118586772
Features of heavy physics in the CMB power spectrum
The computation of the primordial power spectrum in multi-field inflation models requires us to correctly account for all relevant interactions between adiabatic and non-adiabatic modes around and after horizon crossing. One specific complication arises from derivative interactions induced by the curvilinear trajectory of the inflaton in a multi-dimensional field space. In this work we compute the power spectrum in general multi-field models and show that certain inflaton trajectories may lead to observationally significant imprints of `heavy' physics in the primordial power spectrum if the inflaton trajectory turns, that is, traverses a bend, sufficiently fast (without interrupting slow roll), even in cases where the modes normal to the trajectory have masses approaching the cutoff of our theory. We emphasize that turning is defined with respect to the geodesics of the sigma model metric, irrespective of whether this is canonical or non-trivial. The imprints generically take the form of damped superimposed oscillations on the power spectrum. In the particular case of two-field models, if one of the fields is sufficiently massive compared to the scale of inflation, we are able to compute an effective low energy theory for the adiabatic mode encapsulating certain relevant operators of the full multi-field dynamics. As expected, a particular characteristic of this effective theory is a modified speed of sound for the adiabatic mode which is a functional of the background inflaton trajectory and the turns traversed during inflation. Hence in addition, we expect non-Gaussian signatures directly related to the features imprinted in the power spectrum.
119513179
The cosmology of massless string modes
We consider the spacetime dynamics of a gas of closed strings in the context of general relativity in a background of arbitrary spatial dimensions. Our motivation is primarily late time string gas cosmology, where such a spacetime picture has to emerge after the dilaton has stabilized. We find that after accounting for the thermodynamics of a gas of strings, only string modes which are massless at the self-dual radius are relevant, and that they lead to a dynamics which is qualitatively different from that induced by the modes usually considered in the literature. In the context of an ansatz with three large spatial dimensions and an arbitrary number of small extra dimensions, we obtain isotropic stabilization of these extra dimensions at the self-dual radius. This stabilization occurs for fixed dilaton, and is induced by the special string states we focus on. The three large dimensions undergo a regular Friedmann–Robertson–Walker expansion. We also show that this framework for late time cosmology is consistent with observational bounds.
119275413
On Semi-classical Degravitation and the Cosmological Constant Problems
In this report, we discuss a candidate mechanism through which one might address the various cosmological constant problems. We first observe that the renormalization of gravitational couplings (induced by integrating out various matter fields) manifests non-local modifications to Einstein’s equations as quantum corrected equations of motion. That is, at the loop level, matter sources curvature through a gravitational coupling that is a non-local function of the covariant d’Alembertian. If the functional form of the resulting Newton’s ‘constant’ is such that it annihilates very long wavelength sources, but reduces to 1=M 2 (Mpl being the 4d Planck mass) for all sources with cosmologically observable wavelengths, we would have a complimentary realization of the degravitation paradigm– a realization through which its non-linear completion and the corresponding modified Bianchi identities are readily understood. We proceed to consider various theories whose coupling to gravity may a priori induce non-trivial renormalizations of Newton’s constant in the IR, and arrive at a class of non-local effective actions which yield a suitably degravitating filter function for Newton’s constant upon subsequently being integrated out. We motivate this class of non-local theories through several considerations, discuss open issues, future directions, the inevitable question of scheme dependence in semi-classical gravitational calculations and comment on connections with other meditations in the literature on relaxing of the cosmological constant semi-classically.
119076672
D0 Matrix Mechanics: Topological Dynamics of Fuzzy Spaces
We consider the physics of a matrix model describing D0-brane dynamics in the presence of an RR flux background. Non-commuting spaces arise as generic soltions to this matrix model, among which fuzzy spheres have been studied extensively as static solutions at finite N. The existence of topologicaly distinct static configurations suggests the possibility of D-brane topology change within this model, however a dynamical solution interpolating between topologies is still somewhat elusive. In this paper, we study this model in the limit of infinite dimensional matrices, where new solutions-- the fuzzy cylinder and the fuzzy plane among them-- appear. We argue that any dynamics which involves topology change will likely only occur in this limit, after which we study the decay of a fuzzy cylinder into an infinite collection of fuzzy spheres as both a classical and a quantum phenomenon. We conclude from this excercise that in certain limits, matrix models offer a viable framework in which to study topological dynamics, and could perhaps be a precursor to a viable theory of space-time topological dynamics.
119088066
UV/IR mode mixing and the CMB
It is well understood that spatial noncommutativity, if indeed realized in nature, is a phenomenon whose effects are not just felt at energy scales comparable to the noncommutativity scale. Loop effects can transmit signatures of any underlying noncommutativity to macroscopic scales (a manifestation of a phenomenon that has come to be known as UV/IR mode mixing) and offer a potential lever to constrain the amount of noncommutativity present in nature, if present at all. Field theories defined on noncommutative spaces (realized in string theory when D-branes are coupled to backgrounds of nontrivial RR background flux), can exhibit strong UV/IR mode mixing, manifesting in a nonlocal one-loop effective action. In the context of inflation in the presence of any background noncommutativity, we demonstrate how this UV/IR mixing at the loop level can allow us to place severe constraints on the scale of noncommutativity if we presume inflation is responsible for large-scale structure. We demonstrate that any amount of noncommutativity greatly suppresses the cosmic microwave background power at all observable scales, independent of the scale of inflation, and independent of whether or not the noncommutativity tensor redshifts during inflation, therefore nullifying a very salient and successful prediction of inflation.
118490430
CMB imprints of a pre-inflationary climbing phase
We discuss the implications for cosmic microwave background (CMB) observables, of a class of pre-inflationary dynamics suggested by string models where SUSY is broken due to the presence of D-branes and orientifolds preserving incompatible portions of it. In these models the would-be inflaton is forced to emerge from the initial singularity climbing up a mild exponential potential, until it bounces against a steep exponential potential of ``brane SUSY breaking'' scenarios, and as a result the ensuing descent gives rise to an inflationary epoch that begins when the system is still well off its eventual attractor. If a pre-inflationary climbing phase of this type had occurred within 6-7 e-folds of the horizon exit for the largest observable wavelengths, displacement off the attractor and initial-state effects would conspire to suppress power in the primordial scalar spectrum, enhancing it in the tensor spectrum and typically superposing oscillations on both. We investigate these imprints on CMB observables over a range of parameters, examine their statistical significance, and provide a semi-analytic rationale for our results. It is tempting to ascribe at least part of the large-angle anomalies in the CMB to pre-inflationary dynamics of this type.
120805707
Weak interactions with scalar intermediate bosons
Abstract A theory of weak interactions with scalar bosons is considered. it is pointed out that if the bosons couple to a triplet of scalar and pseudoscalar currents with unequal strength, we get a consistent theory, with weak parity and strangeness violations, and with effective octet structure for the strangeness-changing non-leptonic interaction. Higher-order weak and electromagnetic processes are evaluated under the assumption that the lowest order weak and electromagnetic processes are renormalizable and finite. The calculations for K L 0 → μ + μ − , K + → π + μ + μ − and K 1 0 K 2 0 mass difference yield consistent results for a scalar boson mass of about 10 GeV.
119961571
THE NUCLEON AND THE ROPER RESONANCE.
122034057
Ground-state energy of two-dimensional weakly coupled Hamiltonians
It is observed' that a short-range attractive potential always produces a bound state in one or two dimensions. While this property has attracted considerable attention for one-dimensional potentials, leading to many general results, ' ' much less is known about the corresponding property in two dimensions. This may be due to the fact that the bound state is marginal in the case of two dimensions, and somewhat harder to analyze. Apart from the original result of Landau and Lifshitz, ' the only other results known for the two-dimensional problem are those obtained by Simon. ' For the two-dimensional Ham iltonian verse of the T matrix, thus allowing a perturbative description of the poles of the T matrix and hence the bound-state energies. In our present note, the ground-state energy of Hmniltonian (1) is analyzed using the Noyes form' of the T matrix. We find that for potentials satisfying conditions (2) and (3), the ground-state energy has an asymptotic series given by
121285502
Nonpolynomial anharmonic oscillator
119717796
A non-polynomial Lee-like model without ghosts
Abstract A Lee-like non-polynomial Lagrangian is discussed. The fourth order calculations in the major coupling, for the propagator function are finite but dominate over the second order terms, asymptotically. This implies that for using non-polynomial Lagrangians at high energy, one must include the higheer order terms in the major coupling. It is shown that the model has no ghosts, but does not satisfy the theorem of Lehmann, Symanzik and Zimmermann.