arXiv subjects

Tomislav Prokopec

Publications and source records attributed to Tomislav Prokopec.

At least 109 records · Page 6Linked to original sources

arXiv2008

Two loop stress-energy tensor for inflationary scalar electrodynamics

We calculate the expectation value of the coincident product of two field strength tensors at two loop order in scalar electrodynamics on de Sitter background. The result agrees with the stochastic formulation which we have developed in a companion paper [2] for the nonperturbative resummation of leading logarithms of the scale factor. When combined with a previous computation of scalar bilinears [1], our current result also gives the two loop stress-energy tensor for inflationary scalar electrodynamics. This shows a secular decrease in the vacuum energy which derives from the vacuum polarization induced by the inflationary production of charged scalars.

gr-qc↗

arXiv2007

Decoherence from Isocurvature Perturbations in Inflation

We discuss the possible role of isocurvature perturbations for the quantum decoherence of the curvature perturbation during inflation. We point out that if the inflaton trajectory in field space is curved, the adiabatic mode is generically coupled to the isocurvature mode and thus tracing out the latter can cause the curvature perturbation to decohere. We explicitly investigate this suggestion in a model of inflation with two decoupled massive fields and find that decoherence is effective for a wide range of mass ratios. In particular, we calculate the entanglement entropy for this model and show that it grows after horizon exit, providing a quantitative measure for decoherence.

astro-ph↗

arXiv2007

A graviton propagator for inflation

We construct the scalar and graviton propagator in quasi de Sitter space up to first order in the slow roll parameter $ε\equiv -\dot{H}/H^2$. After a rescaling, the propagators are similar to those in de Sitter space with an $ε$ correction to the effective mass. The limit $ε\to 0$ corresponds to the E(3) vacuum that breaks de Sitter symmetry, but does not break spatial isotropy and homogeneity. The new propagators allow for a self-consistent, dynamical study of quantum back-reaction effects during inflation.

gr-qc↗

arXiv2007

Baryogenesis from the amplification of vacuum fluctuations during inflation

We propose that the baryon asymmetry of the Universe may originate from the amplification of quantum fluctuations of a light complex scalar field during inflation. CP-violation is sourced by complex mass terms, which are smaller than the Hubble rate, as well as non-standard kinetic terms. We find that, when assuming 60 e-folds of inflation, an asymmetry in accordance with observation can result for models where the energy scale of inflation is of the order of 10^16 GeV. Lower scales may be achieved when assuming substantially larger amounts of e-folds.

astro-ph↗

arXiv2007

Quantum radiative corrections to slow-roll inflation

We consider the nonminimally coupled lambda phi^4 scalar field theory in de Sitter space and construct the renormalization group improved renormalized effective theory at the one-loop level. Based on the corresponding quantum Friedmann equation and the scalar field equation of motion, we calculate the quantum radiative corrections to the scalar spectral index n_s, gravitational wave spectral index n_g and the ratio r of tensor to scalar perturbations. When compared with the standard (tree-level) values, we find that the quantum contributions are suppressed by lambda N^2 where N denotes the number of e-foldings. Hence there is an N^2 enhancement with respect to the naive expectation, which is due to the infrared enhancement of scalar vacuum fluctuations characterising de Sitter space. Since observations constrain lambda to be very small lambda ~ 10^(-12) and N ~ 50-60, the quantum corrections in this inflationary model are unobservably small.

astro-ph↗

arXiv2007

Vacuum properties of nonsymmetric gravity in de Sitter space

We consider quantum effects of a massive antisymmetric tensor field on the dynamics of de Sitter space-time. Our starting point is the most general, stable, linearized Lagrangian arising in nonsymmetric gravitational theories (NGTs), where part of the antisymmetric field mass is generated by the cosmological term. We construct a renormalization group (RG) improved effective action by integrating out one loop vacuum fluctuations of the antisymmetric tensor field and show that, in the limit when the RG scale goes to zero, the Hubble parameter -- and thus the effective cosmological constant -- relaxes rapidly to zero. We thus conclude that quantum loop effects in de Sitter space can dramatically change the infrared sector of the on-shell gravity, making the expansion rate insensitive to the original (bare) cosmological constant.

gr-qc↗

arXiv2007

Electroweak Phase Transition and Baryogenesis in the nMSSM

We analyze the nMSSM with CP violation in the singlet sector. We study the static and dynamical properties of the electroweak phase transition. We conclude that electroweak baryogenesis in this model is generic in the sense that if the present limits on the mass spectrum are applied, no severe additional tuning is required to obtain a strong first-order phase transition and to generate a sufficient baryon asymmetry. For this we determine the shape of the nucleating bubbles, including the profiles of CP-violating phases. The baryon asymmetry is calculated using the advanced transport theory to first and second order in gradient expansion presented recently. Still, first and second generation sfermions must be heavy to avoid large electric dipole moments.

hep-ph↗

arXiv2006

Baryogenesis in Brans-Dicke theory

A new mechanism for baryogenesis is proposed in the context of an extended Brans-Dicke (BD) theory. We generalize the BD scalar to complex field with CP violating coupling to curvature and show that the charged BD current can be enhanced during inflationary epoch. After inflation the current decays (via tree level interactions) into the standard model particles. When the BD scalar is charged under baryon and/or lepton number, the decay produces a net baryon number. Rather generically a sufficiently large scalar current can be produced during inflation to account for the observed baryon asymmetry of the Universe. Our baryogensis scenario can in an elegant way be incorporated into a model of extended inflation.

hep-ph↗

arXiv2006

Particle number in kinetic theory

We provide a derivation for the particle number densities on phase space for scalar and fermionic fields in terms of Wigner functions. Our expressions satisfy the desired properties: for bosons the particle number is positive, for fermions it lies in the interval between zero and one, and both are consistent with thermal field theory. As applications we consider the Bunch-Davies vacuum and fermionic preheating after inflation.

hep-th↗

arXiv2006

Problems and hopes in nonsymmetric gravity

We consider the linearized nonsymmetric theory of gravitation (NGT) within the background of an expanding universe and near a Schwarzschild mass. We show that the theory always develops instabilities unless the linearized nonsymmetric lagrangian reduces to a particular simple form. This form contains a gauge invariant kinetic term, a mass term for the antisymmetric metric-field and a coupling with the Ricci curvature scalar. This form cannot be obtained within NGT. Based on the linearized lagrangian we know to be stable, we consider the generation and evolution of quantum fluctuations of the antisymmetric gravitational field (B-field) from inflation up to the present day. We find that a B-field with a mass m ~ 0.03(H_I/10^(13)GeV)^4 eV is an excellent dark matter candidate.

gr-qc↗

arXiv2006

Baryogenesis in the MSSM, nMSSM and NMSSM

We compare electroweak baryogenesis in the MSSM, nMSSM and NMSSM. We comment on the different sources of CP violation, the phase transition and constraints from EDM measurements.

hep-ph↗

arXiv2006

Antisymmetric Metric Field as Dark Matter

We consider the generation and evolution of quantum fluctuations of a massive nonsymmetric gravitational field (B-field) from inflationary epoch to matter era in the simplest variant of the nonsymmetric theory of gravitation (NGT), which consists of a gauge kinetic term and a mass term. We observe that quite generically a nonsymmetric metric field with mass, m_B ~ 0.03(H_I/10^(13) GeV)^4 eV, is a good dark matter candidate, where H_I denotes the inflationary scale. The most prominent feature of this dark matter is a peak in power at a comoving momentum, k ~ sqrt(m_B H_0)/(1+z_eq)^(1/4), where z_eq is the redshift at equality. This scale corresponds roughly to the Earth-Sun distance.

astro-ph↗

arXiv2006

Instabilities in the nonsymmetric theory of gravitation

We consider the linearized nonsymmetric theory of gravitation (NGT) within the background of an expanding universe and near a Schwarzschild metric. We show that the theory always develops instabilities unless the linearized nonsymmetric lagrangian reduces to a particular simple form. This theory contains a gauge invariant kinetic term, a mass term for the antisymmetric metric-field and a coupling with the Ricci curvature scalar. This form cannot be obtained within NGT. Next we discuss NGT beyond linearized level and conjecture that the instabilities are not a relic of the linearization, but are a general feature of the full theory. Finally we show that one cannot add ad-hoc constraints to remove the instabilities as is possible with the instabilities found in NGT by Clayton.

gr-qc↗

arXiv2006

The cosmology of the nonsymmetric theory of gravitation

We show that during cosmological inflation the nonsymmetric metric tensor theory of gravitation develops a spectrum which is potentially observable by cosmic microwave background observations, and may be the most sensitive probe of the scale of cosmic inflation.

astro-ph↗

arXiv2006

A solution to the cosmological constant problem

We argue that, when coupled to Einstein's theory of gravity, the Yukawa theory may solve the cosmological constant problem in the following sense: The radiative corrections of fermions generate an effective potential for the scalar field, such that the effective cosmological term Lambda_eff is dynamically driven to zero. Thence, for any initial positive cosmological constant Lambda_0, Lambda_eff = 0 is an attractor of the semiclassical Einstein theory coupled to fermionic and scalar matter fields. When the initial cosmological term is negative, Lambda_eff=Lambda_0 does not change. Next we argue that the dark energy of the Universe may be explained by a GUT scale fermion with a mass, m = 4.3 * 10^15 (Lambda_0/10^13GeV)^(1/2) GeV. Finally, we comment on how the inflationary paradigm, BEH mechanism and phase transitions in the early Universe get modified in the light of our findings.

gr-qc↗

arXiv2006

Fermion Mass Generation in de Sitter Space

We study the one-loop radiative corrections for massless fermions in de Sitter space induced by a Yukawa coupling to a light, nearly minimally coupled scalar field. We show that the fermions acquire a mass. Next we construct the corresponding (nonlocal) effective fermionic action, which -- in contrast to the case of a massive Dirac fermion -- preserves chirality. Nevertheless, the resulting fermion dynamics is precisely that of a Dirac fermion with a mass proportional to the expansion rate. Our finding supports the view that an observer or a test particle responds to a scalar field in inflation by shifting its energy rather than seeing a thermal bath.

gr-qc↗

arXiv2005

Lamb Shift of Unruh Detector Levels

We argue that the energy levels of an Unruh detector experience an effect similar to the Lamb shift in Quantum Electrodynamics. As a consequence, the spectrum of energy levels in a curved background is different from that in flat space. As examples, we consider a detector in an expanding Universe and in Rindler space, and for the latter case we suggest a new expression for the local virtual energy density seen by an accelerated observer. In the ultraviolet domain, that is when the space between the energy levels is larger than the Hubble rate or the acceleration of the detector, the Lamb shift quantitatively dominates over the thermal response rate.

gr-qc↗

arXiv2005

SO(10)-GUT Coherent Baryogenesis

A model for GUT baryogenesis, coherent baryogenesis within the framework of supersymmetric SO(10), is considered. In particular, we discuss the Barr-Raby model, where at the end of hybrid infl ation charge asymmetries can be created through the time-dependent higgsino-gaugino mixing mass matrix. These asymmetries are processed to Standard Model matter through decays via nonrenormalizable (B-L)-violating operators. We find that a baryon asymmetry in accordance with observation can be generated. An appendix is devoted to provide useful formulas and concrete examples for calculations within SO(10).

hep-ph↗