We present an inflationary model that is geodesically complete and does not suffer from the trans-Planckian problem. In most inflationary models, massless (conformal) scalar field fluctuations in a de Sitter background gives rise to a scale-invariant spectrum. In this work, we realize scale-invariant perturbations from thermal fluctuations in (conformal) radiation during a radiation dominated contraction era prior to inflation. As the modes exit the Hubble radius during the contraction phase, scale-invariant fluctuations are generated. After many cycles, we enter into a power-law inflationary phase, that stretches the modes produced in the previous contraction phase to scales that we observe today.

We investigate the linear cosmological perturbations of Hořava-Lifshitz gravity in a Friedmann-Robertson-Walker universe without any matter. Our results show that a new gauge-invariant dynamical scalar mode emerges, due to the gauge transformation under the “foliation-preserving” diffeomorphism and “projectability condition,” and it can produce a scale invariant power spectrum. In the infrared regime with $\lambda =1$, the dynamical scalar degree of freedom turns to be a nondynamical one at the linear order level.

Cosmologically long-lived, composite states arise as natural dark matter candidates in theories with a strongly interacting hidden sector at a scale of 10–100 TeV. Light axionlike states, with masses in the 1 MeV–10 GeV range, are also generic, and can decay via Higgs couplings to light standard model particles. Such a scenario is well motivated in the context of very low-energy supersymmetry breaking, where ubiquitous cosmological problems associated with the gravitino are avoided. We investigate the astrophysical and collider signatures of this scenario, assuming that dark matter decays into the axionlike states via dimension six operators, and we present an illustrative model exhibiting these features. We conclude that the recent data from PAMELA, FERMI, and H.E.S.S. points to this setup as a compelling paradigm for dark matter. This has important implications for future diffuse gamma ray measurements and collider searches.

Once new particles are discovered at the LHC and their masses are measured, it will be of crucial importance to determine their spin, in order to identify the underlying new physics model. We investigate the method first suggested by Barr and later extended by others to distinguish between supersymmetry and alternative models, e.g. universal extra dimensions, in a certain cascade decay. This method uses invariant mass distributions of the outgoing standard model particles to measure the spin of intermediate particles, by exploiting the quark/antiquark asymmetry of the LHC as a $pp$ collider, which is limited for first generation quarks. In this work, we suggest instead to measure the charge of the outgoing quark, in case it is a third generation quark. The resulting asymmetry for a bottom quark is similar to the previous method, while it is independent of hadronic uncertainties. Furthermore, for a top quark, the asymmetry allows better distinction between the models, as demonstrated by a quantitative analysis of model discrimination. We also show that the top’s decay products can be used instead of the top itself, when the reconstruction of the top momentum is difficult to accomplish, and still provide information about the spin.

A new mechanism for heavy quarkonium production in high-energy collisions called the “$s$-channel cut” was proposed in 2005 by Lansberg, Cudell, and Kalinovsky. We identify this mechanism physically as the production of a heavy quark and antiquark that are on-shell followed by their rescattering to produce heavy quarkonium. We point out that in the nonrelativistic QCD factorization formalism this rescattering mechanism is a contribution to the color-singlet model term at next-to-next-to-leading order in perturbation theory. Its leading contribution to the production rate can be calculated without introducing any additional phenomenological parameters. We calculate the charm-pair rescattering (or $s$-channel cut) contribution to the production of $J/\psi$ at the Tevatron and compare it to estimates by Lansberg et al. using phenomenological models. This contribution competes with the leading-order term in the color-singlet model at large transverse momentum but is significantly smaller than the next-to-leading-order term. We conclude that charm-pair rescattering is not a dominant mechanism for charmonium production in high-energy collisions.

We performed ultracold neutron storage measurements to search for additional losses due to neutron ($n$) to mirror-neutron ($n^{\prime }$) oscillations as a function of an applied magnetic field $B$. In the presence of a mirror magnetic field $B^{\prime }$, ultracold neutron losses would be maximal for $B\approx B^{\prime }$. We did not observe any indication for $n{n}^{\prime }$ oscillations and placed a lower limit on the oscillation time of ${\tau }_{n{n}^{\prime }}>12.0\mathrm{s}$ at 95% C.L. for any $B^{\prime }$ between 0 and $12.5\mu \mathrm{T}$.

We construct dynamical black ring solutions in the five-dimensional Einstein-Maxwell system with a positive cosmological constant and investigate the geometrical structure. The solutions describe the physical process such that a thin black ring at early time shrinks and changes into a single black hole as time increases. We also discuss the multiblack rings and the coalescence of them.

We provide a detailed analysis of quantum field theory around a collapsing shell and discuss several conceptual issues related to the emission of radiation flux and formation of black holes. Explicit calculations are performed using a model for a collapsing shell, which turns out to be analytically solvable. We use the insights gained in this model to draw reliable conclusions regarding more realistic models. We first show that any shell of mass $M$, which collapses to a radius close to $r=2M$, will emit approximately thermal radiation for a period of time. In particular, a shell that collapses from some initial radius to a final radius $2M(1-{ϵ}^2{)}^{-1}$ (where $ϵ\ll 1$) without forming a black hole, will emit thermal radiation during the period $M\lesssim t\lesssim M\ln (1/{ϵ}^2)$. Later on ($t\gg M\ln (1/{ϵ}^2)$), the flux from such a shell will decay to zero exponentially. We next study the effect of backreaction computed using the vacuum expectation value of the stress tensor on the collapse. We find that, in any realistic collapse scenario, the backreaction effects do not prevent the formation of the event horizon. The time at which the event horizon is formed is, of course, delayed due to the radiated flux—which decreases the mass of the shell—but this effect is not sufficient to prevent horizon formation. We also clarify several conceptual issues and provide pedagogical details of the calculations in the Appendices to the paper.

We present a set of formalisms for comparing, evolving, and constraining primordial non-Gaussian models through the CMB bispectrum. We describe improved methods for efficient computation of the full CMB bispectrum for any general (nonseparable) primordial bispectrum, incorporating a flat sky approximation and a new cubic interpolation. We review all the primordial non-Gaussian models in the present literature and calculate the CMB bispectrum up to $l<2000$ for each different model. This allows us to determine the observational independence of these models by calculating the cross correlation of their CMB bispectra. We are able to identify several distinct classes of primordial shapes—including equilateral, local, warm, flat, and feature (non-scale invariant)—which should be distinguishable given a significant detection of CMB non-Gaussianity. We demonstrate that a simple shape correlator provides a fast and reliable method for determining whether or not CMB shapes are well correlated. We use an eigenmode decomposition of the primordial shape to characterize and understand model independence. Finally, we advocate a standardized normalization method for $f_{\mathrm{NL}}$ based on the shape autocorrelator, so that observational limits and errors $\Delta f_{\mathrm{NL}}$ can be consistently compared for different models.

Despite compelling arguments that significant discoveries of physics beyond the standard model are likely to be made at the Large Hadron Collider, it remains possible that this machine will make no such discoveries, or will make no discoveries directly relevant to the dark matter problem. In this article, we study the ability of astrophysical experiments to deduce the nature of dark matter in such a scenario. In most dark matter studies, the relic abundance and detection prospects are evaluated within the context of some specific particle physics model or models (e.g., supersymmetry). Here, assuming a single weakly interacting massive particle constitutes the Universe’s dark matter, we attempt to develop a model-independent approach toward the phenomenology of such particles in the absence of any discoveries at the Large Hadron Collider. In particular, we consider generic fermionic or scalar dark matter particles with a variety of interaction forms, and calculate the corresponding constraints from and sensitivity of direct and indirect detection experiments. The results may provide some guidance in disentangling information from future direct and indirect detection experiments.

Phase space and attractor dimensions in a gravitational wave detector output can be estimated in order to identify chaotic (deterministic) signals in the presence of additive Gaussian noise. These quantities are evaluated, respectively, by means of conditional probabilities and the Grassberger-Procaccia algorithm, both methods relying on embedding in a suitable space of dimension $d$. By testing with different embedding dimensions, a deterministic—though erratic—signal can be detected by comparing the corresponding conditional probabilities via Kolmogorov-Smirnoff test and checking whether the correlation (fractal) dimension differs from $d$. Results of the two approaches are eventually compared, both for chaotic and periodic trajectories.

Chern-Simons modified gravity is a string theory and loop-quantum-gravity inspired effective theory that modifies general relativity by adding a parity-violating Pontryagin density to the Einstein-Hilbert action multiplied by a coupling scalar. We strongly constrain nondynamical Chern-Simons modified gravity with a timelike Chern-Simons scalar through observations of the double-binary-pulsar PSR J0737-3039A/B. We first calculate Chern-Simons corrections to the orbital evolution of binary systems. We find that the ratio of the correction to periastron precession to the general relativistic prediction scales quadratically with the semimajor axis and inversely with the square of the object’s radius. Binary pulsar systems are thus ideal to test this theory, since periastron precession can be measured with subdegree accuracies and the semimajor axis is millions of times larger than the stellar radius. Using data from PSR J0737-3039A/B we dramatically constrain the nondynamical Chern-Simons coupling to $M_{\mathrm{CS}}≔1/|\dot{\vartheta }|>33\mathrm{meV}$, approximately a hundred billion times better than current Solar System tests.

We present the details of a deconstructed model that incorporates both Higgsless and top-color mechanisms. The model alleviates the tension between obtaining the correct top quark mass and keeping $\Delta \rho$ small that exists in many Higgsless models. It does so by singling out the top quark mass generation as arising from a Yukawa coupling to an effective top Higgs which develops a small vacuum expectation value, while electroweak symmetry breaking results largely from a Higgsless mechanism. As a result, the heavy partners of the SM fermions can be light enough to be seen at the LHC. After presenting the model, we detail the phenomenology, showing that for a broad range of masses, these heavy fermions are discoverable at the LHC.

Monte Carlo renormalization group (MCRG) methods were designed to study the nonperturbative phase structure and critical behavior of statistical systems and quantum field theories. I adopt the 2-lattice matching method used extensively in the 1980’s and show how it can be used to predict the existence of nonperturbative fixed points and their related critical exponents in many flavor SU(3) gauge theories. This work serves to test the method and I study relatively well understood systems: the $N_f=0$, 4 and 16 flavor models. The pure gauge and $N_f=4$ systems are confining and chirally broken and the MCRG method can predict their bare step scaling functions. Results for the $N_f=16$ model indicate the existence of an infrared fixed point with nearly marginal gauge coupling. I present preliminary results for the scaling dimension of the mass at this new fixed point.

We analyze the inclusive $b(c)\to s(u){\mu }^{+}{\mu }^{-}$ and exclusive $B(D^{+})\to K({\pi }^{+}){\mu }^{+}{\mu }^{-}$ flavor changing neutral current decays in light of the HyperCP boson $X^0$ of mass 214 MeV recently observed in the hyperon decay ${\Sigma }^{+}\to p{\mu }^{+}{\mu }^{-}$. Using the branching ratio data of the respective inclusive and exclusive decays, we obtain constraints on $g_1(h_1)$ and $g_2(h_2)$, the scalar and pseudoscalar coupling constants of the $b-s-X^0(c-u-X^0)$ vertices.

We compute the static energy of QCD at short distances at next-to-next-to-next-to-leading logarithmic accuracy in terms of the three-loop singlet potential. By comparing our results with lattice data we extract the value of the unknown piece of the three-loop singlet potential.

We present total and differential cross sections for $Wb\overline{b}$ and $Zb\overline{b}$ production at the CERN Large Hadron Collider with a center-of-mass energy of $\sqrt{s}=14\mathrm{TeV}$, including next-to-leading order (NLO) QCD corrections and full bottom-quark mass effects. We also provide numerical results obtained with a center-of-mass energy of $\sqrt{s}=10\mathrm{TeV}$. We study the scale uncertainty of the total cross sections due to the residual renormalization- and factorization-scale dependence of the truncated perturbative series. While in the case of $Zb\overline{b}$ production the scale uncertainty of the total cross section is reduced by NLO QCD corrections, the $Wb\overline{b}$ production process at NLO in QCD still suffers from large scale uncertainties, in particular, in the inclusive case. We also perform a detailed comparison with a calculation that considers massless bottom quarks, as implemented in the Monte Carlo program MCFM. The effects of a nonzero bottom-quark mass ($m_b$) cannot be neglected in phase-space regions where the relevant kinematic observable, such as the transverse-momentum of the bottom quarks or the invariant-mass of the bottom-quark pair, are of the order of $m_b$. The effects on the total production cross sections are usually smaller than the residual scale uncertainty at NLO in QCD.

We reinterpret the proof of the Riemannian Penrose inequality by Bray. The modified argument turns out to have a nice feature so that the flow of Riemannian metrics appearing in Bray’s proof gives a Lorentzian metric of a spacetime. We also discuss a possible extension of our approach to charged black holes.

In the present work, we study the quantum cosmology description of Friedmann-Robertson-Walker models in the presence of a generic perfect fluid and a cosmological constant, which may be positive or negative. We work in Schutz’s variational formalism and the three-dimensional spatial sections may have positive, negative, or zero constant curvature. If one uses the scale factor and its canonically conjugated momentum as the phase space variables that describe the geometrical sector of these models, one obtains Wheeler-DeWitt equations with operator ordering ambiguities. In order to avoid those ambiguities and simplify the quantum treatment of the models, we follow references [Edésio M. Barbosa, Jr. and Nivaldo A. Lemos, Gen. Relativ. Gravit. 38, 1609 (2006).][Edésio M. Barbosa, Jr. and Nivaldo A. Lemos, Phys. Rev. D 78, 023504 (2008).] and introduce new phase space variables. We explicitly demonstrate, using the symplectic method, that the transformation leading from the old set of variables to the new one is canonical.

In this paper we present the structure of the renormalization group in non-Abelian Nambu-Jona-Lasinio model up to 1-loop order. The model is not perturbatively renormalizable in the usual power counting sense, but it is treated as an effective theory, valid in a scale of energy in which $p\ll \Lambda$, where $p$ is the external momenta of the loop and $\Lambda$ is a massive parameter that characterizes the couplings of the nonrenormalizable vertex. We clarify the tensorial structure of the interaction vertices and calculate the functions of the renormalization group. The analysis of the fixed points of the theory is also presented using Zimmermann’s procedure for reducing the coupling constants. We find that the origin is an infrared-stable fixed point at low energies and also there is a nontrivial ultraviolet stable fixed point, indicating that the theory could be perturbatively investigated in the low momentum regime.