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Articles **1** - **29** of ** 29**

## Full-Text Articles in Physics

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

#### Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

*Marco Cavaglia*

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk ...

Two-Dimensional Black Holes As Open Strings: A New Realization Of The Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

#### Two-Dimensional Black Holes As Open Strings: A New Realization Of The Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

*Marco Cavaglia*

We show that weak-coupled two-dimensional dilation gravity on anti-de Sitter space can be described by the dynamics of an open string. Neumann and Dirichlet boundary conditions for the string lead two different realizations of the anti-de Sitter/Conformal Field Theory correspondence. In particular, in the Dirichlet case the thermodynamical entropy of two-dimensional black holes can be exactly reproduced by counting the string states.

Tev Black Hole Fragmentation And Detectability In Extensive Air Showers, Eun-Joo Ahn, Maximo Ave, Marco Cavaglia, Angela V. Olinto

#### Tev Black Hole Fragmentation And Detectability In Extensive Air Showers, Eun-Joo Ahn, Maximo Ave, Marco Cavaglia, Angela V. Olinto

*Marco Cavaglia*

In models with large extra dimensions, particle collisions with a center-of-mass energy larger than the fundamental gravitational scale can generate nonperturbative gravitational objects. Since cosmic rays have been observed with energies above 10^{8} TeV, gravitational effects in the TeV energy range can, in principle, be observed by ultrahigh energy cosmic ray detectors. We consider the interaction of ultrahigh energy neutrinos in the atmosphere and compare extensive air showers from TeV black hole formation and fragmentation with standard model processes. Departures from the standard model predictions arise in the interaction cross sections and in the multiplicity of secondary particles. Large ...

Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini

#### Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini

*Marco Cavaglia*

We discuss the cosmological amplification of tensor perturbations in a simple example of brane-world scenario, in which massless gravitons are localized on a higher-dimensional Kasner-like brane embedded in a bulk AdS background. Particular attention is paid to the canonical normalization of the quadratic action describing the massless and massive vacuum quantum fluctuations, and to the exact mass-dependence of the amplitude of massive fluctuations on the brane. The perturbation equations can be separated. In contrast to de Sitter models of brane inflation, we find no mass gap in the spectrum and no enhancement for massless modes at high curvature. The massive ...

Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

#### Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

*Marco Cavaglia*

We present a detailed discussion of the duality between dilaton gravity on AdS_{2} and open strings. The correspondence between the two theories is established using their symmetries and field theoretical, thermodynamic, and statistical arguments. We use the dual conformai field theory to describe two-dimensional black holes. In particular, all the semiclassical features of the black holes, including the entropy, have a natural interpretation in terms of the dual microscopic conformai dynamics. The previous results are discussed in the general framework of the anti-de Sitter/conformal field theory dualities.

Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

#### Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

*Marco Cavaglia*

We propose that higher-dimensional extended objects (*p*-branes) are created by super-Planckian scattering processes in theories with TeV scale gravity. As an example, we compute the cross section for *p*-brane creation in a (*n* + 4)-dimensional spacetime with asymmetric compactification. We find that the cross section for the formation of a brane which is wounded on a compact submanifold of size of the fundamental gravitational scale is larger than the cross section for the creation of a spherically symmetric black hole. Therefore, we predict that branes are more likely to be created than black holes in super-Planckian scattering processes ...

Black Hole Multiplicity At Particle Colliders (Do Black Holes Radiate Mainly On The Brane?), Marco Cavaglia

#### Black Hole Multiplicity At Particle Colliders (Do Black Holes Radiate Mainly On The Brane?), Marco Cavaglia

*Marco Cavaglia*

If gravity becomes strong at the TeV scale, we may have the chance to produce black holes at particle colliders. In this Letter we revisit some phenomenological signatures of black hole production in TeV-gravity theories. We show that the bulk-to-brane ratio of black hole energy loss during the Hawking evaporation phase depends crucially on the black hole greybody factors and on the particle degrees of freedom. Since the greybody factors have not yet been calculated in the literature, and the particle content at trans-Planckian energies is not known, it is premature to claim that the black hole emits mainly on ...

Approximately Self-Similar Critical Collapse In 2+1 Dimensions, Marco Cavaglia, Gerard Clement, Alessandro Fabbri

#### Approximately Self-Similar Critical Collapse In 2+1 Dimensions, Marco Cavaglia, Gerard Clement, Alessandro Fabbri

*Marco Cavaglia*

Critical collapse of a self-gravitating scalar field in a (2+1)-dimensional spacetime with negative cosmological constant seems to be dominated by a continuously self-similar solution of the field equations without cosmological constant. However, previous studies of linear perturbations in this background were inconclusive. We extend the continuously self-similar solutions to solutions of the field equations with negative cosmological constant, and analyze their linear perturbations. The extended solutions are characterized by a continuous parameter. A suitable choice of this parameter seems to improve the agreement with the numerical results. We also study the dynamics of the apparent horizon in the ...

Synthesis, Characterization And Nonlinear Optical Properties Of Silver/Pva Nanocomposites, Mahdi Shahmiri

#### Synthesis, Characterization And Nonlinear Optical Properties Of Silver/Pva Nanocomposites, Mahdi Shahmiri

*mahdi shahmiri*

Silver/polyvinyl alcohol (PVA) nanocomposites are prepared via quick precipitation method, using hydrazine as a reducing agent. Preparing of silver/PVA nanocomposites by this method is done for the first time. The samples are characterized by Uv-Visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM). Nonlinear optical properties are carried out by Z-scan technique using a blue CW laser beam operated at wavelength 405 nm. It is shown that the synthesized samples have negative nonlinear refractive index and the magnitude is in the order of 108. The nonlinear refractive index increases as amount of reducing agent increases.

Fabrication And Characterization Of Graphene Hydrogel Via Hydrothermal Approach As A Scaffold For Preliminary Study Of Cell Growth, Huang Nay Ming

#### Fabrication And Characterization Of Graphene Hydrogel Via Hydrothermal Approach As A Scaffold For Preliminary Study Of Cell Growth, Huang Nay Ming

*Huang Nay Ming*

Three-dimensional assembly of graphene hydrogel is rapidly attracting the interest of researchers because of its wide range of applications in energy storage, electronics, electrochemistry, and waste water treatment. Information on the use of graphene hydrogel for biological purposes is lacking, so we conducted a preliminary study to determine the suitability of graphene hydrogel as a substrate for cell growth, which could potentially be used as building blocks for biomolecules and tissue engineering applications. A three-dimensional structure of graphene hydrogel was prepared via a simple hydrothermal method using two-dimensional large-area graphene oxide nanosheets as a precursor. The concentration and lateral size ...

Electron And Hole Dynamics Of Inas∕Gaasinas∕Gaas Quantum Dot Semiconductor Optical Amplifiers, I. O'Driscoll, T. Piwonski, C. F. Schleussner, J. Houlihan, G. Huyet, R. J. Manning

#### Electron And Hole Dynamics Of Inas∕Gaasinas∕Gaas Quantum Dot Semiconductor Optical Amplifiers, I. O'Driscoll, T. Piwonski, C. F. Schleussner, J. Houlihan, G. Huyet, R. J. Manning

*Physical Sciences Articles*

Single-color and two-color pump-probe measurements are used to analyze carrier dynamics in InAs∕GaAs quantum dot amplifiers. The study reveals that hole recovery and intradot electron relaxation occur on a picosecond time scale, while the electron capture time is on the order of 10ps. A longer time scale of hundreds of picoseconds is associated with carrier recovery in the wetting layer, similar to that observed in quantum well semiconductor amplifiers.

Carrier Capture Dynamics Of Inas/Gaas Quantum Dots, T. Piwonski, I. O'Driscoll, J. Houlihan, G. Huyet, R. J. Manning, A. V. Uskov

#### Carrier Capture Dynamics Of Inas/Gaas Quantum Dots, T. Piwonski, I. O'Driscoll, J. Houlihan, G. Huyet, R. J. Manning, A. V. Uskov

*Physical Sciences Articles*

Carrier dynamics of a 1.3μm InAs∕GaAs quantum dot amplifier is studied using heterodyne pump-probe spectroscopy. Measurements of the recovery times versus injection current reveal a power law behavior predicted by a quantum dot rate equation model. These results indicate that Auger processes dominate the carrier dynamics.

Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini

#### Relic Gravitons On Kasner-Like Branes, Marco Cavaglia, G. De Risi, M. Gasperini

*Physics Faculty Research & Creative Works*

We discuss the cosmological amplification of tensor perturbations in a simple example of brane-world scenario, in which massless gravitons are localized on a higher-dimensional Kasner-like brane embedded in a bulk AdS background. Particular attention is paid to the canonical normalization of the quadratic action describing the massless and massive vacuum quantum fluctuations, and to the exact mass-dependence of the amplitude of massive fluctuations on the brane. The perturbation equations can be separated. In contrast to de Sitter models of brane inflation, we find no mass gap in the spectrum and no enhancement for massless modes at high curvature. The massive ...

Approximately Self-Similar Critical Collapse In 2+1 Dimensions, Marco Cavaglia, Gerard Clement, Alessandro Fabbri

*Physics Faculty Research & Creative Works*

Critical collapse of a self-gravitating scalar field in a (2+1)-dimensional spacetime with negative cosmological constant seems to be dominated by a continuously self-similar solution of the field equations without cosmological constant. However, previous studies of linear perturbations in this background were inconclusive. We extend the continuously self-similar solutions to solutions of the field equations with negative cosmological constant, and analyze their linear perturbations. The extended solutions are characterized by a continuous parameter. A suitable choice of this parameter seems to improve the agreement with the numerical results. We also study the dynamics of the apparent horizon in the ...

Heavy Quark Production By A Quasi-Classical Color Field In Proton-Nucleus Collisions, Kirill Tuchin

#### Heavy Quark Production By A Quasi-Classical Color Field In Proton-Nucleus Collisions, Kirill Tuchin

*Kirill Tuchin*

We calculate the inclusive heavy quark production cross section for proton-nucleus collisions at high energies. We perform calculation in a quasi-classical approximation (McLerran-Venugopalan model) neglecting all low-x evolution effects. The derived expression for the differential cross section can be applied for studying the heavy quark production in the central rapidity region at RHIC.

Qcd In Curved Space-Time: A Conformal Bag Model, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

#### Qcd In Curved Space-Time: A Conformal Bag Model, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

*Kirill Tuchin*

We construct an effective low energy Lagrangian using constraints imposed by the renormalization group. Degrees of freedom are gluons and a scalar glueball. This effective theory has a dual description as classical gluodynamics on a curved conformal background. Color fields are dynamically confined, and the strong coupling freezes at distances larger than the glueball size. We make specific predictions (in particular, on the Nc dependence of glueball properties) which can be tested in lattice simulations of gluodynamics.

Nuclear Modification Factor In D + Au Collisions: Onset Of Suppression In The Color Glass Condensate, Dmitri Kharzeev, Yuri V. Kovchegov, Kirill Tuchin

#### Nuclear Modification Factor In D + Au Collisions: Onset Of Suppression In The Color Glass Condensate, Dmitri Kharzeev, Yuri V. Kovchegov, Kirill Tuchin

*Kirill Tuchin*

We perform a quantitative analysis of the nuclear modification factor in deuteron-gold collisions R dAu within the Color Glass Condensate approach, and compare our results with the recent data from RHIC experiments. Our model leads to Cronin enhancement at mid-rapidity, while at forward rapidities it predicts strong suppression of R dAu at all PT due to low-x evolution. We demonstrate that our results are consistent with the data for dAu charged hadron spectra, R dAu and R CP recently reported for rapidities in the interval Î·=0-3.2 by the BRAHMS experiment at RHIC. We also make a prediction for ...

Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan

#### Order-Parameter Symmetry And Mode-Coupling Effects At Dirty Superconducting Quantum Phase Transitions, Rastko Sknepnek, Thomas Vojta, Rajesh Narayanan

*Physics Faculty Research & Creative Works*

We derive an order-parameter field theory for a quantum phase transition between a disordered metal and an exotic (non- s -wave) superconductor. Mode coupling effects between the order parameter and other fermionic soft modes lead to an effective long-range interaction between the anomalous density fluctuations which is reflected in singularities in the free energy functional. However, this long-range interaction is not strong enough to suppress disorder fluctuations. The asymptotic critical region is characterized by run-away flow to large disorder. For weak coupling, this asymptotic region is very narrow. It is preempted by a wide crossover regime with mean-field critical behavior ...

Black Hole Multiplicity At Particle Colliders (Do Black Holes Radiate Mainly On The Brane?), Marco Cavaglia

*Physics Faculty Research & Creative Works*

If gravity becomes strong at the TeV scale, we may have the chance to produce black holes at particle colliders. In this Letter we revisit some phenomenological signatures of black hole production in TeV-gravity theories. We show that the bulk-to-brane ratio of black hole energy loss during the Hawking evaporation phase depends crucially on the black hole greybody factors and on the particle degrees of freedom. Since the greybody factors have not yet been calculated in the literature, and the particle content at trans-Planckian energies is not known, it is premature to claim that the black hole emits mainly on ...

Tev Black Hole Fragmentation And Detectability In Extensive Air Showers, Eun-Joo Ahn, Maximo Ave, Marco Cavaglia, Angela V. Olinto

*Physics Faculty Research & Creative Works*

In models with large extra dimensions, particle collisions with a center-of-mass energy larger than the fundamental gravitational scale can generate nonperturbative gravitational objects. Since cosmic rays have been observed with energies above 10^{8} TeV, gravitational effects in the TeV energy range can, in principle, be observed by ultrahigh energy cosmic ray detectors. We consider the interaction of ultrahigh energy neutrinos in the atmosphere and compare extensive air showers from TeV black hole formation and fragmentation with standard model processes. Departures from the standard model predictions arise in the interaction cross sections and in the multiplicity of secondary particles. Large ...

Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

#### Brane Factories, Eun-Joo Ahn, Marco Cavaglia, Angela V. Olinto

*Physics Faculty Research & Creative Works*

We propose that higher-dimensional extended objects (*p*-branes) are created by super-Planckian scattering processes in theories with TeV scale gravity. As an example, we compute the cross section for *p*-brane creation in a (*n* + 4)-dimensional spacetime with asymmetric compactification. We find that the cross section for the formation of a brane which is wounded on a compact submanifold of size of the fundamental gravitational scale is larger than the cross section for the creation of a spherically symmetric black hole. Therefore, we predict that branes are more likely to be created than black holes in super-Planckian scattering processes ...

Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

#### Two-Dimensional Ds/Cft Correspondence, Mariano Cadoni, P. Carta, Marco Cavaglia, S. Mignemi

*Physics Faculty Research & Creative Works*

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk ...

Classical Gluodynamics In Curved Space-Time And The Soft Pomeron, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

#### Classical Gluodynamics In Curved Space-Time And The Soft Pomeron, Dmitri Kharzeev, Eugene Levin, Kirill Tuchin

*Kirill Tuchin*

QCD at the classical level possesses scale invariance which is broken by quantum effects. This "dimensional transmutation" phenomenon can be mathematically described by formulating classical gluodynamics in a curved, conformally flat, space-time with non-vanishing cosmological constant. We study QCD high-energy scattering in this theory. We find that the properties of the scattering amplitude at small momentum transfer are determined by the energy density of vacuum fluctuations. The approach gives rise to the power growth of the total hadron-hadron cross section with energy, i.e., the pomeron. The intercept of the pomeron and the multiplicity of produced particles are evaluated. We ...

Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

#### Open Strings, 2d Gravity, And Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

*Physics Faculty Research & Creative Works*

We present a detailed discussion of the duality between dilaton gravity on AdS_{2} and open strings. The correspondence between the two theories is established using their symmetries and field theoretical, thermodynamic, and statistical arguments. We use the dual conformai field theory to describe two-dimensional black holes. In particular, all the semiclassical features of the black holes, including the entropy, have a natural interpretation in terms of the dual microscopic conformai dynamics. The previous results are discussed in the general framework of the anti-de Sitter/conformal field theory dualities.

Two-Dimensional Black Holes As Open Strings: A New Realization Of The Ads/Cft Correspondence, Mariano Cadoni, Marco Cavaglia

*Physics Faculty Research & Creative Works*

We show that weak-coupled two-dimensional dilation gravity on anti-de Sitter space can be described by the dynamics of an open string. Neumann and Dirichlet boundary conditions for the string lead two different realizations of the anti-de Sitter/Conformal Field Theory correspondence. In particular, in the Dirichlet case the thermodynamical entropy of two-dimensional black holes can be exactly reproduced by counting the string states.

Higher Twist Corrections And Maxima For Dis On A Proton In The High Density Qcd Region, E. Gotsman, Eugene Levin, U. Maor, L. Mclerran, Kirill Tuchin

#### Higher Twist Corrections And Maxima For Dis On A Proton In The High Density Qcd Region, E. Gotsman, Eugene Levin, U. Maor, L. Mclerran, Kirill Tuchin

*Kirill Tuchin*

We show that the ratio of different structure functions have a maximum which depends on energy. We argue, using the Golec-Biernat and Wusthoff model as well as the eikonal approach, that these maxima are functions of the saturation scale. We analyze leading and higher twist contributions for different observables to check whether a kinematic region exists where high parton density effects can be detected experimentally.

The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin

#### The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin

*Kirill Tuchin*

We calculate the total cross section for two scalar particles scattering at high energies in Î»Ï†3 theory in five dimensions, four of which are usual Minkowski ones and the fifth is compact. It is shown that the cross section is dominated by exchange of Pomeron whose intercept is larger than in usual four-dimensional case.

Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker

#### Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker

*Physics Faculty Research & Creative Works*

The two-dimensional patterns in our small angle neutron scattering (SANS) experiments from rapidly moving aerosols are anisotropic. To test the kinematic theory of two-body scattering that describes the anisotropy, we conducted SANS experiments using a constant source of D_{2}O aerosol with droplets moving at ~440 m/s, and varied the neutron velocity from 267 to 800 m/s. The theoretically predicted anisotropy of the laboratory scattering intensities agrees well with the experimental results. Based on an analysis of the scattering intensity in the Guinier region, we also determined the particle velocity. The results are in very good agreement ...

A Simple Monochromatic Spark Discharge Light-Source, Chin Oi Hoong

#### A Simple Monochromatic Spark Discharge Light-Source, Chin Oi Hoong

*Chin Oi Hoong*

Spark light illumination has been used in high-speed photog-raphy since the beginning ofthe century and various designs ofthe spark discharge light source have since been reportedr with spark duration ranging from nanoseconds to millisec-onds. We report here a simple and easy to build spark dis-charge tube for operation as a monochromatic point light source. The design and construction ofthe spark discharge tube is shown in Fig. 1. The sharp-tip solid cone anode is made of stainless steel which is screwed onto a brass rod connected A compact spark discharge tube operated as a monochromatic light source at 587.5 nm ...