Vacuum Value Research Articles

More about the $$B$$ B and $$D$$ D mesons in nuclear matter

We calculate the shifts in decay constants of the pseudoscalar $$B$$ and $$D$$ mesons in nuclear medium in the frame work of QCD sum rules. We write those shifts in terms of the $$B$$ – $$N$$ and $$D$$ – $$N$$ scattering lengths and an extra phenomenological parameter entered to calculations. Computing an appreciate forward scattering correlation function, we derive the QCD sum rules for the $$B$$ – $$N$$ and $$D$$ – $$N$$ scattering lengths and the extra phenomenological parameter in terms of various operators in nuclear medium. We numerically find the values of the shifts in the decay constants compared to their vacuum values. Using the sum rules obtained, we also determine the shifts in the masses of these particles due to nuclear matter and compare the results obtained with the previous predictions in the literature.

Standard Model with a real singlet scalar and inflation

We study the post-inflationary dynamics of the Standard Model Higgs and a real singlet scalar s, coupled together through a renormalizable coupling λshh2s2, in a Z2 symmetric model that may explain the observed dark matter abundance and/or the origin of baryon asymmetry. The initial values for the Higgs and s condensates are given by inflationary fluctuations, and we follow their dissipation and relaxation to the low energy vacua. We find that both the lowest order perturbative and the non-perturbative decays are blocked by thermal effects and large background fields and that the condensates decay by two-loop thermal effects. Assuming instant reheating at T=1016 GeV, the characteristic temperature for the Higgs condensate thermalization is found to be Th ∼ 1014 GeV, whereas s thermalizes typically around Ts ∼ 106 GeV. By that time, the amplitude of the singlet is driven very close to the vacuum value by the expansion of the universe, unless the portal coupling takes a value λsh≲ 10-7 and the singlet s never thermalizes. With these values of the coupling, it is possible to slowly produce a sizeable fraction of the observed dark matter abundance via singlet condensate fragmentation and thermal Higgs scattering. Physics also below the electroweak scale can therefore be affected by the non-vacuum initial conditions generated by inflation.

String theoretic QCD axions in the light of PLANCK and BICEP2

The QCD axion solving the strong CP problem may originate from antisymmetric tensor gauge fields in compactified string theory, with a decay constant around the GUT scale. Such possibility appears to be ruled out now by the detection of tensor modes by BICEP2 and the PLANCK constraints on isocurvature density perturbations. A more interesting and still viable possibility is that the string theoretic QCD axion is charged under an anomalous U(1)_A gauge symmetry. In such case, the axion decay constant can be much lower than the GUT scale if moduli are stabilized near the point of vanishing Fayet-Illiopoulos term, and U(1)_A-charged matter fields get a vacuum value far below the GUT scale due to a tachyonic SUSY breaking scalar mass. We examine the symmetry breaking pattern of such models during the inflationary epoch with the Hubble expansion rate 10^{14} GeV, and identify the range of the QCD axion decay constant, as well as the corresponding relic axion abundance, consistent with known cosmological constraints. In addition to the case that the PQ symmetry is restored during inflation, there are other viable scenarios, including that the PQ symmetry is broken during inflation at high scales around 10^{16}-10^{17} GeV due to a large Hubble-induced tachyonic scalar mass from the U(1)_A D-term, while the present axion scale is in the range 10^{9}-5\times 10^{13} GeV, where the present value larger than 10^{12} GeV requires a fine-tuning of the axion misalignment angle. We also discuss the implications of our results for the size of SUSY breaking soft masses.

Relationship of Pressure and Plasma Temperature in Plasma DC Glow Discharge

The DC glow discharge of nitrogen gas was carried out by 5 kV DC power supply, which was used to bias voltage between two parallel plate electrodes in the cylindrical glass tube chamber. The distance between two parallel plate electrodes was about 37.5 cm. The voltage was applied on these electrodes between 800 V to 1400 V. The nitrogen pressure in the cylindrical glass tube chamber was controlled by rotary pump and vacuum value. Optical Emission Spectroscopy (OES) was used to investigate the local emissivity of nitrogen glow discharge in the range between 200 and 1,100 nm. The spatial distribution of reactive species was measured at different nitrogen pressures from 0.15-1.90 mbar. These measurements were obtained to analyze the electron temperature. The effect of different nitrogen pressures was studied on the electron temperature and the configuration of nitrogen plasma. In the result, it was found that the plasma column increased with increasing the nitrogen pressure. The electron temperature was less than 0.8 eV.

Effect of the settings of two automatic cluster removers (ACRs) on the milking efficiency of Manchega ewes

The implementation of automatic vacuum cutting devices (AVCDs, component of the ACRs, automatic cluster removers) represents one of the most recent advances in small ruminant milking machines. However, there is a lack of scientific studies regarding optimal settings (milk flow threshold, MF, and delay time, DT) for the milking of Manchega ewes. The aim of this study was to assess the effect of different combinations of operating parameters of two AVCDs (LactoFlow®-Dematron® of GeaFarm Technologies® and SG®-mm25® of DeLaval®) on milking efficiency (milking time and milk fractioning), milking routine (cluster falls and double cluster attachment) and mean vacuum drops. Two tests were performed including several latin square design experiments. Regarding LactoFlow®-Dematron® installed in a low-line milking machine, four MF (100, 150, 200 and 250g/min) were combined with three DT (10, 15 and 20s) employing 45 ewes on a research farm and regarding SG®-mm25® installed in high-line milking machine, two MF (150 and 200g/min) were combined with three DT (10, 15 and 20s) employing 54 ewes on a commercial farm. According to the results, regarding Dematron®-Lactoflow®, it was appreciable that the employment of MF 100g/min increased milking duration without improving the milk fractioning and the employment of MF 250g/min did not reduce milking duration. The minimum differences between MF 150 and 200g/min showed in this test suggest that these levels would be located within the optimal setting of this AVCD. On the other hand, regarding SG®-mm25®, two strategies could be considered, the use of MF 150g/min combined with high DT to extract the maximum amount of milk or the use of MF 200g/min combined with short DT to optimize the time employed. Regarding milking routine, no differences were found in any of the test. The increase of both MF and DT showed higher values of mean vacuum drops in the two tests performed.Further studies are needed to study how AVCD affects the milking time of the total herd, production and composition of the milk and the sanitary status of the mammary gland of Manchega breed ewes.

Electron-induced secondary electron emission coefficient of lithium, tungsten and stainless steel surfaces exposed to low-pressure plasmas

The secondary electron emission (SEE) coefficient by electron impact of Li, W and stainless steel (SS) surfaces exposed to a glow discharge is evaluated and analyzed in the energy range of Ee<200eV. While the values of the SEE coefficient for SS and W show a small increase with respect to their vacuum value, an enhancement of this parameter up to a factor of 6 has been deduced for clean Li surfaces. Experiments with different plasma gas discharges (He, Ar and H2) are undertaken in order to address the possible mechanisms related to such enhancement. No major effect of the bombarding ion mass or incident electron flux is observed. The implications of these findings on the use of Li as a plasma-facing component in fusion devices are addressed.

Transient response analysis of a steel beam with vacuum packed particles

In this paper the method of semi-active damping of vibrations is presented. Free vibrations of a cantilever steel beam encapsulated in a sleeve, filled with the granular material are investigated. Various values of the partial vacuum generated in the granular structure allow to control the global dissipative properties of the discussed system. The loose grains encapsulated in the hermetic, polyvinyl chloride (PVC) envelope transform into a rigid, viscoplastic body as the jamming mechanism occurs when the underpressure is generated. Such phenomenon enables original strategies for semi-active damping. A detailed discussion related to the experimental results concerning the amplitude of vibration, damping, stiffness, and frequency of the continuous granular beam system is provided. The simplified Finite Element Model succeeded in describing the dynamic response of the structure.

Thermal properties of and tensor mesons using QCD sum rules

We investigate the masses and decay constants of the heavy–light and tensor mesons in the framework of thermal QCD sum rules. Taking into account the additional operators arising at finite temperature, we evaluate the Wilson expansion for the two-point correlation function associated with these mesons. We observe that the values of the masses and decay constants decrease considerably at near to the critical temperature. The decay constants attain roughly to 25% of their values in vacuum, while the masses decrease about 39% and 37% in and channels, respectively.

N‐type in‐situ doping effect on vapour‐liquid‐solid silicon nanowire properties for gas sensing applications

AbstractN‐type in‐situ doped SiNWs based resistors are fabricated and used as gas (ammonia) sensors. SiNWs are prepared by vapour‐liquid‐solid method (VLS) using gold as catalyst. In‐situ doping level is adjusted by varying the phosphine to silane mole ratio. Because SiNWs can act as sensitive units specific design is developed to allow large sensing areas, following a process fabrication compatible with a mass production planar layout. SiNWs doping effect on ammonia detection is carried out under controlled ammonia/nitrogen mixture varying from 2 ppm to 700 ppm. Results highlight that the relative response, Sg=(I0‐Ig)/I0, where I0 and Ig are the current values in vacuum and reactive ambient respectively, follows a linear behaviour. The relative sensitivity, (S=ΔSg/Δ[NH3]) decreases, whereas the sensitivity (SxI0) increases with the increase of the VLS SiNWs doping level. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dimuon production from in-medium rho decays from QCD sum rules

We compute the dimuon-excess invariant mass distribution at the rho-meson peak in the context of relativistic heavy-ion collisions at SPS energies. The temperature, T, and chemical potential, mu, dependent parameters describing the rho-meson --its width, mass and leptonic decay constant-- are determined from finite energy QCD sum rules. Results show that the rho-meson width increases whereas its mass and leptonic decay constant decrease near the (chemical potential-dependent) critical temperature T_c(mu) for chiral symmetry restoration/quark-gluon deconfinement. As a consequence, starting from T_c(mu), for a short lived cooling the main effect is a broadening of the dimuon distribution. However, when the evolution brings the system to a lower freeze-out temperature, with the rho-meson parameters approaching their vacuum values, the dimuon distribution shows a broad peak centered at the vacuum rho-meson mass. For even lower freeze-out temperatures the peak becomes less prominent since the thermal phase space factor suppresses the distribution for larger values of the invariant dimuon mass, given that the average temperature is smaller. The dimuon distribution exhibits a non-trivial behavior with mu. For small mu values the distribution broadens with increasing mu becoming a bit steeper at low invariant masses for larger values of mu. Our results are in very good agreement with data from the NA60 Collaboration.

Analysis on Chilled Water Spraying through Extraction Opening in Condenser to Enhance Extraction Effect of Vacuum Pump

Non condensable gas (air) accumulating in the condenser will reduce heat transfer coefficient of condense and vacuum value, Reducing of condenser vacuum value will lower turbine efficiency. Chilled water spraying is adopted to cool down the steam before it is extracted through extraction opening in condenser so as to enhance extraction effect of vacuum pump. This paper gives analysis on chilled water spraying through extraction opening. Mathematic model of selected controlling volume near extraction opening is given. Maximum amount of spraying and its relationship with vacuum value and increment of extraction rate are also proposed.

Theoretical study on the static and dynamic first-order hyperpolarisabilities of adenine tautomers

Static and dynamic electronic and vibrational first-order hyperpolarisabilities (β) of the lowest energy neutral adenine tautomers (amine forms A7 and A9) were obtained in gaseous and aqueous phases by using Hartree–Fock, Møller–Plesset second-order and fourth-order perturbation theory (MP2 and MP4-SDQ) and conventional and long-range corrected density functional theory methods with the Dunning's correlation-consistent cc-pVDZ, aug-cc-pVDZ, aug-cc-pVTZ and d-aug-cc-pVDZ basis sets. Frequency-dependent properties were calculated at the characteristic wavelength of the Nd:YAG laser (1064 nm) for the second harmonic generation and electro-optical Pockels effect nonlinear optical processes. Solvent effects were introduced under the polarised continuum model approximation. The electronic βe values of the investigated isomers are noticeably affected by the theoretical level, basis set and solvation. In vacuum, the static and dynamic βe values of A9 are greater than the corresponding data of A7, whereas the contribution of the solvent significantly enhances the hyperpolarisabilities of the A7 tautomer, resulting in βe(A9)/βe(A7) ratios between 0.5 and 0.6. The vibrational hyperpolarisabilities of the adenine tautomers are quite close to each other.

Dense hadronic matter in holographic QCD

We provide a method to study hadronic matter at finite density in the context of the Sakai-Sugimoto model. We introduce the baryon chemical potential through the external U(1) v gauge field in the induced (DBI plus CS) action on the D8-probe-brane, where baryons are skyrmions. Vector dominance is manifest at finite density. We derive the effect of the baryon density on the energy density, and on the dispersion relations of pions and vector mesons at large N c . The energy density asymptotes are constant at large density, suggesting that dense matter at large N c freezes, with the pion velocity dropping to zero. Holographic dense matter enforces exactly the tenets of vector dominance and efficiently screens vector mesons. At the freezing point, the ρ — ππ coupling vanishes with a finite rho mass of about 20% its vacuum value.

Growth of one-dimensional vertically aligned carbon nanostructures on SiC—Catalyst effect

Application of catalyst on SiC wafer resulted in the formation of one-dimensional (1D) vertically aligned carbon nanostructures at low temperature and vacuum values (compared to SiC decomposition) without extra carbon supply into the system. Resulting nanostructures were characterized using scanning electron microscopy and Raman spectroscopy. The effect of catalyst amount is discussed and a mechanism for the 1D carbon nanostructure formation through SiC decomposition in the presence of catalyst is proposed.

Thermodynamics and phase transition of theO(N)model from the two-loopΦ-derivable approximation

We discuss the thermodynamics of the O(N) model across the corresponding phase transition using the two-loop Phi-derivable approximation of the effective potential and compare our results to those obtained in the literature within the Hartree-Fock approximation. In particular, we find that in the chiral limit the transition is of the second order, whereas it was found to be of the first order in the Hartree-Fock case. These features are manifest at the level of the thermodynamical observables. We also compute the thermal sigma and pion masses from the curvature of the effective potential. In the chiral limit, this guarantees that the Goldstone's theorem is obeyed in the broken phase. A realistic parametrization of the model in the N=4 case, based on the vacuum values of the curvature masses, shows that a sigma mass of around 450 MeV can be obtained. The equations are renormalized after extending our previous results for the N=1 case by means of the general procedure described in [J. Berges et al., Annals Phys. 320, 344-398 (2005)]. When restricted to the Hartree-Fock approximation, our approach reveals that certain problems raised in the literature concerning the renormalization are completely lifted. Finally, we introduce a new type of Phi-derivable approximation in which the gap equation is not solved at the same level of accuracy as the accuracy at which the potential is computed. We discuss the consistency and applicability of these types of "hybrid" approximations and illustrate them in the two-loop case by showing that the corresponding effective potential is renormalizable and that the transition remains of the second order.

Spontaneous emission in the presence of a spherical plasmonic metamaterial

We investigate the spontaneous emission of a two-level atom placed in the vicinities of a plasmonic cloak composed of a coated sphere. In the dipole approximation, we show that the spontaneous emission rate can be reduced to its vacuum value provided the atomic emission frequency lies within the plasmonic cloak frequency operation range. Considering the current status of plasmonic cloaking devices, this condition may be fulfilled for many atomic species so that we argue that atoms with a sufficiently strong transition can be used as quantum, local probes for the efficiency of plasmonic cloaks.

Mass shift of σ-meson in nuclear matter

The propagation of σ-meson in nuclear matter is studied in the Walecka model, by assuming that the sigma couples to a pair of nucleon–antinucleon states and to particle–hole states. The in-medium effect of σ–ω mixing is also studied. For completeness, the coupling of sigma to two virtual pions was also considered. It is found that the σ-meson mass decreases with respect to its value in vacuum and that the contribution of the σ–ω mixing effect on the mass shift is relatively small.

Fluctuation properties of acoustic phonons generated by ultrafast optical excitation of a quantum dot

We study theoretically the fluctuation properties of acoustic phonons created in a semiconductor quantum dot after ultrafast optical excitation. An excitation with a single ultrafast pulse creates an exciton confined to the quantum dot, which is coupled to longitudinal acoustic phonons. This leads to the formation of a polaron in the quantum dot accompanied by the emission of a phonon wave packet. We show that the fluctuations of the lattice displacement associated with the wave packet after a single laser pulse excitation in resonance with the exciton transition are always larger than their respective vacuum values. Manipulating the exciton with a second pulse can result in a reduction of the fluctuations below their vacuum limit, which means that the phonons are squeezed. We show that the squeezing properties of the wave packet strongly depend on the relative phase and the time delay between the two laser pulses.

Topological ghosts and cosmological structure formation

We consider dynamics of space-time volume-filling form fields with ``wrong sign'' kinetic terms, such as in so-called type-II* string theories. Locally, these form fields are just additive renormalizations of the cosmological constant. They have no fluctuating degrees of freedom. However, once the fields are coupled to membranes charged under them, their configurations are unstable: by a process analogous to Schwinger pair production the field space-filling flux increases. This reduces the cosmological constant and preserves the null energy condition, since the processes that can violate it by reducing the form flux are very suppressed. The increase of the form flux implies that as time goes on the probability for further membrane nucleation increases, in contrast to the usual case where the field approaches its vacuum value and ceases to induce further transitions. Thus, in such models spaces with tiny positive vacuum energy are ultimately unstable, but the instability may be slow and localized. In a cosmological setting, this instability can enhance black hole rate formation, by locally making the vacuum energy negative at late times, which constrains the scales controlling membrane dynamics, and may even collapse a large region of the visible Universe.

Electric and magnetic screenings of gluons in a model with a dimension-2 gluon condensate

Electric and magnetic screenings of thermal gluons are studied using the background expansion method in a gluodynamic model with a gauge invariant dimension-2 gluon condensate at zero momentum. At low temperature, the electric and magnetic gluons are degenerate. With the increase of temperature, it is found that the electric and magnetic gluons start to split at a certain temperature T0. The electric screening mass changes rapidly with temperature when T > T0, and the Polyakov loop expectation value rises sharply around T0 from zero in the vacuum to a value around 0.8 at a high temperature. This suggests that the color electric deconfinement phase transition is driven by electric gluons. It is also observed that the magnetic screening mass remains almost the same as its vacuum value, which manifests that the magnetic gluons remain confined. Both the screening masses and the Polyakov loop results are qualitatively in agreement with the Lattice calculations.