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Electron energy spectrum and maximum disruption angle under multi-photon beamstrahlung

Description: The final electron energy spectrum under multi-photon beamstrahlung process is derived analytically in the classical and the intermediate regimes. The maximum disruption angle from the low energy tail of the spectrum is also estimated. The results are then applied to the TLC and the CLIC parameters. 6 refs., 1 fig., 1 tab.
Date: March 1, 1989
Creator: Yokoya, Kaoru & Chen, Pisin
Partner: UNT Libraries Government Documents Department

Depolarization due to beam-beam interaction in electron-positron linear colliders

Description: We investigate two major mechanisms which induce depolarization of electron beams during beam-beam interaction in linear colliders. These are the classical spin precession under the collective field of the oncoming beam, and the spin-flip effect from beamstrahlung. Analytic formulas are derived for estimating these depolarization effects. As examples, we estimate the depolarization in the Stanford Linear Collider (SLC) and a possible future TeV linear collider (TLC). The effects are found to be negligibly small for SLC and not very large for TLC. 7 refs., 1 fig.
Date: September 1, 1988
Creator: Yokoya, Kaoru & Chen, Pisin
Partner: UNT Libraries Government Documents Department

Final focus plasma lenses in linear colliders

Description: In this paper we analyze the optics of a high energy beam which is focused by its own wake-fields in an overdense plasma. We calculate the effects of lens aberration on the focusing strength of the lens and on the dilution of the beam's phase space density. From this we derive the minimum spot size achievable using a cylindrically symmetric bi-Gaussian beam and, after inclusion of the beam-beam disruption effect, the luminosity enhancement that can be gained in principle. We estimate the luminosity enhancement in the case of SLC design parameters and discuss limitations and possible improvements in plasma lens performance. Motivated by the need to reduce the background event rate due to beam-ion collisions, we discuss the optics of the underdense plasma lens and introduce the concept of bootstrap disruption. Possible use of the underdense plasma lens in a TLC-type collider is examined. 14 refs., 5 figs., 1 tab.
Date: October 11, 1988
Creator: Rosenzweig, J.B. & Chen, Pisin
Partner: UNT Libraries Government Documents Department

Dark Energy and the Hierarchy Problem

Description: The well-known hierarchy between the Planck scale (>> 1019GeV) and the TeV scale, namely a ratio of {approx} 10{sup 16} between the two, is coincidentally repeated in a inverted order between the TeV scale and the dark energy scale at {approx} 10{sup -3} eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the dark energy. For the ADD model we found that our notion is sensible only if the number of extra dimension n = 2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass-shifts at the TeV level, the zero-mode contribution to Casimir energy is overshadowed.
Date: December 6, 2006
Creator: Chen, Pisin
Partner: UNT Libraries Government Documents Department

Differential luminosity under beamstrahlung

Description: For the next generation of e{sup +}e{sup {minus}} linear colliders in the TeV range, the energy loss due to beamstrahlung during the collision of the e{sup +}e{sup {minus}} beams is expected to be substantial. One consequence is that the center-of-mass energy between the colliding particles can be largely degraded from the designed value. The knowledge on the differential luminosity as a function of the center-of-mass energy is essential for particle physics analysis on the interesting events. In this paper we derive an analytic formula for such a differential luminosity which agrees very well with computer simulations. A major characteristic of this formula is discussed. 5 refs., 1 fig.
Date: May 1, 1991
Creator: Chen, Pisin.
Partner: UNT Libraries Government Documents Department

Instability of compensated beam-beam collisions

Description: The beam-beam disruption phenomena in linear colliders are increasingly seen as a source of serious problems for these machines. A plasma compensation scheme, in which the motion of the plasma electrons in the presence of the colliding beams provides neutralizing charge and current densities, has been proposed and studied. But natural alternative to this scheme is to consider the overlapping of nearly identical high energy e/sup +/ and e/sup /minus// bunches, and the collision of two such pairs - in other words, collision of two opposing relativistic positronium plasmas. It should be noticed that while the luminosity for all collisions is increased by a factor of four in this scheme, the event rate for e/sup +/e/sup /minus// collisions is only increased by a factor of two. The other factor of two corresponds to the addition of e/sup +/e/sup +/ and e/sup /minus//e/sup /minus// collisions to the interaction point. This beam compensation scheme, which has been examined through computer simulation by Balakin and Solyak in the Soviet Union, promises full neutralization of beam charges and currents. These numerical investigations have shown that plasma instabilities exist in this nominally neutral system. Although the implementation of this idea seems technically daunting, the potential benefits (beamstrahlung and disruption suppression, relaxation of final focus system constraints) are such that we should consider the physics of these collisions further. In the remainder of this paper, we theoretically analyze the issues of stability and bunch parameter tolerances in this scheme. 11 refs.
Date: February 13, 1989
Creator: Rosenzweig, J.B.; Autin, B. & Chen, Pisin
Partner: UNT Libraries Government Documents Department

Plasma Suppression of Large Scale Structure Formation in the Universe

Description: We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce a residual long-range electrostatic potential which, working together with the baryon thermal pressure, would counter the gravitational collapse. As a result the effective Jean's length, {tilde {lambda}}{sub J}, is increased by a factor, {tilde {lambda}}{sub J}/{lambda}{sub J} = {radical}8/5, relative to the conventional one. For scales smaller than the effective Jean's scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect depend on the starting time and the initial temperature of reionization, but roughly lie in the range 0.5hMpc{sup -1} < k, which corresponds to the region of the Lyman-{alpha} forest from the inter-galactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach 1 - ({Omega}{sub dm}/{Omega}{sub m}){sup 2} {approx} 1 -(5/6){sup 2} {approx} 30%.
Date: December 10, 2007
Creator: Chen, Pisin & Lai, Kwang-Chang
Partner: UNT Libraries Government Documents Department

Cosmological Constant as a Manifestation of the Hierarchy

Description: There has been the suggestion that the cosmological constant as implied by the dark energy is related to the well-known hierarchy between the Planck scale, M{sub PI}, and the Standard Model scale, M{sub SM}. Here we further propose that the same framework that addresses this hierarchy problem must also address the smallness problem of the cosmological constant. Specifically, we investigate the minimal supersymmetric (SUSY) extension of the Randall-Sundrum model where SUSY-breaking is induced on the TeV brane and transmitted into the bulk. We show that the Casimir energy density of the system indeed conforms with the observed dark energy scale.
Date: December 21, 2007
Creator: Chen, Pisin & Gu, Je-An
Partner: UNT Libraries Government Documents Department


Description: Collisions of short, intense laser pulses with electron beams have recently been proposed for various purposes, such as high-quality, Compton-Backscattered X-ray sources (CBX), or coherent pair production positron sources for future e{sup +}e{sup {minus}} Linear Colliders. For such intense laser fields, few-photon perturbative treatments do not suffice, and nonperturbative effects in the fields must be modeled. These effects have, until recently, only been modeled within the ''local plane wave'', or Volkov, approximation, in which ponderomotive (i.e. laser intensity gradient) effects are ignored. A systematic quantum treatment of the ''post-Volkov'' effects occurring in such collisions has recently been initiated by Ben-Menahem. In the present paper, we use the results of to render a simplified treatment of the leading ponderomotive corrections to electron trajectories during the electron-laser collision, and estimate the ramifications for CBX sources which utilize such collisions. We also apply to the CBX case some recently derived estimates of three non-ponderomotive effects: two body collisions in the laser-induced shower; EM self-forces of this shower; and back-reaction of linac-laser collisions upon the laser fields. All three effects are shown to be negligible for the numerical examples considered here.
Date: September 1, 1999
Creator: Chen, Pisin
Partner: UNT Libraries Government Documents Department

Plasma focusing and diagnosis of high energy particle beams

Description: Various novel concepts of focusing and diagnosis of high energy charged particle beams, based on the interaction between the relativistic particle beam and the plasma, are reviewed. This includes overdense thin plasma lenses, and (underdense) adiabatic plasma lens, and two beam size monitor concepts. In addition, we introduce another mechanism for measuring flat beams based on the impulse received by heavy ions in an underdense plasma. Theoretical investigations show promise of focusing and diagnosing beams down to sizes where conventional methods are not possible to provide. 21 refs.
Date: September 1, 1990
Creator: Chen, Pisin.
Partner: UNT Libraries Government Documents Department

Coherent pair creation from beam-beam interaction

Description: It has recently been recognized that in future linear colliders, there is a finite probability that the beamstrahlung photons will turn into e{sup +}e{sup {minus}} pairs induced by the same beam-beam field, and this would potentially cause background problems. In this paper, we first review the probability of such a coherent pair creation process. It is seen that the constraint on the beamstrahlung parameter, {Upsilon}, is tight of these coherent pairs to be totally suppressed. We then point out that there exists a minimum energy for the pair-created particles, which scales as {approximately}1/5{Upsilon}. When combining this condition with the deflection angle for the low-energy particles, the constraint on the allowable {Upsilon} value is much relaxed. Finally, we calculate the effective cross section for producing the weak bosons by the low-energy e{sup +}e{sup {minus}} pairs. It is shown that these cross sections are substantial for {Upsilon} > 1. We suggest that this effect can help to autoscan the particle spectrum in the high energy frontier. 10 refs., 2 figs.
Date: September 1, 1989
Creator: Chen, Pisin.
Partner: UNT Libraries Government Documents Department

Summary of the Physics Opportunities Working Group

Description: The Physics Opportunities Working Group was convened with the rather general mandate to explore physic opportunities that may arise as new accelerator technologies and facilities come into play. Five topics were considered during the workshop: QED at critical field strength, novel positron sources, crystal accelerators, suppression of beamstrahlung, and muon colliders. Of particular interest was the sense that a high energy muon collider might be technically feasible and certainly deserves serious study.
Date: December 1, 1992
Creator: Chen, Pisin & McDonald, K. T.
Partner: UNT Libraries Government Documents Department

The Landau-Pomeranchuk-Migdal effect and suppression of beamstrahlung and bremsstrahlung in linear colliders

Description: It is well known that beamstrahlung and bremsstrahlung take place over a finite formation zone distance. If something disturbs the electron during this time, the emission can be suppressed. In this paper, we examine the Landau-Pomeranchuk-Migdal (LPM) effect and other LPM-like effects, such as the longitudinal density (di- electric) suppression and EM field suppression of beamstrahlungand bremsstrahlungin e{sup +}e{sup -} linear colliders. We show that while the LPM effect and the density effect are not sufficient in suppressing these radiations, the strong EM field of the opposing beam does help to suppress bremsstrahlung.
Date: December 1, 1992
Creator: Chen, Pisin & Klein, S.
Partner: UNT Libraries Government Documents Department

A Possible Solution to the Smallness Problem of Dark Energy

Description: The smallness of the dark energy density has been recognized as the most crucial difficulty in understanding dark energy and also one of the most important questions in the new century. In a recent paper[1], we proposed a new dark energy model in which the smallness of the cosmological constant is naturally achieved by invoking the Casimir energy in a supersymmetry-breaking brane-world. In this paper we review the basic notions of this model. Various implications, perspectives, and subtleties of this model are briefly discussed.
Date: July 8, 2005
Creator: Chen, Pisin; /SLAC; Gu, Je-An & /Taiwan, Natl. Taiwan U.
Partner: UNT Libraries Government Documents Department

A Possible Connection Between Dark Energy And the Hierarchy

Description: Recently it was suggested that the dark energy maybe related to the well-known hierarchy between the Planck scale ({approx} 10{sup 19} GeV) and the TeV scale. The same brane-world setup to address this hierarchy problem may also in principle address the smallness problem of dark energy. Specifically, the Planck-SM hierarchy ratio was viewed as a quantum gravity-related, dimensionless fine structure constant where various physical energy scales in the system are associated with the Planck mass through different powers of the 'gravity fine structure constant'. In this paper we provide a toy model based on the Randall-Sundrum geometry where SUSY-breaking is induced by the coupling between a SUSY-breaking Higgs field on the brane and the KK gravitinos. We show that the associated Casimir energy density indeed conforms with the dark energy scale.
Date: November 16, 2007
Creator: Chen, Pisin; /SLAC /KIPAC, Menlo Park; Gu, Je-An & /NCTS, Hsinchu
Partner: UNT Libraries Government Documents Department

A Lower Bound on Neutrino Mass And Its Implication on the Z-Burst Scenario

Description: We show that the cascade limit on ultra high energy cosmic neutrino (UHEC/nu) flux imposes a lower bound on the neutrino mass provided that super-GZK events of ultra high energy cosmic rays (UHECRs) are produced from Z-bursts. Based on the data from HiRes and AGASA, the obtained neutrino mass lower bound violates its existing cosmological upper bound. We conclude that the Z-burst cannot be the dominant source for the observed super-GZK UHECR events. This is consistent with the recent ANITA-lite data.
Date: January 11, 2006
Creator: Lai, Kwang-Chang; /Taiwan, Natl. Taiwan U.; Chen, Pisin & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Radiation damping in focusing-dominated systems

Description: A quasi-classical method is developed to calculate the radiation damping of a relativistic particle in a straight, continuous focusing system. In one limiting case where the pitch angle of the particle {theta}{sub p} is much larger than the radiation opening angle 1/{gamma}, the radiation power spectrum is similar to synchrotron radiation and the relative damping rate of the transverse action is proportional to the relative energy loss rate. In the other limiting case where {theta}{sub p} {much_lt} 1/{gamma}, the radiation is dipole in nature and the relative damping rate of the transverse action is energy-independent and is much faster than the relative energy rate. Quantum excitation to the transverse action is absent in this focusing channel. These results can be extended to bent systems provided that the focusing field dominates over the bending field.
Date: June 1, 1995
Creator: Huang, Zhirong; Chen, Pisin & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Radiation and radiation reaction in continuous focusing channels

Description: We show that the radiation damping rate of the transverse action of a particle in a straight, continuous focusing system is independent of the particle energy, and that no quantum excitation is induced. This absolute damping effect leads to the existence of a transverse ground state which the particle inevitably decays to, and yields the minimum beam emittance that one can ever attain, {gamma}{epsilon}{sub min} = {Dirac_h}/2mc, limited only by the uncertainty principle. Due to adiabatic invariance, the particle can be accelerated along the focusing channel in its ground state without any radiation energy loss. These findings may apply to bent systems provided that the focusing field dominates over the bending field.
Date: December 31, 1994
Creator: Huang, Zhirong; Chen, Pisin & Ruth, R. D.
Partner: UNT Libraries Government Documents Department

Analysing the Effect on CMB in a Parity and Charge Parity Violating Varying Alpha Theory

Description: In this paper we study in detail the effect of our recently proposed model of parity and charge-parity (PCP) violating varying alpha on the Cosmic Microwave Background (CMB) photon passing through the intra galaxy-cluster medium (ICM). The ICM is well known to be composed of magnetized plasma. According to our model, the polarization and intensity of the CMB would be affected when traversing through the ICM due to non-trivial scalar photon interactions. We have calculated the evolution of such polarization and intensity collectively, known as the stokes parameters of the CMB photon during its journey through the ICM and tested our results against the Sunyaev-Zel'dovich (SZ) measurement on Coma galaxy cluster. Our model contains a PCP violating parameter, {beta}, and a scale of alpha variation {omega}. Using the derived constrained on the photon-to-scalar conversion probability, {bar P}{sub {gamma}{yields}{phi}}, for Coma cluster in ref.[34] we found a contour plot in the ({omega},{beta}) parameter plane. The {beta} = 0 line in this parameter space corresponds to well-studied Maxwell-dilaton type models which has lower bound on {omega} {approx}> 6.4 x 10{sup 9} GeV. In general, as the absolute value of {beta} increases, lower bound on {omega} also increases. Our model in general predicts the modification of the CMB polarization with a non-trivial dependence on the parity violating coupling parameter {beta}. However, it is unconstrained in this particular study. We show that this effect can in principle be detected in the future measurements on CMB polarization such that {beta} can also be constrained.
Date: September 14, 2012
Creator: Maity, Debaprasad; /NCTS, Taipei /Taiwan, Natl. Taiwan U.; Chen, Pisin & /NCTS, Taipei /Taiwan, Natl. Taiwan U. /KIPAC, Menlo Park /SLAC
Partner: UNT Libraries Government Documents Department

Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe

Description: We propose a phenomenological model for the early universe where there is a smooth transition between an early quintessence phase and a radiation-dominated era. The matter content is modeled by an appropriately modified Chaplygin gas for the early universe. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today. We show that the high frequencies region of the spectrum depends on the free parameter of the model and most importantly this region of the spectrum can be within the reach of future gravitational waves detectors.
Date: June 6, 2012
Creator: Bouhmadi-Lopez, Mariam; /Lisbon, CENTRA; Chen, Pisin; /Taiwan, Natl. Taiwan U. /KIPAC, Menlo Park /SLAC; Liu, Yen-Wei & /Taiwan, Natl. Taiwan U.
Partner: UNT Libraries Government Documents Department