arXiv subjects

R. Rosenfeld

Publications and source records attributed to R. Rosenfeld.

At least 73 records · Page 4Linked to original sources

arXiv2008

Physical approximations for the nonlinear evolution of perturbations in dark energy scenarios

The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy as well, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model, and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.

astro-ph↗

arXiv2008

New Physics at the LHC: A Les Houches Report. Physics at Tev Colliders 2007 -- New Physics Working Group

We present a collection of signatures for physics beyond the standard model that need to be explored at the LHC. The signatures are organized according to the experimental objects that appear in the final state, and in particular the number of high pT leptons. Our report, which includes brief experimental and theoretical reviews as well as original results, summarizes the activities of the "New Physics'' working group for the "Physics at TeV Colliders" workshop (Les Houches, France, 11-29 June, 2007).

hep-ph↗

arXiv2008

First-order formalism for dark energy and dust

This work deals with first-order formalism for dark energy and dust in standard cosmology, for models described by real scalar field in the presence of dust in spatially flat space. The field dynamics may be standard or tachyonic, and we show how the equations of motion can be solved by first-order differential equations. We investigate a model to illustrate how the dustlike matter may affect the cosmic evolution using this framework.

astro-ph↗

arXiv2008

Dynamical Mutation of Dark Energy

We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.

astro-ph↗

arXiv2007

Structure formation in the presence of dark energy perturbations

We study non-linear structure formation in the presence of dark energy. The influence of dark energy on the growth of large-scale cosmological structures is exerted both through its background effect on the expansion rate, and through its perturbations as well. In order to compute the rate of formation of massive objects we employ the Spherical Collapse formalism, which we generalize to include fluids with pressure. We show that the resulting non-linear evolution equations are identical to the ones obtained in the Pseudo-Newtonian approach to cosmological perturbations, in the regime where an equation of state serves to describe both the background pressure relative to density, and the pressure perturbations relative to the density perturbations as well. We then consider a wide range of constant and time-dependent equations of state (including phantom models) parametrized in a standard way, and study their impact on the non-linear growth of structure. The main effect is the formation of dark energy structure associated with the dark matter halo: non-phantom equations of state induce the formation of a dark energy halo, damping the growth of structures; phantom models, on the other hand, generate dark energy voids, enhancing structure growth. Finally, we employ the Press-Schechter formalism to compute how dark energy affects the number of massive objects as a function of redshift.

astro-ph↗

arXiv2007

The Higgs portal and an unified model for dark energy and dark matter

We examine a scenario where the Higgs boson is coupled to an additional singlet scalar field which we identify with a quintessence field. We show that this results in an unified picture of dark matter and dark energy, where dark energy is the zero-mode classical field rolling the usual quintessence potential and the dark matter candidate is the quantum excitation (particle) of the field, which is produced in the universe due to its coupling to the Higgs boson.

hep-ph↗

arXiv2007

Microscopic Origin of Non-Gaussian Distributions of Financial Returns

In this paper we study the possible microscopic origin of heavy-tailed probability density distributions for the price variation of financial instruments. We extend the standard log-normal process to include another random component in the so-called stochastic volatility models. We study these models under an assumption, akin to the Born-Oppenheimer approximation, in which the volatility has already relaxed to its equilibrium distribution and acts as a background to the evolution of the price process. In this approximation, we show that all models of stochastic volatility should exhibit a scaling relation in the time lag of zero-drift modified log-returns. We verify that the Dow-Jones Industrial Average index indeed follows this scaling. We then focus on two popular stochastic volatility models, the Heston and Hull-White models. In particular, we show that in the Hull-White model the resulting probability distribution of log-returns in this approximation corresponds to the Tsallis (t-Student) distribution. The Tsallis parameters are given in terms of the microscopic stochastic volatility model. Finally, we show that the log-returns for 30 years Dow Jones index data is well fitted by a Tsallis distribution, obtaining the relevant parameters.

q-fin.ST↗

arXiv2007

Technicolor contribution to lepton + photon + missing energy events at the Tevatron

Events with one lepton, one photon and missing energy are the subject of recent searches at the Fermilab Tevatron. We compute possible contributions to these type of events from the process p pbar --> photon l nu_l nu_tau nubar_tau, where l=e,mu in the context of a Low Scale Technicolor Model. We find that with somewhat tighter cuts than the ones used in the CDF search, it could be possible to either confirm or exclude this model in a small region of its parameter space.

hep-ph↗

arXiv2007

Consequences of dark matter-dark energy interaction on cosmological parameters derived from SNIa data

Models where the dark matter component of the universe interacts with the dark energy field have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. In these models the mass of the cold dark matter particles is a function of the dark energy field responsible for the present acceleration of the universe, and different scenarios can be parameterized by how the mass of the cold dark matter particles evolves with time. In this article we study the impact of a constant coupling $δ$ between dark energy and dark matter on the determination of a redshift dependent dark energy equation of state $w_{DE}(z)$ and on the dark matter density today from SNIa data. We derive an analytical expression for the luminosity distance in this case. In particular, we show that the presence of such a coupling increases the tension between the cosmic microwave background data from the analysis of the shift parameter in models with constant $w_{DE}$ and SNIa data for realistic values of the present dark matter density fraction. Thus, an independent measurement of the present dark matter density can place constraints on models with interacting dark energy.

astro-ph↗

arXiv2005

Relic abundance of mass-varying cold dark matter particles

In models of coupled dark energy and dark matter the mass of the dark matter particle depends on the cosmological evolution of the dark energy field. In this note we exemplify in a simple model the effects of this mass variation on the relic abundance of cold dark matter.

astro-ph↗

arXiv2005

A Simple Model for Quintessential Inflation

We describe a simple toy model for quintessential inflation where a complex scalar field described by a lagrangian with a Peccei-Quinn U(1) symmetry spontaneously broken at a high energy scale and explicitly broken by instanton effects at a much lower energy can account for both the early inflationary phase and the recent accelerated expansion of the Universe. The real part of the complex field plays the role of the inflaton whereas the imaginary part, the "axion", is the quintessence field.

astro-ph↗

arXiv2004

Constraints on a scalar-pseudoscalar Higgs mixing at future e+e- colliders: an update

We perform an update of our previous analysis on the constraints on possible deviations of Hbb coupling from its Standard Model value, arising from a scalar-pseudoscalar mixing. In this paper we include a complete simulation of the process e+ e- -> b bbar e+ e- and combine it with our previous results to obtain tighter bounds on the deviations of the parameters describing this coupling that could be measured at the Next Linear Collider.

hep-ph↗

arXiv2004

Instant preheating mechanism and UHECR

Top-down models assume that the still unexplained Ultra High Energy Cosmic Rays (UHECR's) are the decay products of superheavy particles. Such particles may have been produced by one of the post-inflationary reheating mechanisms and may account for a fraction of the cold dark matter. In this paper, we assess the phenomenological applicability of the simplest instant preheating framework not to describe a reheating process, but as a mechanism to generate relic supermassive particles as possible sources of UHECR's. We use cosmic ray flux and cold dark matter observational data to constrain the parameters of the model.

astro-ph↗

arXiv2003

Higgs production and decay in the little Higgs model

We analyse the consequences of the little Higgs model for double Higgs boson production at the LHC and for the partial decay width of the Higgs into two photons. In particular, we study the sensitivity of these processes in terms of the parameters of the model. We find that the little Higgs model contributions are proportional to (v/f)^4 and hence do not change significantly either single or double Higgs production at hadron colliders or the partial decay width of the Higgs into two photons as compared to the standard model predictions. However, when interference and mixing effects are properly taken into account these contributions increase to be of the order of (v/f)^2.

hep-ph↗

arXiv2002

Preheating in Quintessential Inflation

We perform a numerical study of the preheating mechanism of particle production in models of quintessential inflation and compare it with the usual gravitational production mechanism. We find that even for a very small coupling between the inflaton field and a massless scalar field, g > 10^{-9}, preheating dominates over gravitational particle production. Reheating temperatures in the range 10^{-2} GeV < T_{rh} < 10^{15} GeV can be easily obtained.

hep-ph↗

arXiv2002

Future e^+ e^- Colliders Sensitivity to H b b-bar Coupling and CP Violation

We perform a complete simulation of the process e^+ e^- --> b b-bar nu nu-bar, where nu can be an electron, muon or tau neutrino, in the context of a general Higgs coupling to b quarks. We parametrize the H b b-bar coupling as m_b/v (a + i gamma_5 b). Taking into account interference effects between pure Higgs and Standard Model contributions, we find that sensitivities of the order of 2% and 20% can be obtained at a future e^+ e^- collider for deviations of the $a$ and $b$ parameters respectively from their Standard Model values. Combining our analysis with an independent measurement of Gamma_{H --> b b-bar} can provide evidence about the CP nature of the Higgs sector.

hep-ph↗

arXiv2002

Triple Photon Production at the Tevatron in Technicolor Models

We study the process p bar{p} --> gamma gamma gamma as a signal for associated photon-technipion production at the Tevatron. This is a clean signature with relatively low background. Resonant and non-resonant contributions are included and we show that technicolor models can be effectively probed in this mode.

hep-ph↗

arXiv2002

Measuring Higgs Coupling to Tau-Leptons at Future e+ e- Colliders

We perform a complete simulation of the process $ e^+ e^- \to τ^+ τ^- ν\barν$, where $ν$ can be an electron, muon or tau neutrino, in the context of a general Higgs coupling to $τ$ leptons. We analyse various kinematical distributions and obtain the sensitivity regions in the parameter space that can be explored at a future $e^+ e^-$ collider. In particular, inclusion of $W$ boson fusion enhances the sensitivity significantly.

hep-ph↗