What Precision Electroweak Physics Says About the SU(6)/Sp(6) Little Higgs

We study precision electroweak constraints on the close cousin of the Littlest Higgs, the SU(6)/Sp(6) model. We identify a near-oblique limit in which the heavy W' and B' decouple from the light fermions, and then calculate oblique corrections, including one-loop contributions from the extended top sector and the two Higgs doublets. We find regions of parameter space that give acceptably small precision electroweak corrections and only mild fine tuning in the Higgs potential, and also find that the mass of the lightest Higgs boson is relatively unconstrained by precision electroweak data. The fermions from the extended top sector can be as light as 1 TeV, and the W' can be as light as 1.8 TeV. We include an independent breaking scale for the B', which can still have a mass as low as a few hundred GeV.Comment: 52 pages, 16 figure

Bubble dynamics in pool boiling of nanofluids

Bubble dynamics of pool boiling of nanofluids has been experimentally investigated. The boiling surface was prepared with an average surface roughness of 120 nm. Alumina Oxide- water based nanofluids at a constant concentration of 0.05 wt. % have been used in this investigation. The bubble growth rate, bubble departure diameter and departure frequency have been observed using high speed imaging during pool boiling of pure water and nanofluids at a wall superheat of 104.4 ºC. Number of nucleation sites was activated in the case of nanofluid against one site for pure water. The bubble diameter observed in the case of nanofluids was about 60 % smaller than that observed for pure water. Nanofluid’s bubble departure frequency reached 500 Hz while the bubble frequency observed in the case of pure water was about 23 Hz. In addition, the bubble growth rate showed dependence on the type of working fluid used.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Bubble dynamics under an impinging planar water jet

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The limiting factor in many industries is the maximum operating temperature and/or the maximum heat flux to be dissipated from the surface. Liquid Jet Impinging Cooling (LJIC) is one of the most effective cooling means because of its high heat transfer coefficient. LJIC is extensively used in steel quenching, electronic chips cooling and emergency rapid core cooling in nuclear reactors. Though, the surface heat flux has no straight forward formula. The present study adapts the mechanistic modeling approach to quantify the surface heat flux under different conditions. The mechanistic model assumes that the heat is transferred from the surface through multiple mechanisms, namely: boiling, forced convection and transient conduction. The total wall heat flux is calculated as the algebraic sum of these different heat flux components. The boiling heat transfer component depends on bubbles behaviour on the surface (bubble dynamics). Bubble growth rate, departure diameter, release frequency and number of bubbles on the surface are the major bubble dynamics parameters that are affected by the jet. This paper presents the result of an experimental investigation of bubble dynamics under a planar water jet. The experimental data are collected using high speed imaging of the boiling process at different degrees of superheating. Results reported here are for a 0.85 m/s jet. The jet was found to suppress nucleation close to the impinging zone and deform growing bubble from the spherical shaper. Away from stagnation, bubble diameter was found to depend on the square root of growth time, i.e. D~tg^1/2cf201

Null energy condition and superluminal propagation

We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimicking $\dot H>0$ in scalar tensor theories of gravity.Comment: 46 pages, 6 figure

Numerical study of the effect of liquid sloshing inside TLD on suppression of gust wind-induced vibration in high rise buildings

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Needless to say that the use of TLD in damping of the light scale vibration in due to wind excitation as well as the large scale excitation on offshore platforms exhibits an effective dynamic absorber. One of the prime importance of using TLD as an effective absorber coupled with structure is to impart the effect of fatigue stresses accompanied with the repeated excitation loads. The serviceability of the high rise buildings and the steel towers is another important application of using TLD to suppress the building acceleration and realize the comfort and healthy conditions. The full scale measurements of the structure dynamic response exhibits an effective method for the validation of the structure design procedure and emphasize the accuracy of the numerical models suggested predicting the structure dynamic response. The current model behaves as a NSE model accurately predict the sloshing fluid motion inside TLD and handles the moving free surface by using the (VOF) method. The current model use the continuum surface force model CSF to model the discontinuity accompanied with wave breaking inside TLD. The numerical model used in this paper predicts the interaction between the structure dynamic response and highlights the damping effect of TLD groups allocated at different floors of tall buildings. The current model suggests a new criterion to detect the wave breaking and focus attention on the effect of wave breaking on the impact force in due to the sloshing fluid motion inside TLD for a wide range of excitation frequencies. The numerical model used in this paper handles the interaction between the structure dynamic response and the damping effect of TLD groups allocated at different floors of the tall building. The model was validated by a direct comparison with the full scale measurements of one of the high rise buildings. The direct comparison shows a good agreement proves that the current numerical model is a powerful tool used assess the damping effect of TLD on structure dynamic response.cf201

On wave breaking in tuned liquid dampers

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Tuned Liquid Dampers (TLDs) are passive damping devices used to damp vibration due to wind in tall buildings and due to sea waves in offshore platforms. This paper pre-sents numerical results of wave breaking in TLDs obtained using a numerical model developed in-house. The model solves the full form of Navier-Stokes equations for viscous liquid sloshing and handles the moving free surface by using the volume of fluid method (VOF). Some of the previous numerical models invoke a two-phase flow model in con-junction with the VOF method to simulate the wave trans-formation and wave breaking in shallow water. However, these two-phase flow models give no account to the effect of body force on the free surface. The current model uses the continuum surface force model (CSF) which models the discontinuity accompanied with wave breaking as a con-tinuous transition where fluid properties such as density vary smoothly from one fluid to another. Numerous experi-mental studies reveal that the impulse pressure exerted on the tank walls varies in a similar nature as that of the applied excitation. Accordingly, the current numerical model sug-gests new formulae for the pressure at the left and right TLD walls. The present numerical results are in good agreement with experimental data. The current model is able to accu-rately detect surface wave breaking at various excitation frequencies.dc201

Experimental investigation of re-wetting of hot horizontal tubes

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Re-wetting of a hot dry surface is the establishment of direct contact between the surface and a liquid at a lower temperature. Re-wetting heat transfer is characterized by a large increase in heat transfer from the surface and occurs when a vapor film existing between the dry surface and the liquid is destabilized. Study of re-wetting heat transfer is very important in nuclear reactor safety for limiting the extent of core damage during the early stages of severe accidents after loss of coolant accidents LOCA and is essential for predicting the rate at which the coolant cools an overheated core. Surface re-wetting is established by the formation of a wet patch on the hot dry surface which then grows in size to cover the entire surface. The leading edge of the wet patch is called the re-wetting front and consists of transition and nucleate boiling heat transfer regions. The aim of this study is to introduce and study two important variables related to the re-wetting front as it moves on hot horizontal tubes cooled by water jet impingement. These variables are: the rebound phenomenon of the re-wetting front and the width of the re-wetting front. Experimental observations of this study showed that the re-wetting front could rebound a small distance just after the formation of the wet patch due to rapid heat conduction in the solid towards the wet patch. The rebound distance was found to increase by decreasing water temperature and the velocity of the jet. The width of the re-wetting front was found to increase by increasing water temperature and decreasing the initial surface temperature. As the solid thermal conductivity increases, this width was found to increase.mp201

Cosmological Effects of Radion Oscillations

We show that the redshift of pressureless matter density due to the expansion of the universe generically induces small oscillations in the stabilized radius of extra dimensions (the radion field). The frequency of these oscillations is proportional to the mass of the radion and can have interesting cosmological consequences. For very low radion masses $m_b$ ($m_b\sim10-100 H_0\simeq10^{-32} eV$) these low frequency oscillations lead to oscillations in the expansion rate of the universe. The occurrence of acceleration periods could naturally lead to a resolution of the coincidence problem, without need of dark energy. Even though this scenario for low radion mass is consistent with several observational tests it has difficulty to meet fifth force constraints. If viewed as an effective Brans-Dicke theory it predicts $\omega=-1+\frac{1}{D}$ ($D$ is the number of extra dimensions), while experiments on scales larger than $1mm$ imply $\omega>2500$. By deriving the generalized Newtonian potential corresponding to a massive toroidally compact radion we demonstrate that Newtonian gravity is modified only on scales smaller than $m_b^{-1}$. Thus, these constraints do not apply for $m_b>10^{-3} eV$ (high frequency oscillations) corresponding to scales less than the current experiments ($0.3mm$). Even though these high frequency oscillations can not resolve the coincidence problem they provide a natural mechanism for dark matter generation. This type of dark matter has many similarities with the axion.Comment: Accepted in Phys. Rev. D. Clarifying comments added in the text and some additional references include

The Bulk RS KK-gluon at the LHC

We study the possibility of discovering and measuring the properties of the lightest Kaluza-Klein excitation of the gluon in a Randall-Sundrum scenario where the Standard Model matter and gauge fields propagate in the bulk. The KK-gluon decays primarily into top quarks. We discuss how to use the $t \bar{t}$ final states to discover and probe the properties of the KK-gluon. Identification of highly energetic tops is crucial for this analysis. We show that conventional identification methods relying on well separated decay products will not work for heavy resonances but suggest alternative methods for top identification for energetic tops. We find, conservatively, that resonances with masses less than 5 TeV can be discovered if the algorithm to identify high $p_T$ tops can reject the QCD background by a factor of 10. We also find that for similar or lighter masses the spin can be determined and for lighter masses the chirality of the coupling to $t\bar t$ can be measured. Since the energetic top pair final state is a generic signature for a large class of new physics as the top quark presumably couples most strongly to the electroweak symmetry breaking sector, the methods we have outlined to study the properties of the KK-gluon should also be important in other scenarios.Comment: 21 pages, 13 figure

Emergent Electroweak Symmetry Breaking with Composite W, Z Bosons

We present a model of electroweak symmetry breaking in a warped extra dimension where electroweak symmetry is broken at the UV (or Planck) scale. An underlying conformal symmetry is broken at the IR (or TeV) scale generating masses for the electroweak gauge bosons without invoking a Higgs mechanism. By the AdS/CFT correspondence the W,Z bosons are identified as composite states of a strongly-coupled gauge theory, suggesting that electroweak symmetry breaking is an emergent phenomenon at the IR scale. The model satisfies electroweak precision tests with reasonable fits to the S and T parameter. In particular the T parameter is sufficiently suppressed since the model naturally admits a custodial SU(2) symmetry. The composite nature of the W,Z-bosons provide a novel possibility of unitarizing WW scattering via form factor suppression. Constraints from LEP and the Tevatron as well as discovery opportunities at the LHC are discussed for these composite electroweak gauge bosons.Comment: 39 pages, 4 figure