共查询到20条相似文献,搜索用时 234 毫秒
1.
A thermal gravitational wave background can be produced in the early Universe if a radiation dominated epoch precedes the usual inflationary stage. This background provides a unique way to study the initial state of the Universe. We discuss the imprint of this thermal spectra of gravitons on the cosmic microwave background (CMB) power spectra, and its possible detection by CMB observations. Assuming the inflationary stage is a pure de Sitter expansion we find that, if the number of e-folds of inflation is smaller than 65, the signal of this thermal spectrum can be detected by the observations of Planck and PolarBear experiments, or the planned EPIC experiments. This bound can be even looser if inflation-like stage is the sub-exponential. 相似文献
2.
Malcolm Fairbairn Tommi Markkanen David Rodriguez Roman 《The European Physical Journal C - Particles and Fields》2018,78(4):347
We consider the effect of the Gibbons–Hawking radiation on the inflaton in the situation where it is coupled to a large number of spectator fields. We argue that this will lead to two important effects – a thermal contribution to the potential and a gradual change in parameters in the Lagrangian which results from thermodynamic and energy conservation arguments. We present a scenario of hilltop inflation where the field starts trapped at the origin before slowly experiencing a phase transition during which the field extremely slowly moves towards its zero temperature expectation value. We show that it is possible to obtain enough e-folds of expansion as well as the correct spectrum of perturbations without hugely fine-tuned parameters in the potential (albeit with many spectator fields). We also comment on how initial conditions for inflation can arise naturally in this situation. 相似文献
3.
Artur Alho 《Physics letters. [Part B]》2011,703(5):537-542
We consider the evolution of covariant and gauge invariant linear density perturbations of scalar field cosmologies using a dynamical systems? approach. We find conditions for which the perturbations decay in time, so that the spacetime approaches a homogeneous solution which inflates, for quadratic and exponential potentials. This pre-inflationary homogenization is found to be stable in the potentials? parameter spaces. Furthermore, in each case, we determine the minimum size of the resultant homogeneous patch and show that, for quadratic potentials, the resulting inflationary solutions include those with the necessary number of e-folds. 相似文献
4.
Grating reflectors are a potential low-noise replacement for amorphous multilayer mirrors. We investigate the influence of polarization and refractive index on Brownian thermal noise of binary grating reflectors using Maxwell's stress tensor. Our results demonstrate that the refractive index of the grating material is a critical parameter for thermal noise in these structures. In contrast to multilayer mirrors, a low coating thickness does not necessarily lead to a low thermal noise amplitude for structures with low refractive index. We find that an improved noise performance of grating reflectors requires materials of refractive index ?2.5. We present a factorized expression for the thermal noise of grating reflectors made of arbitrary materials by simply scaling the noise amplitude with the related material parameters. 相似文献
5.
Jyotirmay Das Mandal Ujjal Debnath 《International Journal of Theoretical Physics》2017,56(6):1771-1783
We have discussed here Hessence inflation in Loop Quantum Cosmological background. In this work, we have emphasized on late times, taking into account various slow-roll conditions. This model has been constructed taking intermediate and logamediate scale factors. In both cases the forms of hessence field, potential, number of e-folds, slow-roll parameters are manipulated by taking the dissipative co-efficient Γ =Γ0, where Γ0 > 0 is a constant, in accordance with second law of thermodynamics. 相似文献
6.
Amna Ali Atri Deshamukhya Sudhakar Panda M. Sami 《The European Physical Journal C - Particles and Fields》2011,71(6):1672
We revisit our earlier investigations of the brane–antibrane inflation in a warped deformed conifold background, reported
in Phys. Lett. B 674, 131 (2009), where now we include the contributions to the inflation potential arising from imaginary anti-self-dual (IASD) fluxes including
the term with irrational scaling dimension discovered recently in and . We observe that these corrections to the effective potential help in relaxing the severe fine tunings associated with the
earlier analysis. Required number of e-folds, observational constraint on COBE normalization and low value of the tensor to
scalar ratio are achieved which is consistent with WMAP seven years data. 相似文献
7.
8.
We study a supergravity D-term chaotic inflationary model, in the context of the braneworld scenario, in particular we consider the Randal1-Sundrum model type 2. Using the latest release from the combination of WMAP9, eCMB, BAO, and Ho, we show that the inflation observables depend only on the number ore-folds N. We also derive all known spectrum inflationary parameters, which are widely consistent with WMAP9 data for a particular choice of values N specially for the scalar spectral index ns and the ratio r. However, the running of the scalar spectral index dns/dlnk is now excluded from the range given by the latest observational measurements. 相似文献
9.
We propose a universal method of computation of thermal noise in mirrors of gravitational wave interferometers based on first principles. We imagine a situation where a mirror is part of a Fabry–Perot cavity. The movement of the mirror's surface produces variation of the eigen frequency of the cavity, which is computed by evaluating the variation of the energy stored in cavity. We consider two particular examples: first, the thermal noise from a dielectric slab inside the Fabry–Perot cavity, and second, the polarization-dependent thermal noise in the folded cavity. 相似文献
10.
Hybrid linear amplifier-involved detection for continuous variable quantum key distribution with thermal states 下载免费PDF全文
《中国物理 B》2020,(5)
Continuous-variable quantum key distribution(CVQKD) can be integrated with thermal states for short-distance wireless quantum communications. However, its performance is usually restricted with the practical thermal noise. We propose a method to improve the security threshold of thermal-state(TS) CVQKD by employing a heralded hybrid linear amplifier(HLA) at the receiver. We find the effect of thermal noise on the HLA-involved scheme in near-and-mid infrared band or terahertz band for direct and reverse reconciliation. Numerical simulations show that the HLA-involved scheme can compensate for the detriment of thermal noise and hence increase the security threshold of TS-CVQKD. In near-and-mid infrared band, security threshold can be extended by 2.1 dB in channel loss for direct reconciliation and 1.6 dB for reverse reconciliation, whereas in terahertz band, security threshold can be slightly enhanced for the gain parameter less than 1 due to the rise in thermal noise. 相似文献
11.
Elizabeth Huynh Anel Medrano Arthur Zavala John R. Thompson 《Optics Communications》2008,281(4):836-845
We present a experimental and theoretical investigation of spontaneously initiated stimulated Brillouin scattering in which the interplay of two independent noise sources (thermal and pump) can be studied by controlling the relative importance of each source. We vary the pump noise by adding a controlled amount of Gaussian noise to the input pulses, and we control the contribution of the thermal noise by examining the energy statistics of both entire scattered pulses and of temporal slices of the scattered pulses. We show that the energy of the whole Stokes pulses follow a Gaussian distribution but that the energy of the Stokes pulse slices do not. 相似文献
12.
Various noise sources limit the sensitivity of current interferometric gravitational wave detectors, including seismic noise,
thermal noise of the optical components and suspension elements and photon shot noise. Plans are in place for a suite of hardware
upgrades which should increase the sensitivity of these detectors by reducing the various noise sources. With these designs
for 2nd generation detectors mature, techniques for further improvement of detector sensitivity by a factor of approximately
10 are under study. A particular challenge is the reduction of the thermal noise associated with the interferometer mirrors
and their suspensions. We review the current status of research on thermal noise in interferometric gravitational wave detectors.
Aspects of possible techniques for use in future ‘3rd generation detectors’ such as cryogenics and diffractive optics are
discussed. 相似文献
13.
We study the influence of thermal fluctuations on the dewetting dynamics of thin liquid films. Starting from the incompressible
Navier-Stokes equations with thermal noise, we derive a fourth-order degenerate parabolic stochastic partial differential
equation which includes a conservative, multiplicative noise term—the stochastic thin-film equation. Technically, we rely
on a long-wave-approximation and Fokker–Planck-type arguments. We formulate a discretization method and give first numerical
evidence for our conjecture that thermal fluctuations are capable of accelerating film rupture and that discrepancies with
respect to time-scales between physical experiments and deterministic numerical simulations can be resolved by taking noise
effects into account. 相似文献
14.
M. K. Sen A. Baura B. C. Bag 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(3):381-389
We have studied work fluctuation behaviour in the presence of internal thermal noise as
well as external coloured noise. The external coloured noise may have both Gaussian or
non-Gaussian characteristics. We have investigated the dependence of position and work
fluctuations on the properties of both the environments. For thermal noise driven systems,
there is a maximum in the variation of mean square fluctuation of work (MSFW) as a
function of damping strength at intermediate times, while at asymptotic long times MSFW
monotonically increases in the same damping regime. But for external noise, MSFW
monotonically decreases as a function of damping strength at intermediate times, whereas
at long times it becomes almost independent of damping strength.Another interesting
observation is that for the external noise driven systems, noise correlation time and
damping strength have similar roles in the dynamics. 相似文献
15.
We develop an effective low-frequency theory
of the electromagnetic field in equilibrium with thermal objects.
The aim is to compute
thermal magnetic noise spectra close to metallic
microstructures. We focus on the limit where the
material response is characterised by the
electric conductivity. At the boundary
between empty space and metallic microstructures,
a large jump occurs in the dielectric function which leads to a
partial screening of low-frequency magnetic fields generated by thermal
current fluctuations. We resolve a discrepancy between two approaches
used in the past to compute magnetic field noise spectra close to
microstructured materials. 相似文献
16.
Laurent J Mosset A Arcizet O Chevrier J Huant S Sellier H 《Physical review letters》2011,107(5):050801
Interferometric detection of mirror displacements is intrinsically limited by laser shot noise. In practice, however, it is often limited by thermal noise. Here we report on an experiment performed at the liquid helium temperature to overcome the thermal noise limitation and investigate the effect of classical laser noise on a microlever that forms a Fabry-Perot cavity with an optical fiber. The spectral noise densities show a region of "negative" contribution of the backaction noise close to the resonance frequency. We interpret this noise reduction as a coherent coupling of the microlever to the laser intensity noise. This optomechanical effect could be used to improve the detection sensitivity as discussed in proposals going beyond the standard quantum limit. 相似文献
17.
Interfacing of nerve cells and field-effect transistors is determined by current flow along the electrical resistance of the cell-chip junction. We study the thermal noise of the junction by measuring the fluctuations of extracellular voltage with a low-noise transistor. We find a spectral power density of 5 x 10(-14) V2/Hz and interpret it as Nyquist noise of the cell-chip junction with a resistance of 3 MOhm. The thermal noise allows us to elucidate the properties of cell adhesion and it sets a thermodynamical limit for the signal-to-noise ratio of neuroelectronic interfacing. 相似文献
18.
Sandeep Aashish Abhilash Padhy Sukanta Panda Arun Rana 《The European Physical Journal C - Particles and Fields》2018,78(11):887
We investigate the possibility of inflation with models of antisymmetric tensor field having minimal and nonminimal couplings to gravity. Although the minimal model does not support inflation, the nonminimal models, through the introduction of a nonminimal coupling to gravity, can give rise to stable de-Sitter solutions with a bound on the coupling parameters. The values of field and coupling parameters are sub-planckian. Slow roll analysis is performed and slow-roll parameters are defined which can give the required number of e-folds for sufficient inflation. Stability analysis has been performed for perturbations to antisymmetric field while keeping the metric unperturbed, and it is found that only the sub-horizon modes are free of ghost instability for de-Sitter space. 相似文献
19.
《Physics letters. A》1999,264(4):251-256
We have measured the displacement thermal noise of a mechanical cantilever, made of phosphor bronze, using a laser interferometer. The measured noise spectrum agrees well with an estimation based on the fluctuation–dissipation theorem with a mechanical-admittance measurement. The frequency range where we could measure the thermal noise was from 50 to 500 Hz; this range is important for the noise characterization of interferometric gravitational wave detectors. 相似文献
20.
Łuczka J 《Chaos (Woodbury, N.Y.)》2005,15(2):26107
We survey classical non-Markovian processes driven by thermal equilibrium or nonequilibrium (nonthermal) colored noise. Examples of colored noise are presented. For processes driven by thermal equilibrium noise, the fluctuation-dissipation relation holds. In consequence, the system has to be described by a generalized (integro-differential) Langevin equation with a restriction on the damping integral kernel: Its form depends on the correlation function of noise. For processes driven by nonequilibrium noise, there is no such a restriction: They are considered to be described by stochastic differential (Ito- or Langevin-type) equations with an independent noise term. For the latter, we review methods of analysis of one-dimensional systems driven by Ornstein-Uhlenbeck noise. 相似文献