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Oscar F. Hernandez

Publications and source records attributed to Oscar F. Hernandez.

18 recordsLinked to original sources
arXiv2014

The Wouthuysen Field Absorption Trough in Cosmic Strings Wakes

The baryon density enhancement in cosmic string wakes leads to a stronger coupling of the spin temperature to the gas kinetic temperate inside these string wakes than in the intergalactic medium (IGM). The Wouthuysen Field (WF) effect has the potential to enhance this coupling to such an extent that it may result in the strongest and cleanest cosmic string signature in the currently planned radio telescope projects. Here we consider this enhancement under the assumption that X-ray heating is not significant. We show that the size of this effect in a cosmic string wake leads to a brightness temperature at least two times more negative than in the surrounding IGM. If the SCI-HI [1, 2] or EDGES [3, 4] experiment confirm a WF absorption trough in the cosmic gas, then cosmic string wakes should appear clearly in 21 cm redshift surveys of z = 10 to 30.

astro-ph.CO↗
arXiv2012

The 21 cm Signature of Shock Heated and Diffuse Cosmic String Wakes

The analysis of the 21 cm signature of cosmic string wakes is extended in several ways. First we consider the constraints on $Gμ$ from the absorption signal of shock heated wakes laid down much later than matter radiation equality. Secondly we analyze the signal of diffuse wake, that is those wakes in which there is a baryon overdensity but which have not shock heated. Finally we compare the size of these signals compared to the expected thermal noise per pixel which dominates over the background cosmic gas brightness temperature and find that the cosmic string signal will exceed the thermal noise of an individual pixel in the Square Kilometre Array for string tensions $Gμ> 2.5 \times 10^{-8}$.

astro-ph.CO↗
arXiv2011

The High-Redshift Neutral Hydrogen Signature of an Anisotropic Matter Power Spectrum

An anisotropic power spectrum will have a clear signature in the 21cm radiation from high-redshift hydrogen. We calculate the expected power spectrum of the intensity fluctuations in neutral hydrogen from before the epoch of reionization, and predict the accuracy to which future experiments could constrain a quadrupole anisotropy in the power spectrum. We find that the Square Kilometer Array will have marginal detection abilities for this signal at z~17 if the process of reionization has not yet started; reionization could enhance the detectability substantially. Pushing to higher redshifts and higher sensitivity will allow highly precise (percent level) measurements of anisotropy.

astro-ph.CO↗
arXiv2005

Polarization States in B -> rho K* and New Physics

The standard-model explanations of the anomalously-large transverse polarization fraction fT in B -> phi K* can be tested by measuring the polarizations of the two decays B+ -> rho+ K*0 and B+ -> rho0 K*+. For the scenario in which the transverse polarizations of both B -> rho K* decays are predicted to be large, we derive a simple relation between the fT's of these decays. If this relation is not confirmed experimentally, this would yield an unambiguous signal for new physics. The new-physics operators which can account for the discrepancy in B -> pi K decays will also contribute to the polarization states of B -> rho K*. We compute these contributions and show that there are only two operators which can simultaneously account for the present B -> pi K and B -> rho K* data. If the new physics obeys an approximate U-spin symmetry, the B -> phi K* measurements can also be explained.

hep-ph↗
arXiv2005

Compton effect: interacting particles or interacting waves

Traditional textbook explanations of the Compton effect treat the photon electron interaction as a particle collision. This explanation is a pedagogical disaster, implying that sometimes interactions are particle-like whereas quantum mechanics always demands that they be wave-like; a photon wavefunction evolves according to a wave equation until its collapse at measurement. If this is so why then does the classical radiation wave equation fail to predict the Compton effect? We address these issues and propose a clearer explanation.

physics.ed-ph↗
arXiv1996

NRQCD matrix elements in polarization of J-Psi produced from b-decay

We present the non-relativistic QCD (NRQCD) prediction for the polarization of the J-Psi produced in b to J-Psi + X, as well as the helicity-summed production rate. We propose that these observables provide a means of measuring the three most important color-octet NRQCD matrix elements involved in J-Psi production. Anticipating the measurement of the polarization parameter alpha, we determine its expected range given current experimental bounds on the color-octet matrix elements.

hep-ph↗
arXiv1995

Particle Production in a Hadron Collider Rapidity Gap: The Higgs Case

Production of rare particles within rapidity gaps has been proposed as a background-free signal for the detection of new physics at hadron colliders. No complete formalism accounts for such processes yet. We study a simple lowest-order QCD model for their description. Concentrating on Higgs production, we show that the calculation of the cross section pp -> pp H can be embedded into existing models which successfully account for diffractive data. We extend those models to take into account single and double diffractive cross sections pp -> H X1 X2 with a gap between the fragments X1 and X2. Using conservative scenarios, we evaluate the uncertainties in our calculation, and study the dependence of the cross section on the gap width. We predict that Higgs production within a gap of 4 units of rapidity is about 0.3 pb for a 100 GeV Higgs at the Tevatron, and almost 2 pb for a 400 GeV Higgs within a gap of 6 units at the LHC with 14 TeV beams.

hep-ph↗
arXiv1995

Broken SU(3) Symmetry in Two-Body B Decays

The decays of $B$ mesons to two-body hadronic final states are analyzed within the context of broken flavor SU(3) symmetry, extending a previous analysis involving pairs of light pseudoscalars to decays involving one or two charmed quarks in the final state. A systematic program is described for learning information {}from decay rates regarding (i) SU(3)-violating contributions, (ii) the magnitude of exchange and annihilation diagrams (effects involving the spectator quark), and (iii) strong final-state interactions. The implication of SU(3)-breaking effects for the extraction of weak phases is also examined. The present status of data on these questions is reviewed and suggestions for further experimental study are made.

hep-ph↗
arXiv1995

ELECTROWEAK PENGUINS AND TWO-BODY B DECAYS

We discuss the role of electroweak penguins in $B$ decays to two light pseudoscalar mesons. We confirm that the extraction of the weak phase $α$ through the isospin analysis involving $B\toππ$ decays is largely unaffected by such operators. However, the methods proposed to obtain weak and strong phases by relating $B\toππ$, $B\toπK$ and $B\to KK$ decays through flavor SU(3) will be invalidated if electroweak penguins are large. We show that, although the introduction of electroweak penguin contributions introduces no new amplitudes of flavor SU(3), there are a number of ways to experimentally measure the size of such effects. Finally, using SU(3) amplitude relations we present a new way of measuring the weak angle $γ$ which holds even in the presence of electroweak penguins.

hep-ph↗
arXiv1995

How To Use SU(3)-Flavor Symmetry to Extract CP Violating Phases and Strong Phase Shifts at CLEO

After a short introduction to the SM picture of CP violation, we discuss recent work on how to use SU(3) flavor symmetry, along with some dynamical approximations, to extract the CKM weak phases and the strong rescattering phases from experimental measurements alone. This suprising wealth of information depends on our two strongest assumptions: SU(3) invariance, and the relative unimportance of exhange and annihilation diagrams. We discuss soon to be measured decay rate measurements that will test the validity of these assumptions.

hep-ph↗
arXiv1994

Triangles, Triangles, Triangles: CP Violation in the B System and the Measurement of Strong and Weak Phases

We present the current wisdom regarding the measurement of the CP-violating phases of the CKM unitarity triangle in $B$-meson decays. After an introduction to the SM picture of CP violation, we review direct and indirect CP violation, the role of penguins and isospin analysis, and $B\to DK$ decays. We also discuss recent work on how to use SU(3) flavor symmetry, along with some dynamical approximations, to get at the CKM weak phases. Through time-independent $B$-decay measurements alone, we show that it is possible to extract all information: the weak phases, the incalculable strong phase shifts, and the sizes of the tree, color-suppressed, and penguin contributions to these decays.

hep-ph↗
arXiv1994

Tadpole-Improved Perturbation Theory for Heavy-Light Lattice Operators

Lattice calculations of matrix elements involving heavy-light quark bilinears are of interest in calculating a variety of properties of B and D mesons, including decay constants and mixing parameters. A large source of uncertainty in the determination of these properties has been uncertainty in the normalization of the lattice-regularized operators that appear in the matrix elements. Tadpole-improved perturbation theory, as formulated by Lepage and Mackenzie, promises to reduce these uncertainties below the ten per cent level at one-loop. In this paper we study this proposal as it applies to lattice-regularized heavy-light operators. We consider both the commonly used zero-distance bilinear and the distance-one point-split operator. A self-contained section on the application of these results is included. The calculation reduces the value of $f_B$ obtained from lattice calculations using the heavy quark effective theory.

hep-lat↗
arXiv1994

Measuring Strong and Weak Phases in Time-Independent B Decays

Flavor SU(3) symmetry implies certain relations among $B$-decay amplitudes to $ππ$, $πK$ and $K {\bar K}$ final states, when annihilation-like diagrams are neglected. Using three triangle relations, we show how to measure the weak CKM phases $α$ and $γ$ using time-independent rate measurements only. In addition, one obtains all the strong final-state phases and the magnitudes of individual terms describing tree (spectator), color-suppressed and penguin diagrams. Many independent measurements of these quantities can be made with this method, which helps to eliminate possible discrete ambiguities and to estimate the size of SU(3)-breaking effects.

hep-ph↗
arXiv1994

Decays of $B$ Mesons to Two Light Pseudoscalars

The decays $B \to PP$, where $P$ denotes a pseudoscalar meson, are analyzed, with emphasis on charmless final states. Numerous triangle relations for amplitudes hold within SU(3) symmetry, relating (for example) the decays $B^+ \to π^+ π^0,~ π^0 K^+$, and $π^+ K^0$. Such relations can improve the possibilities for early detection of $CP$-violating asymmetries. Within the context of a graphical analysis of decays, relations are analyzed among SU(3) amplitudes which hold if some graphs are neglected. One application is that measurements of the rates for the above three $B^+$ decays and their charge-conjugates can be used to determine a weak CKM phase. With measurements of the remaining rates for $B$ decays to $ππ,~πK$, and $K \bar K$, one can obtain two CKM phases and several differences of strong phase shifts.

hep-ph↗
arXiv1992

Point-Split Lattice Operators for B Decays

The matrix element which determines the B meson decay constant can be measured on the lattice using an effective field theory for heavy quarks. Various discretizations of the heavy-light bilinears which appear in this and other B decay matrix elements are possible. The heavy-light bilinear currently used for the determination of the B meson decay constant on the lattice suffers a substantial one-loop renormalization. In this paper, we compute the one-loop renormalizations of the discretizations in which the heavy and light fields in the bilinear are separated by one lattice spacing, and discuss their application. Readers of this paper may also be interested in our paper on the application of Symanzik's improvement program to heavy-light currents (paper number 9203221 on hep-ph).

hep-lat↗
arXiv1992

Improved Heavy Quark Effective Theory Currents

It is hoped that the accuracy of a variety of lattice calculations will be improved by perturbatively eliminating effects proportional to the lattice spacing. In this paper, we apply this improvement program to the heavy quark effective theory currents which cause a heavy quark to decay to a light quark, and renormalize the resulting operators to order $\alphaS$. We find a small decrease in the amount that the operator needs to be renormalized, relative to the unimproved case.

hep-ph↗
arXiv1992

Extended Color Models with a Heavy Top Quark

We present a class of models in which the top quark, by mixing with new physics at a higher energy scale, is naturally heavier than the other standard model particles. We take this new physics to be extended color. Our models contain new particles with masses between 100 GeV and 1 TeV, some of which may be just within the reach of the next generation of experiments. In particular one of our models implies the existence of two right handed top quarks. These models demonstrate the existence of a standard model-like theory consistent with experiment, and leading to new physics below the TeV scale, in which the third generation is treated differently than the first two.

hep-ph↗