Using numerical solutions we show that the eta problem can be avoided in scenarios where the inflaton is nonminimally coupled to gravity and has Dirac-Born-Infeld kinetic term. We show that the resulting cosmic microwave background observables such as measures of non-Gaussianites can, in principle, serve as a probe of scalar-gravity couplings.

We compute the leading order connected four-point function of the primordial curvature perturbation coming from the four-point function of the fields in multifield DBI-inflation models. We confirm that the consistency relations in the squeezed limit and in the counter-collinear limit hold as in single-field models thanks to special properties of the DBI action. We also study the momentum dependence of the trispectra coming from the adiabatic, mixed and purely entropic contributions separately and we find that they have different momentum dependence. This means that if the amount of the transfer from the entropy perturbations to the curvature perturbation is significantly large, the trispectrum can distinguish multifield DBI-inflation models from single-field DBI-inflation models. A large amount of transfer $T_{\mathcal{R}\mathcal{S}}\gg 1$ suppresses the tensor-to-scalar ratio $r\propto T_{\mathcal{R}\mathcal{S}}^{-2}$ and the amplitude of the bispectrum $f_{\mathrm{NL}}^{\mathrm{equi}}\propto T_{\mathcal{R}\mathcal{S}}^{-2}$ and so it can ease the severe observational constraints on the DBI-inflation model based on string theory. On the other hand, it enhances the amplitude of the trispectrum ${\tau }_{\mathrm{NL}}^{\mathrm{equi}}\propto T_{\mathcal{R}\mathcal{S}}^2{f}_{\mathrm{NL}}^{\mathrm{equi}2}$ for a given amplitude of the bispectrum.

Numerous experimental anomalies hint at the existence of a dark matter (DM) multiplet ${\chi }_i$ with small mass splittings. We survey the simplest such models which arise from DM in the low representations of a new SU(2) gauge symmetry, whose gauge bosons have a small mass $\mu \lesssim 1\mathrm{GeV}$. We identify preferred parameters $M_{\chi }\cong 1\mathrm{TeV}$, $\mu \sim 100\mathrm{MeV}$, ${\alpha }_g\sim 0.04$, and the $\chi \chi \to 4e$ annihilation channel, for explaining PAMELA, Fermi, and INTEGRAL/SPI lepton excesses, while remaining consistent with constraints from relic density, diffuse gamma rays, and the CMB. This consistency is strengthened if DM annihilations occur mainly in subhalos, while excitations (relevant to the excited DM proposal to explain the 511 keV excess) occur in the galactic center, due to higher velocity dispersions in the galactic center, induced by baryons. We derive new constraints and predictions which are generic to these models. Notably, decays of excited DM states ${\chi }^{\prime }\to \chi \gamma$ arise at one loop and could provide a new signal for INTEGRAL/SPI; big bang nucleosynthesis constraints on the density of dark SU(2) gauge bosons imply a lower bound on the mixing parameter $ϵ$ between the SU(2) gauge bosons and photon. These considerations rule out the possibility of the gauge bosons that decay into $e^{+}{e}^{-}$ being long-lived. We study in detail models of doublet, triplet, and quintuplet DM, showing that both normal and inverted mass hierarchies can occur, with mass splittings that can be parametrically smaller [e.g., $O(100)\mathrm{keV}$] than the generic MeV scale of splittings. A systematic treatment of $Z_2$ symmetry, which insures the stability of the intermediate DM state, is given for cases with inverted mass hierarchy, of interest for boosting the 511 keV signal from the excited dark matter mechanism.

In this work, we explore the cosmological consequences of the recently released Constitution sample of 397 Type Ia supernovae (SNIa). By revisiting the Chevallier-Polarski-Linder (CPL) parametrization, we find that, for fitting the Constitution set alone, the behavior of dark energy (DE) significantly deviates from the cosmological constant $\Lambda$, where the equation of state (EOS) $w$ and the energy density ${\rho }_{\Lambda }$ of DE will rapidly decrease along with the increase of redshift $z$. Inspired by this clue, we separate the redshifts into different bins, and discuss the models of a constant $w$ or a constant ${\rho }_{\Lambda }$ in each bin, respectively. It is found that for fitting the Constitution set alone, $w$ and ${\rho }_{\Lambda }$ will also rapidly decrease along with the increase of $z$, which is consistent with the result of CPL model. Moreover, a step function model in which ${\rho }_{\Lambda }$ rapidly decreases at redshift $z\sim 0.331$ presents a significant improvement ($\Delta {\chi }^2=-4.361$) over the CPL parametrization, and performs better than other DE models. We also plot the error bars of DE density of this model, and find that this model deviates from the cosmological constant $\Lambda$ at 68.3% confidence level (CL); this may arise from some biasing systematic errors in the handling of SNIa data, or more interestingly from the nature of DE itself. In addition, for models with same number of redshift bins, a piecewise constant ${\rho }_{\Lambda }$ model always performs better than a piecewise constant $w$ model; this shows the advantage of using ${\rho }_{\Lambda }$, instead of $w$, to probe the variation of DE.

We present a general relativistic description of galaxy clustering in a Friedmann-Lemaître-Robertson-Walker universe. The observed redshift and position of galaxies are affected by the matter fluctuations and the gravity waves between the source galaxies and the observer, and the volume element constructed by using the observables differs from the physical volume occupied by the observed galaxies. Therefore, the observed galaxy fluctuation field contains additional contributions arising from the distortion in observable quantities and these include tensor contributions as well as numerous scalar contributions. We generalize the linear bias approximation to relate the observed galaxy fluctuation field to the underlying matter distribution in a gauge-invariant way. Our full formalism is essential for the consistency of theoretical predictions. As our first application, we compute the angular auto correlation of large-scale structure and its cross correlation with CMB temperature anisotropies. We comment on the possibility of detecting primordial gravity waves using galaxy clustering and discuss further applications of our formalism.

The evolution of scalar linear perturbations is studied in gauge-invariant approach for 2-component models with nonrelativistic matter and minimally coupled scalar fields, the potentials of which were constructed for either constant dark energy equation of state parameter $w$ or its adiabatic sound speed $c_a^2$ equal to zero. The numerical solutions show that such fields are almost smoothed out on subhorizon scales. However, they cause the scale dependent suppression of the nonrelativistic matter density perturbations and the decay of gravitational potential, which can be used for choice of the dark energy model. We discuss two types of the Lagrangian: classical and tachyonic ones. As our results show, the fields with $w=\mathrm{const}$ are almost indistinguishable, while for fields with $c_a^2=0$ the difference of dark energy effective sound speeds $c_s^2$, which is caused by the shape of Lagrangian, affects the evolution of perturbations significantly. We present also the transfer functions for both components.

We give the first demonstration of unitarity violation in the sequential neutrino mixing matrix in a scenario with extra compact spacelike dimensions. Gauge singlet neutrinos are assumed to propagate in one extra dimension, giving rise to an infinite tower of states in the effective four-dimensional theory. It is shown that this leads to small lepton-number violating entries in the neutrino mass matrix, which can violate unitarity on the order of 1%.

When a top quark decays there is a large amount of angular correlation, in its rest frame, between its spin orientation and the direction of flight of the charged lepton from its decay. In this paper we investigate the prospects of measuring this angular correlation using the MC@NLO framework. The strength of the correlation is investigated for different spin bases. The robustness against variation of parton distribution function sets and uncertainties, factorization scale dependence, center-of-mass energy, and the jet $R$-parameter is also examined.

We present an economic model that establishes a link between neutrino masses and properties of the dark matter candidate. The particle content of the model can be divided into two groups: light particles with masses lighter than the electroweak scale and heavy particles. The light particles, which also include the dark matter candidate, are predicted to show up in the low energy experiments such as ($K\to l+\mathrm{\text{missing energy}}$), making the model testable. The heavy sector can show up at the LHC and may give rise to $\mathrm{Br}(l_i\to l_j\gamma )$ close to the present bounds. In principle, the new couplings of the model can independently be derived from the data from the LHC and from the information on neutrino masses and lepton flavor violating rare decays, providing the possibility of an intensive cross-check of the model.

We have studied the prospects of measuring the $CP$ violating phase with atmospheric neutrinos at a large magnetized iron calorimeter detector considering the muons (directly measurable) of the neutrino events generated by a Monte Carlo event generator Nuance. The effect of ${\theta }_{13}$ and ${\delta }_{CP}$ appears dominantly neither in atmospheric neutrino oscillation nor in solar neutrino oscillation, but appears as subleading in both cases. These are observable in the range of $E\sim 1\mathrm{GeV}$ for atmospheric neutrino, where solar and atmospheric oscillation couple. In this regime, the quasielastic events dominate and the energy resolution is very good, but the angular resolution is very poor. Unlike beam experiments this poor angular resolution acts against its measurements. However, we find that one can be able to distinguish ${\delta }_{CP}\approx 0°$ and 180° at 90% confidence level. We find no significant sensitivity for ${\delta }_{CP}\approx 90°$ or 270°.

A resonantly enhanced photon-regeneration experiment to search for the axion or axionlike particles is described. This experiment is a shining light through walls study, where photons traveling through a strong magnetic field are (in part) converted to axions; the axions can pass through an opaque wall and convert (in part) back to photons in a second region of strong magnetic field. The photon regeneration is enhanced by employing matched Fabry-Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon-regeneration magnet. Compared to simple single-pass photon regeneration, this technique would result in a gain of $(\mathcal{F}/\pi {)}^2$, where $\mathcal{F}$ is the finesse of each cavity. This gain could feasibly be as high as ${10}^{10}$, corresponding to an improvement in the sensitivity to the axion-photon coupling, $g_{a\gamma \gamma }$, of order $(\mathcal{F}/\pi {)}^{1/2}\sim 300$. This improvement would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar axion searches. This report gives a detailed discussion of the scheme for actively controlling the two Fabry-Perot cavities and the laser frequencies, and describes the heterodyne signal detection system, with limits ultimately imposed by shot noise.

We propose a new mechanism for generating small neutrino masses which predicts the relation $m_{\nu }\sim v^4/M^3$, where $v$ is the electroweak scale, rather than the conventional seesaw formula $m_{\nu }\sim v^2/M$. Such a mass relation is obtained via effective dimension seven operators $LLHH(H^{†}H)/M^3$, which arise when an isospin $3/2$ Higgs multiplet $\Phi$ is introduced along with isotriplet leptons. The masses of these particles are naturally in the TeV scale. The triply charged Higgs boson contained in $\Phi$ can be pair produced at the LHC and the Tevatron, with ${\Phi }^{+++}$ decaying into $W^{+}{\ell }^{+}{\ell }^{+}$ or $W^{+}{W}^{+}{W}^{+}$, possibly with displaced vertices. The leptonic decays of ${\Phi }^{+++}$ will help discriminate between normal and inverted hierarchies of neutrino masses. This scenario also allows for raising the standard Higgs boson mass to values in excess of 500 GeV.

We study $D$-dimensional gauge theory with an extra dimension of a circle at finite temperature. We mainly focus on the expectation value of the gauge field for the direction of the extra dimension, which is the order parameter of the gauge symmetry breaking. We evaluate the effective potential in the one-loop approximation at finite temperature. We show that the vacuum configuration of the theory at finite temperature is determined by a ($D-1$)-dimensional gauge theory defined by removing the Euclidean time coordinate as well as all of the fermions from the original $D$-dimensional gauge theory on the circle. It is pointed out that gauge symmetry nonrestoration and/or inverse symmetry breaking can occur at high temperature in a class of gauge theories on circles and that phase transitions (if they occur) are, in general, expected to be first order.

We calculate the free energy of a hot gas of electrons and photons to three loops using the hard-thermal-loop perturbation theory reorganization of finite-temperature perturbation theory. We calculate the free energy through three loops by expanding in a power series in $m_D/T$, $m_f/T$, and $e^2$, where $m_D$ and $m_f$ are thermal masses and $e$ is the coupling constant. We demonstrate that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling, $e\sim 2$. The reorganization is gauge invariant by construction, and due to cancellation among various contributions, we obtain a completely analytic result for the resummed thermodynamic potential at three loops. Finally, we compare our result with similar calculations that use the $\Phi$-derivable approach.

A new gauge driver is introduced for the generalized harmonic (GH) representation of Einstein’s equation. This new driver allows a rather general class of gauge conditions to be implemented in a way that maintains the hyperbolicity of the combined evolution system. This driver is more stable and effective and, unlike previous drivers, allows stable evolutions using the dual-frame evolution technique. Appropriate boundary conditions for this new gauge driver are constructed, and a new boundary condition for the “gauge” components of the spacetime metric in the GH Einstein system is introduced. The stability and effectiveness of this new gauge driver are demonstrated through numerical tests, which impose a new damped-wave gauge condition on the evolutions of single black-hole spacetimes.

In Newtonian gravitational theory, a tidal Love number relates the mass multipole moment created by tidal forces on a spherical body to the applied tidal field. The Love number is dimensionless, and it encodes information about the body’s internal structure. We present a relativistic theory of Love numbers, which applies to compact bodies with strong internal gravities; the theory extends and completes a recent work by Flanagan and Hinderer, which revealed that the tidal Love number of a neutron star can be measured by Earth-based gravitational-wave detectors. We consider a spherical body deformed by an external tidal field, and provide precise and meaningful definitions for electric-type and magnetic-type Love numbers; and these are computed for polytropic equations of state. The theory applies to black holes as well, and we find that the relativistic Love numbers of a nonrotating black hole are all zero.

We discuss the prospects for bounding and perhaps even measuring quantum gravity effects on the dispersion of light using the highest-energy photons produced in gamma-ray bursts (GRBs) measured by the Fermi telescope. These prospects are brighter than might have been expected, as in the first ten months of operation, Fermi has so far reported eight events with photons over 100 MeV seen by its Large Area Telescope. We review features of these events which may bear on Planck-scale phenomenology, and we discuss the possible implications for alternative scenarios for in-vacua dispersion coming from breaking or deforming of Poincaré invariance. Among these are semiconservative bounds (which rely on some relatively weak assumptions about the sources) on subluminal and superluminal in-vacuo dispersion. We also propose that it may be possible to look for the arrival of still higher-energy photons and neutrinos from GRBs with energies in the range ${10}^{14}–{10}^{17}\mathrm{eV}$. In some cases the quantum gravity dispersion effect would predict these arrivals to be delayed or advanced by days to months from the GRB, giving a clean separation of astrophysical source and spacetime propagation effects.

In this work, we study the emission of tensor-type gravitational degrees of freedom from a higher-dimensional, simply rotating black hole in the bulk. The decoupled radial part of the corresponding field equation is first solved analytically in the limit of low-energy emitted particles and low-angular momentum of the black hole in order to derive the absorption probability. Both the angular and radial equations are then solved numerically, and the comparison of the analytical and numerical results shows a very good agreement in the low and intermediate energy regimes. By using our exact, numerical results we compute the energy and angular-momentum emission rates and their dependence on the spacetime parameters such as the number of additional spacelike dimensions and the angular momentum of the black hole. Particular care is given to the convergence of our results in terms of the number of modes taken into account in the calculation and the multiplicity of graviton tensor modes that correspond to the same angular-momentum numbers.

Dark and baryonic matter contribute comparable energy density to the present universe. The dark matter may also be responsible for the cosmic positron and electron excesses. We connect these phenomena with the Dirac seesaw for neutrino masses. In our model (i) the dark matter relic density is a dark matter asymmetry generated simultaneously with the baryon asymmetry so that we can naturally understand the coincidence between the dark and baryonic matter and (ii) the dark matter mostly decays into the leptons so that its decay can interpret the anomalous cosmic rays with positron and electron excesses.

Hadrons are composite objects made of quarks and gluons, and during a collision one can have several elementary interactions between the constituents. These elementary interactions, using an appropriate theoretical framework, can be related to the total and elastic cross sections. At high c.m. energy it also becomes possible to identify experimentally a high $p_{\perp }$ subset of the parton interactions and to study their multiplicity distribution. Predictions of the multiple interaction rates are difficult because in principle one needs to have a knowledge of the correlated parton distribution functions that describe the probability to find simultaneously different partons in different elements of phase space. In this work we address this question and suggest a method to describe effectively the fluctuations in the instantaneous configuration of a colliding hadron. This problem is intimately related to the origin of the inelastic diffractive processes. We present a new method to include the diffractive cross section in an eikonal formalism that is equivalent to a multichannel eikonal. We compare with data and present an extrapolation to higher energy.