Scholarly Articles, Institute for Particle, Nuclear and Astronomical Sciences (IPNAS)

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Background independent quantum mechanics and gravity
Minic, Djordje; Tze, C. H. (American Physical Society, 2003-09-15)
We argue that the demand of background independence in a quantum theory of gravity calls for an extension of standard geometric quantum mechanics. We discuss a possible kinematical and dynamical generalization of the latter by way of a quantum covariance of the state space. Specifically, we apply our scheme to the problem of a background independent formulation of matrix theory.
Charge assignments in multiple-U(1) gauge theories
Loinaz, William; Takeuchi, Tatsu (American Physical Society, 1999-12-01)
We discuss the choice of gauge field basis in multiple-U(1) gauge theories. We find that there is a preferred basis, specified by the charge orthogonality condition, in which the U(1) gauge fields do not mix under one-loop renormalization group running. [S0556-2821(99)04219-8].
Charge assignments in multiple-U(1) gauge theories
Loinaz, William; Takeuchi, Tatsu (American Physical Society, 1999-12-01)
Constraints on R-parity violating couplings from CERN LEP and SLAG SLD hadronic observables
Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-07-01)
We analyze the one loop corrections to hadronic Z decays in an R-parity violating extension to the minimal supersymmetric standard model. Performing a global fit to all the hadronic observables at the Z peak, we obtain stringent constraints on the R-violating coupling constants lambda' and lambda". The presence of these couplings worsens the agreement with the data relative to the standard model. The strongest constraints come from the b asymmetry parameters A(b) and A(FB)(b) From a classical statistical analysis we find that the couplings lambda'(131), lambda'(132), and lambda"(321) are ruled out at the 1 sigma level, and that lambda'(133) and lambda"(33i) are ruled out at the 2 sigma level. A Bayesian statistical analysis weakens the bounds, but the corresponding chi(2)'s are uncomfortably large, rendering the relevance of the Bayesian bounds suspect.
Constraints on R-parity violating couplings from lepton universality
Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-07-01)
We analyze the one loop corrections to leptonic W and Z decays in an R-parity violating extension to the minimal supersymmetric standard model. We find that lepton universality violation in the Z line-shape variables alone would strengthen the bounds on the magnitudes of the lambda' couplings, but a global fit on all data leaves the bounds virtually unchanged at \lambda'(33k)\less than or equal to 0.42 and \lambda'(23k)\less than or equal to 0.50 at the 2 sigma level. Bounds from W decays are less stringent: \lambda'(33k)\less than or equal to 2.4 at 2 sigma, as a consequence of the weaker Fermilab experimental bounds on lepton universality violation in W decays. We also point out the potential of constraining R-parity violating couplings from the measurement of the Y invisible width.
Constraints on two-Higgs-doublet models at large tan beta from W and Z decays
Lebedev, O.; Loinaz, William; Takeuchi, Tatsu (American Physical Society, 2000-09-01)
We study constraints on type-II two-Higgs-doublet models at large tan beta from CERN LEP and SLD Z-pole data and from lepton universality violation in W decay. We perform a global fit and find that, in the context of Z decay, the LEP-SLD experimental values for lepton universality violation, R-b, and A(b) all somewhat disfavor the model. Contributions from the neutral-Higgs sector can be used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions from the charged-Higgs sector allow us to constrain the charged-Higgs boson mass. For tan beta=100 we obtain the 1 sigma classical (Bayesian) bounds of m(H+/-) greater than or equal to 670 GeV (370 GeV) and 1 greater than or equal to m(h)0/m(A)0/(alpha = beta) =m(H)0/m(A)0/(alpha=0) greater than or equal to 0.68 (0.64). The 2 sigma bounds are weak. Currently, the Fermilab Tevatron experimental limits on lepton universality violation in W decay provide no significant constraint on the Higgs sector.
Effect of the minimal length uncertainty relation on the density of states and the cosmological constant problem
Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)
We investigate the effect of the minimal length uncertainty relation, motivated by perturbative string theory, on the density of states in momentum space. The relation is implemented through the modified commutation relation [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta(')(p) over cap (i)(p) over cap (j)]. We point out that this relation, which is an example of a UV/IR relation, implies the finiteness of the cosmological constant. While our result does not solve the cosmological constant problem, it does shed new light on the relation between this outstanding problem and UV/IR correspondence. We also point out that the blackbody radiation spectrum will be modified at higher frequencies, but the effect is too small to be observed in the cosmic microwave background spectrum.
Exact solution of the harmonic oscillator in arbitrary dimensions with minimal length uncertainty relations
Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Takeuchi, Tatsu (American Physical Society, 2002-06-15)
We determine the energy eigenvalues and eigenfunctions of the harmonic oscillator where the coordinates and momenta are assumed to obey the modified commutation relations [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta(')(p) over cap (i)(p) over cap (j)]. These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relations which appear in perturbative string theory. Our solutions illustrate how certain features of string theory may manifest themselves in simple quantum mechanical systems through the modification of the canonical commutation relations. We discuss whether such effects are observable in precision measurements on electrons trapped in strong magnetic fields.
Glueball spectrum of pure Yang-Mills theory in 2+1 dimensions
Leigh, R. G.; Minic, Djordje; Yelnikov, A. (American Physical Society, 2007-09)
We present details of the analytic computation of the spectrum of lowest spin glueballs in pure Yang-Mills theory in 2+1 dimensions. The new ingredient is provided by the conjectured new nontrivial expression for the (quasi)Gaussian part of the ground state wave functional. We show that this wave functional can be derived by solving the Schrodinger equation under certain assumptions. The mass spectrum of the theory is determined by the zeros of Bessel functions, and the agreement with available lattice data is excellent.
Leptonic CP violation search and the ambiguity of delta m(31)(2)
Koike, M.; Okamura, Naotoshi; Saito, M.; Takeuchi, Tatsu (American Physical Society, 2006-03)
We consider a search for the CP-violating angle delta(CP) in long baseline neutrino oscillation experiments. We show that the subleading delta(CP)-dependent terms in the nu(mu)->nu(e) oscillation probability can be easily obscured by the ambiguity of the leading term which depends on parallel to delta m(31)(2)parallel to. It is thus necessary to determine the value of delta m(31)(2) with a sufficient accuracy. The nu(mu) survival events, which can be accumulated simultaneously with the nu(e) appearance events, can serve for this purpose owing to its large statistics. Therefore, the combined analysis of nu(e) appearance and nu(mu) survival events is crucial to provide a restrictive constraint on delta(CP). Taking a test experimental setup, we demonstrate in the delta(CP)-delta m(31)(2) plane that the analysis of nu(e) appearance events leads to less restrictive constraints on the value of delta(CP) due to the ambiguity of delta m(31)(2) and that the combined analysis efficiently improves the constraints.
Mass, entropy, and holography in asymptotically de Sitter spaces
Balasubramanian, V.; de Boer, J.; Minic, Djordje (American Physical Society, 2002-06-15)
We propose a novel prescription for computing the boundary stress tensor and charges of asymptotically de Sitter (dS) spacetimes from data at early or late time infinity. If there is a holographic dual to dS spaces, defined analogously to the AdS/conformal field theory correspondence, our methods compute the (Euclidean) stress tensor of the dual. We compute the masses of Schwarzschild-de Sitter black holes in four and five dimensions, and the masses and angular momenta of Kerr-de Sitter spaces in three dimensions. All these spaces are less massive than de Sitter space, a fact which we use to qualitatively and quantitatively relate de Sitter entropy to the degeneracy of possible dual field theories. Our results in general dimensions lead to a conjecture: Any asymptotically de Sitter spacetime with mass greater than de Sitter space has a cosmological singularity. Finally, if a dual to de Sitter space exists, the trace of our stress tensor computes the renormalized group (RG) equation of the dual field theory. Cosmological time evolution corresponds to RG evolution in the dual. The RG evolution of the c function is then related to changes in accessible degrees of freedom in an expanding universe.
Monte Carlo simulation calculation of the critical coupling constant for two-dimensional continuum phi(4) theory
Loinaz, William; Willey, R. S. (American Physical Society, 1998-10)
We perform a Monte Carlo simulation calculation of the critical coupling constant for the continuum two-dimensional (lambda/4) phi(4) theory. The critical coupling constant we obtain is [lambda/mu(2)](crit) = 10.26(-.04)(+.08). [S0556-2821(98)07219-1].
Notes on spacetime thermodynamics and the observer dependence of entropy
Marolf, D.; Minic, Djordje; Ross, S. F. (American Physical Society, 2004-03)
Because of the Unruh effect, accelerated and inertial observers differ in their description of a given quantum state. The implications of this effect are explored for the entropy assigned by such observers to localized objects that may cross the associated Rindler horizon. It is shown that the assigned entropies differ radically in the limit where the number of internal states n becomes large. In particular, the entropy assigned by the accelerated observer is a bounded function of n. General arguments are given along with explicit calculations for free fields. The implications for discussions of the generalized second law and proposed entropy bounds are also discussed.
NuTeV anomaly, lepton universality, and nonuniversal neutrino-gauge couplings
Loinaz, William; Okamura, Naotoshi; Rayyan, S.; Takeuchi, Tatsu; Wijewardhana, L. C. R. (American Physical Society, 2004-12)
In previous studies we found that models with flavor-universal suppression of the neutrino-gauge couplings are compatible with NuTeV and Z-pole data. In this paper we expand our analysis to obtain constraints on flavor-dependent coupling suppression by including lepton universality data from W, tau, pi and K decays in fits to model parameters. We find that the data are consistent with a variety of patterns of coupling suppression. In particular, in scenarios in which the suppression arises from the mixing of light neutrinos with heavy gauge singlet states (neutrissimos), we find patterns of flavor-dependent coupling suppression which are also consistent with constraints from mu-->egamma.
NuTeV anomaly, neutrino mixing, and a heavy Higgs boson
Loinaz, William; Okamura, Naotoshi; Takeuchi, Tatsu; Wijewardhana, L. C. R. (American Physical Society, 2003-04)
Recent results from the NuTeV experiment at Fermilab and the deviation of the Z invisible width, measured at CERN LEP and the SLAC Linear Collider, from its standard model (SM) prediction suggest the suppression of neutrino-Z couplings. Such suppressions occur naturally in models which mix the neutrinos with heavy gauge singlet states. We postulate a universal suppression of the Znunu couplings by a factor of (1-epsilon) and perform a fit to the Z-pole and NuTeV observables with epsilon and the oblique correction parameters S and T. Compared to a fit with S and T only, the inclusion of epsilon leads to a dramatic improvement in the quality of the fit. The values of S and T preferred by the fit can be obtained within the SM by a simple increase in the Higgs boson mass. However, if the W mass is also included in the fit, a non-zero U parameter becomes necessary which cannot be supplied within the SM. The preferred value of epsilon suggests that the seesaw mechanism may not be the reason why neutrinos are so light.
Quantum gravity, torsion, parity violation, and all that
Freidel, L.; Minic, Djordje; Takeuchi, Tatsu (American Physical Society, 2005-11)
We discuss the issue of parity violation in quantum gravity. In particular, we study the coupling of fermionic degrees of freedom in the presence of torsion and the physical meaning of the Immirzi parameter from the viewpoint of effective field theory. We derive the low-energy effective Lagrangian which turns out to involve two parameters: one measuring the nonminimal coupling of fermions in the presence of torsion, the other being the Immirzi parameter. In the case of nonminimal coupling the effective Lagrangian contains an axial-vector interaction leading to parity violation. Alternatively, in the case of minimal coupling there is no parity violation and the effective Lagrangian contains only the usual axial-axial interaction. In this situation the real values of the Immirzi parameter are not at all constrained. On the other hand, purely imaginary values of the Immirzi parameter lead to violations of unitarity for the case of nonminimal coupling. Finally, the effective Lagrangian blows up for the positive and negative unit imaginary values of the Immirzi parameter.
Quark-lepton unification and lepton flavor nonconservation from a TeV-scale seesaw neutrino mass texture
Loinaz, William; Okamura, Naotoshi; Rayyan, S.; Takeuchi, Tatsu; Wijewardhana, L. C. R. (American Physical Society, 2003-10-01)
In a recent paper we pointed out that the mixing of the light neutrinos with heavy gauge singlet states could reconcile the Z-pole data from e(+)e(-) colliders and the nu(mu) ((nu) over bar (mu)) scattering data from the NuTeV experiment at Fermilab. We further noted that the mixing angle required to fit the data is much larger than what would be expected from the conventional seesaw mechanism. In this paper, we show how such mixings can be arranged by a judicious choice of the neutrino mass texture. We also argue that by invoking the unification of the Dirac mass matrix for the up-type quarks and the neutrinos, the mass of the heavy states can naturally be expected to lie in the few TeV range. The model is strongly constrained by the lepton flavor changing process mu-->egamma which requires lepton universality to be violated in the charged channel.
Relating the cosmological constant and supersymmetry breaking in warped compactifications of IIB string theory
Berglund, Per; Hubsch, T.; Minic, Djordje (American Physical Society, 2003-02-15)
It has been suggested that the observed value of the cosmological constant is related to the supersymmetry breaking scale M-susy through the formula Lambdasimilar toM(p)(4)(M-susy/M-p)(8). We point out that a similar relation naturally arises in the codimension two solutions of warped spacetime varying compactifications of string theory, in which nonisotropic stringy moduli induce a small but positive cosmological constant.
Short distance versus long distance physics: The classical limit of the minimal length uncertainty relation
Benczik, S. Z.; Chang, Lay Nam; Minic, Djordje; Okamura, Naotoshi; Rayyan, S.; Takeuchi, Tatsu (American Physical Society, 2002-07-15)
We continue our investigation of the phenomenological implications of the "deformed" commutation relations [(x) over cap (i),(p) over cap (j)]=i (h) over bar[(1+beta(p) over cap (2))delta(ij)+beta'(p) over cap (i)(p) over cap (j)]. These commutation relations are motivated by the fact that they lead to the minimal length uncertainty relation which appears in perturbative string theory. In this paper, we consider the effects of the deformation on the classical orbits of particles in a central force potential. Comparison with observation places severe constraints on the value of the minimum length.
Thermal production of axions in the Earth
Davoudiasl, H.; Huber, Patrick (American Physical Society, 2009-05)
We estimate the production rate of axion-type particles in the core of the Earth, at a temperature T approximate to 5000 K. We constrain thermal geo-axion emission by demanding a core-cooling rate less than O(100) K/Gyr, as suggested by geophysics. This yields a "nonstellar" (unaffected by extreme stellar temperatures or densities) bound on the axion-electron (ae) fine structure constant, alpha(ae)less than or similar to 10(-18), stronger than the existing accelerator (vacuum) bound by 4 orders of magnitude. We consider the prospects for measuring the geo-axion flux through conversion into photons in a geoscope; such measurements can further constrain alpha(ae).

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