Effective equation of state and energy conditions in phantom/tachyon inflationary cosmology perturbed by quantum effects

We discuss the model consisting of tachyon which may have the negative kinetic energy plus scalar phantom and plus conformal quantum matter. It is demonstrated that such a model naturally admits two deSitter phases where the early universe inflation is produced by quantum effects and the late time accelerating universe is caused by phantom/tachyon. The energy conditions bounds for such cosmology are derived. It is interesting that effective equation of state may change its sign which depends from the proper choice of the combination of phantom/tachyon and quantum effects.Comment: LaTeX file 14 pages, references are adde

Dynamic pricing in regulated automobile insurance markets with heterogeneous insurers: Strategies nice versus nasty for customers ☆

This study examines a phenomenon in one nation's automobile insurance market where insurers adopt diverse pricing strategies in this regulated industry that does not allow for such diversions-a homogeneous, insurance industry in which a government authority sets the official pricing formula as well as all of the rating factors. Insurers use a claim coefficient that reflects previous claim records of policyholder as an implicit pricing tool to over/under charge new and repeat customers. The aim here is not so much to blow-the-whistle on pricing practices that violate regulations but to describe execution details of the practices and their outcomes. The results show that firm-level, systematic, price variances that occur differ from prices that follow from applying regulated individual-claim coefficients. Based on the unique firm-level pricing strategies, this study finds that some insurers are more nice to new customers and nasty to repeat customers to increase market shares while other insurers earn high profits by being nasty to repeat customers. The assumption that a behavioral primacy effect may exist in the market may guide some firms' pricing strategies

Steep Inflation followed by Born-Infeld Reheating

We discuss a model in which high energy brane corrections allow a single scalar field to describe inflation at early epochs and quintessence at late times. The reheating mechanism in the model originates from Born-Infeld matter whose energy density mimics cosmological constant at very early times and manifests itself as radiation subsequently. For most of the inflationary evolution the Born-Infeld matter remains subdominant to the the scalar field. Shortly before the end of inflation driven by the scalar field, the energy density of Born-Infeld matter starts scaling as radiation and drops by several orders of magnitudes at the epoch inflation ends. The problem of over production of gravity wave background in scenarios based upon reheating through gravitational particle production is successfully resolved by suitably fixing the initial value of radiation energy density at the end of inflation. No additional fine tuning of the parameters is required for a viable evolution.Comment: Final version accepted in PLB ; some clarifications and references adde

D-brane Dynamics in RR Deformation of NS5-branes Background and Tachyon Cosmology

We study D-brane dynamics in the gravity dual background of ODp theories using the effective action on the worldvolume of the brane. We explore the similarities of the system with the rolling tachyon, including the exponential decrease of pressure at late times. We also consider the case where the worldvolume theory on a D3-brane is coupled to gravity and construct a cosmological model. By considering the time reversal symmetric solutions, we find that we can have both closed and open universes depending on the initial value of the radial mode on the brane. We compare the models with tachyon driven cosmologies and find limits where slow roll inflation is realized.Comment: 24 pages, 5 figures, a subsection added on Maldacena-Nunez background. To be published in Nuclear Physics

Brane tachyon dynamics

The dynamics of a tachyon attached to a Dvali, Gabadadze and Porrati (DGP) brane is investigated. Exponential potential and inverse power law potential are explored, respectively. The quasi-attractor behavior, for which the universe will eventually go into a phase similar to the slow-roll inflation, is discovered in both cases of exponential potential and inverse power law potential. The equation of state (EOS) of the virtual dark energy for a single scalar can cross the phantom divide in the branch $\theta=-1$ for both potentials, while the EOS of the virtual dark energy for a single scalar can not cross this divide in the branch $\theta=1$.Comment: 20 pages, 12 figs, to appear in PL

The Mass, Normalization and Late Time behavior of the Tachyon Field

We study the dynamics of the tachyon field $T$. We derive the mass of the tachyon as the pole of the propagator which does not coincide with the standard mass given in the literature in terms of the second derivative of $V(T)$ or $Log[V(T)]$. We determine the transformation of the tachyon in order to have a canonical scalar field $\phi$. This transformation reduces to the one obtained for small $\dot T$ but it is also valid for large values of $\dot T$. This is specially interesting for the study of dark energy where $\dot T\simeq 1$. We also show that the normalized tachyon field $\phi$ is constrained to the interval $T_2\leq T \leq T_1$ where $T_1,T_2$ are zeros of the original potential $V(T)$. This results shows that the field $\phi$ does not know of the unboundedness of $V(T)$, as suggested for bosonic open string tachyons. Finally we study the late time behavior of tachyon field using the L'H\^{o}pital rule.Comment: 9 pages, 10 figure

Non-minimally Coupled Tachyonic Inflation in Warped String Background

We show that the non-minimal coupling of tachyon field to the scalar curvature, as proposed by Piao et al, with the chosen coupling parameter does not produce the effective potential where the tachyon field can roll down from T=0 to large $T$ along the slope of the potential. We find a correct choice of the parameters which ensures this requirement and support slow-roll inflation. However, we find that the cosmological parameter found from the analysis of the theory are not in the range obtained from observations. We then invoke warped compactification and varying dilaton field over the compact manifold, as proposed by Raeymaekers, to show that in such a setup the observed parameter space can be ensured.Comment: minor typos corrected and references adde

IMECE2009-10835 THE APPLICATION OF VACUUM CASTING SYSTEM FOR SIMPLIFYING THE DESIGN OF TRANSTIBIAL SOCKETS

ABSTRACT Prosthetic sockets are one of the most important pieces of equipment for a transtibial amputee to maintain a regular life. Rapid Prototyping is becoming mature and low-cost to fit the CAD system that can conserve the shapes of the stump and socket for reproducing the sockets. If the stump shape can be accurately obtained and the prosthetists' expertise can be included in a CAD system, then a prosthetic socket will be easily designed by a prosthetist. The stump was scanned to get the shape for the construction and modification of the stump model in a CAD system. However, the stump trembled during the scanning process, the scanner was sensitive about the skin move, so that the scanned data will not exactly represent the real stump shape. This study used a vacuum casting system to gain the stump model instead of creating a positive plaster model in the traditional process of fabricating prosthetic sockets. The stump shape under various vacuum pressures was obtained using a scanning machine and built in a CAD system. The CAD model of the stump will be modified to meet the load-bearing capability of the specific amputee. The use of the vacuum casting method is expected to simplify the design of a socket that will be fabricated by a rapid prototyping machine. Simplifying the designs of transtibial socket can decrease the dependence of human experience and promote the quality and stability of prosthetic sockets

Graphene on Au-coated SiOx substrate: Its core-level photoelectron micro-spectroscopy study

The core-level electronic structures of the exfoliated graphene sheets on a Au-coated SiOx substrate have been studied by synchrotron radiation photoelectron spectroscopy (SR-PES) on a micron-scale. The graphene was firstly demonstrated its visibility on the Au-coated SiOx substrate by micro-optical characterization, and then conducted into SR-PES study. Because of the elimination of charging effect, precise C 1s core-level characterization clearly shows graphitic and contaminated carbon states of graphene. Different levels of Au-coating-induced p-type doping on single- and double-layer graphene sheets were also examined in the C 1s core-level shift. The Au-coated SiOx substrate can be treated as a simple but high-throughput platform for in situ studying graphene under further hybridization by PES

Reconstructing the Equation of State of Tachyon

Recent progress in theoretical physics suggests that the dark energy in the universe might be resulted from the rolling tachyon field of string theory. Measurements to SNe Ia can be helpful to reconstruct the equation of state of the rolling tachyon which is a possible candidate of dark energy. We present a numerical analysis for the evolution of the equation of state of the rolling tachyon and derive the reconstruction equations for the equation of state as well as the potential.Comment: 6 pages, 3 figures, to appear Phys. Rev.