arXiv subjects

K. Enqvist

Publications and source records attributed to K. Enqvist.

18 recordsLinked to original sources

arXiv2014

The LBNO long-baseline oscillation sensitivities with two conventional neutrino beams at different baselines

The proposed Long Baseline Neutrino Observatory (LBNO) initially consists of $\sim 20$ kton liquid double phase TPC complemented by a magnetised iron calorimeter, to be installed at the Pyhäsalmi mine, at a distance of 2300 km from CERN. The conventional neutrino beam is produced by 400 GeV protons accelerated at the SPS accelerator delivering 700 kW of power. The long baseline provides a unique opportunity to study neutrino flavour oscillations over their 1st and 2nd oscillation maxima exploring the $L/E$ behaviour, and distinguishing effects arising from $δ_{CP}$ and matter. In this paper we show how this comprehensive physics case can be further enhanced and complemented if a neutrino beam produced at the Protvino IHEP accelerator complex, at a distance of 1160 km, and with modest power of 450 kW is aimed towards the same far detectors. We show that the coupling of two independent sub-MW conventional neutrino and antineutrino beams at different baselines from CERN and Protvino will allow to measure CP violation in the leptonic sector at a confidence level of at least $3σ$ for 50\% of the true values of $δ_{CP}$ with a 20 kton detector. With a far detector of 70 kton, the combination allows a $3σ$ sensitivity for 75\% of the true values of $δ_{CP}$ after 10 years of running. Running two independent neutrino beams, each at a power below 1 MW, is more within today's state of the art than the long-term operation of a new single high-energy multi-MW facility, which has several technical challenges and will likely require a learning curve.

hep-ph↗

arXiv2014

Optimised sensitivity to leptonic CP violation from spectral information: the LBNO case at 2300 km baseline

One of the main goals of the Long Baseline Neutrino Observatory (LBNO) is to study the $L/E$ behaviour (spectral information) of the electron neutrino and antineutrino appearance probabilities, in order to determine the unknown CP-violation phase $δ_{CP}$ and discover CP-violation in the leptonic sector. The result is based on the measurement of the appearance probabilities in a broad range of energies, covering t he 1st and 2nd oscillation maxima, at a very long baseline of 2300 km. The sensitivity of the experiment can be maximised by optimising the energy spectra of the neutrino and anti-neutrino fluxes. Such an optimisation requires exploring an extended range of parameters describing in details the geometries and properties of the primary protons, hadron target and focusing elements in the neutrino beam line. In this paper we present a numerical solution that leads to an optimised energy spectra and study its impact on the sensitivity of LBNO to discover leptonic CP violation. In the optimised flux both 1st and 2nd oscillation maxima play an important role in the CP sensitivity. The studies also show that this configuration is less sensitive to systematic errors (e.g. on the total event rates) than an experiment which mainly relies on the neutrino-antineutrino asymmetry at the 1st maximum to determine the existence of CP-violation.

hep-ph↗

arXiv2014

The mass-hierarchy and CP-violation discovery reach of the LBNO long-baseline neutrino experiment

The next generation neutrino observatory proposed by the LBNO collaboration will address fundamental questions in particle and astroparticle physics. The experiment consists of a far detector, in its first stage a 20 kt LAr double phase TPC and a magnetised iron calorimeter, situated at 2300 km from CERN and a near detector based on a high-pressure argon gas TPC. The long baseline provides a unique opportunity to study neutrino flavour oscillations over their 1st and 2nd oscillation maxima exploring the $L/E$ behaviour, and distinguishing effects arising from $δ_{CP}$ and matter. In this paper we have reevaluated the physics potential of this setup for determining the mass hierarchy (MH) and discovering CP-violation (CPV), using a conventional neutrino beam from the CERN SPS with a power of 750 kW. We use conservative assumptions on the knowledge of oscillation parameter priors and systematic uncertainties. The impact of each systematic error and the precision of oscillation prior is shown. We demonstrate that the first stage of LBNO can determine unambiguously the MH to $>5σ$C.L. over the whole phase space. We show that the statistical treatment of the experiment is of very high importance, resulting in the conclusion that LBNO has $\sim$ 100% probability to determine the MH in at most 4-5 years of running. Since the knowledge of MH is indispensable to extract $δ_{CP}$ from the data, the first LBNO phase can convincingly give evidence for CPV on the $3σ$C.L. using today's knowledge on oscillation parameters and realistic assumptions on the systematic uncertainties.

hep-ph↗

arXiv2012

Cosmological inflation

The very basics of cosmological inflation are discussed. We derive the equations of motion for the inflaton field, introduce the slow-roll parameters, and present the computation of the inflationary perturbations and their connection to the temperature fluctuations of the cosmic microwave background.

gr-qc↗

arXiv2008

Parametric Decay of the Curvaton

We argue that the curvaton decay takes place most naturally by way of a broad parametric resonance. The mechanism is analogous to resonant inflaton decay but does not require any tuning of the curvaton coupling strength to other scalar fields. For low scale inflation and a correspondingly low mass scale for the curvaton, we speculate on observable consequences including the possibility of stochastic gravitational waves

astro-ph↗

arXiv2008

On the divergences of inflationary superhorizon perturbations

We discuss the infrared divergences that appear to plague cosmological perturbation theory. We show that within the stochastic framework they are regulated by eternal inflation so that the theory predicts finite fluctuations. Using the $ΔN$ formalism to one loop, we demonstrate that the infrared modes can be absorbed into additive constants and the coefficients of the diagrammatic expansion for the connected parts of two and three-point functions of the curvature perturbation. As a result, the use of any infrared cutoff below the scale of eternal inflation is permitted, provided that the background fields are appropriately redefined. The natural choice for the infrared cutoff would of course be the present horizon; other choices manifest themselves in the running of the correlators. We also demonstrate that it is possible to define observables that are renormalization group invariant. As an example, we derive a non-perturbative, infrared finite and renormalization point independent relation between the two-point correlators of the curvature perturbation for the case of the free single field.

astro-ph↗

arXiv2007

Eternal inflation and localization on the landscape

We model the essential features of eternal inflation on the landscape of a dense discretuum of vacua by the potential $V(ϕ)=V_{0}+δV(ϕ)$, where $|δV(ϕ)|\ll V_{0}$ is random. We find that the diffusion of the distribution function $ρ(ϕ,t)$ of the inflaton expectation value in different Hubble patches may be suppressed due to the effect analogous to the Anderson localization in disordered quantum systems. At $t \to \infty$ only the localized part of the distribution function $ρ(ϕ, t)$ survives which leads to dynamical selection principle on the landscape. The probability to measure any but a small value of the cosmological constant in a given Hubble patch on the landscape is exponentially suppressed at $t\to \infty$.

hep-th↗

arXiv2005

Scalar condensate decay in a fermionic heat bath in the early universe

We consider one-loop thermal effects on the decay of a scalar field zero mode initially dominating the energy density of the universe. We assume fermionic decay channels and take into account the effects due to both particle and hole excitations, and present approximate expressions for the absorption and decay rates. We apply the results to the inflaton and solve the Boltzmann equations to find the temperature evolution of the fermionic plasma. We show that the reheat temperature can be greater than the inflaton mass if the inflaton decays into more than one fermionic species.

hep-ph↗

arXiv2004

Dynamics of MSSM flat directions consisting of multiple scalar fields

Although often chosen because of simplicity, a single scalar field does not provide a general parametrization of an MSSM flat direction. We derive a formalism for a class of gauge invariant polynomials which result in a multifield description of the flat directions. In contrast to the single field case, the vanishing of the gauge currents yields an important dynamical constraint in the multifield framework. We consider in detail the example of the H_uL flat direction and study the dynamical evolution during and after inflation. We highlight the differences between the single and the multifield flat directions. We show that in the multifield case the field space has an intrinsic curvature and hence unsuppressed non-minimal kinetic terms for the flat direction scalars arise. Also the phases of the individual components non-trivially right after inflation, charging the components of the condensate and producing an enhanced entropy after the decay of the condensate, which is due to cross-coupling of different lepton flavours in the F term. However, the qualitative features of the single field Affleck-Dine baryogenesis, such as the produced total charge, remain largely unchanged.

hep-ph↗

arXiv2003

Q-ball dynamics from atomic Bose-Einstein condensates

Relativistic scalar field theories with a conserved global charge Q possess often (meta)stable spherically symmetric soliton solutions, called Q-balls. We elaborate on the perfect formal analogy which exists between Q-balls, and spherically symmetric solitons in certain non-relativistic atomic Bose-Einstein condensates, for which the dominant interatomic interaction can be tuned attractive. In a harmonic trap, present in existing experiments, the Q-ball solution is modified in an essential way. If the trap is significantly prolongated in one direction, however, then genuine solitons do appear, and actual experimental data can be obtained for some of the Q-ball properties studied numerically in the relativistic cosmological context, such as their formation and collisions. We also suggest conditions under which the same cosmologically relevant analogies could be extended to the fully three-dimensional case.

cond-mat.stat-mech↗

arXiv2001

Constraints on self-interacting Q-ball dark matter

We consider different types of Q-balls as self-interacting dark matter. For the Q-balls to act as the dark matter of the universe they should not evaporate, which requires them to carry very large charges; depending on the type, the minimum charge could be as high as Q \sim 10^{33} or the Q-ball coupling to ordinary matter as small as \sim 10^{-35}. The cross-section-to-mass ratio needed for self-interacting dark matter implies a mass scale of m \sim O(1) MeV for the quanta that the Q-balls consist of, which is very difficult to achieve in the MSSM.

hep-ph↗

arXiv2000

Numerical simulations of fragmentation of the Affleck-Dine condensate

We present numerical simulations of fragmentation of the Affleck-Dine condensate in two spatial dimensions. We argue analytically that the final state should consist of both Q-balls and anti-Q-balls in a state of maximum entropy, with most of the balls small and relativistic. Such a behaviour is found in simulations on a 100x100 lattice with cosmologically realistic parameter values. During fragmentation process, we observe filament-like texture in the spatial distribution of charge. The total charge in Q-balls is found to be almost equal to the charge in anti-Q-balls and typically orders of magnitude larger than charge asymmetry. Analytical considerations indicate that, apart from geometrical factors, the results of the simulated two dimensional case should apply also to the fully realistic three dimensional case.

hep-ph↗

arXiv2000

Flat direction condensate instabilities in the MSSM

Coherently oscillating scalar condensates formed along flat directions of the MSSM scalar potential are unstable with respect to spatial perturbations if the potential is flatter than phi^2, resulting in the formation of non-topological solitons such as Q-balls. Using renormalization group we calculate the corrections to the phi^2 potential for a range of flat directions and show that unstable condensates are a generic feature of the MSSM. Exceptions arise for an experimentally testable range of stop and gluino masses when there are large admixtures of stops in the flat direction scalar.

hep-ph↗

arXiv1995

Do subcritical bubbles hinder first order phase transition?

We consider the role played by subcritical bubbles during the electroweak phase transition, estimate their average size, amplitude and formation rate taking into account the crucial role played by thermalization. We also study the influence of subcritical bubbles on the formation of critical bubbles in the thin wall regime and show that, contrary to some recent claims, subcritical bubbles do not affect the nucleation of critical bubbles in an appreciable way. From this fact we conclude that the electroweak baryogenesis scenarios associated with a first order electroweak phase transition still remain an attractive possibility.

hep-ph↗

arXiv1994

Induced Nucleation in Weak First Order Phase Transition

We study induced nucleation by considering the accumulation rate of shrinking subcritical bubbles. We derive the probability for a collection of subcritical bubbles to form a critical bubble, and argue that this mechanism could well play a role in electroweak phase transitions if the Higgs is heavy.

hep-ph↗

arXiv1993

On the Non-Equilibrium Early Universe

We study non--equilibrium ensemble corrections to particle masses and the effective potential in the early universe, using a uniform momentum distribution as an example. The resulting thermalization temperature is computed assuming \sm degrees of freedom, and it is always found to be below $5\times 10^{14}$ GeV, implying that GUT phase transitions typically take place out of equilibrium. For the abelian Higgs model we find that the phase transition is of second order if it occurs before equilibration, in contrast to the first order equilibrium phase transition.

hep-ph↗

arXiv1993

On Primordial Magnetic Fields of Electroweak Origin

We consider Vachaspati's primordial magnetic field which is generated at the electroweak phase transition. Assuming that either the gradients of the Higgs field or, alternatively, the magnetic field itself are stochastic variables with a normal distribution, we find that the resulting magnetic field has an {\em rms} value in the present-day universe which is fully consistent with what is required for the galactic dynamo mechanism.

hep-ph↗

arXiv1992

Cosmological Neutrino Mass Limit Revisited

We consider the equilibration of the 'wrong--helicity' Dirac neutrino states $ν_{+}$ and $\overlineν_{-}$ in the early Universe via weak interactions and calculate carefully the thermally averaged production rate, taking into account all the relevant scattering and decay processes. Requiring that the production rate is less than the Hubble parameter at the onset of QCD phase transition so that the nucleosynthesis predictions are not contradicted, we find for $T_{\rm{QCD}}\simeq 200$ MeV the upper limits $m_{ν_τ}\lsim 740$ keV and $m_{ν_μ}\lsim 480$ keV.

hep-ph↗