Flavor Field Research Articles

Inference solves a boundary-value collision problem with relevance to neutrino flavor transformation

Understanding neutrino flavor transformation in dense environments such as core-collapse supernovae (CCSN) is critical for inferring the physics of these events and interpreting a detected neutrino signal. The role of direction-changing collisions in shaping the neutrino flavor field in these environments is important and poorly understood; it has not been treated self-consistently. There has been progress, via numerical integration, to include the effects of collisions in the dynamics of the neutrino flavor field. While this has led to important insights, integration is limited by its requirement that full initial conditions must be assumed known. On the contrary, it has been shown in recent years that feedback from collisions to the field is a boundary value problem. Numerical integration techniques are poorly equipped to handle that formulation. This paper demonstrates that an inference formulation of the problem can solve a simple collisions-only model representing a CCSN core--without full knowledge of initial conditions. Specifically, the procedure solves a two-point boundary value problem with partial information at the bounds. The model is sufficiently simple that physical reasoning may be used as a confidence check on the inference-based solution, and the procedure recovers the expected model dynamics. This result demonstrates that inference can solve a problem that is artificially hidden from integration techniques----a problem that is an important feature of flavor evolution in dense environments. Thus, it is worthwhile to explore means of augmenting the existing powerful integration tools with inference-based approaches.

The Effect of Strong Magnetic Field on Heavy Quarkonia in a Hot Medium Using Nikiforov-Uvarov Method

The influence of temperature and a constant strong magnetic field on the quarkonium heavy meson spectrum is explored as a result of recent research suggesting that a strong magnetic field can be formed at primary stage in ultrarelativistic heavy ion collisions (URHIC). Debye screen potential is used in non-relativistic models, and the states are termed as charmonium & bottominum. In order to better understand the current findings, a comparison has been made in recent studies. Therefore, the number of flavor and magnetic field play an essential role in hot medium.

Fast oscillations, collisionless relaxation, and spurious evolution of supernova neutrino flavor

Mounting evidence indicates that neutrinos likely undergo fast flavor conversion (FFC) in at least some core-collapse supernovae. Outcomes of FFC, however, remain highly uncertain. Here we study the cascade of flavor-field power from large angular scales in momentum space down to small ones, showing that FFC enhances this process and thereby hastens relaxation. Cascade also poses a computational challenge, which is present even if the flavor field is stable: When power reaches the smallest angular scale of the calculation, error from truncating the angular-moment expansion propagates back to larger scales, to disastrous effect on the overall evolution. Essentially the same issue has prompted extensive work in the context of plasma kinetics. This link suggests new approaches to averting spurious evolution, a problem that presently puts severe limitations on the feasibility of realistic oscillation calculations.

Spectral swaps in a two-dimensional neutrino ring model

Neutrinos emitted deep within a supernova explosion experience a self-induced index of refraction. In the stationary, one-dimensional (1D) supernova "bulb model", this self-induced refraction can lead to a collective flavor transformation which is coherent among different neutrino momentum modes. Such collective oscillations can produce partial swaps of the energy spectra of different neutrino species as the neutrinos stream away from the proto-neutron star. However, it has been demonstrated that the spatial symmetries (such as the spherical symmetry in the bulb model) can be broken spontaneously by collective neutrino oscillations in multi-dimensional models. Using a stationary, 2D neutrino ring model we demonstrate that there exist two limiting scenarios where collective oscillations may occur. In one limit, the collective flavor transformation begins at a radius with relatively high neutrino densities and develops small-scale flavor structures. The loss of the spatial correlation in the neutrino flavor field results in similar (average) energy spectra for the anti-neutrinos of almost all energies and the neutrinos of relatively high energies. In the other limit, the flavor transformation starts at a radius where the neutrino densities are smaller (e.g., due to the suppression of the high matter density near the proto-neutron star). Although the spatial symmetry is broken initially, it is restored as the neutrino densities decrease, and the neutrinos of different flavors partially swap their energy spectra as in the 1D bulb model. This finding may have interesting ramifications in other aspects of supernova physics.

Holographic entanglement entropy for massive flavours in dS 4

We examine the holographic entanglement entropy of spherical regions in de Sitter space in the presence of massive flavour fields which are modelled by probe D7 branes in AdS_5xS^5. We focus on the finite part of the massive correction to the entropy in the limits of small mass and large mass that are separated by a phase transition between two topologically distinct brane embeddings. For small masses, it approaches the flat space result for small spheres, whereas for large spheres there is a term that goes as the log of the sphere radius. For large masses, we find evidence for a universal contribution logarithmic in the mass. In all cases the entanglement entropy is smooth as the sphere radius crosses the horizon.

Flavour fields in steady state: stress tensor and free energy

The dynamics of a probe brane in a given gravitational background is governed by the Dirac-Born-Infeld action. The corresponding open string metric arises naturally in studying the fluctuations on the probe. In Gauge-String duality, it is known that in the presence of a constant electric field on the worldvolume of the probe, the open string metric acquires an event horizon and therefore the fluctuation modes on the probe experience an effective temperature. In this article, we bring together various properties of such a system to a formal definition and a subsequent narration of the effective thermodynamics and the stress tensor of the corresponding flavour fields, also including a non-vanishing chemical potential. In doing so, we point out a potentially infinitely-degenerate scheme-dependence of regularizing the free energy, which nevertheless yields a universal contribution in certain cases. This universal piece appears as the coefficient of a log-divergence in free energy when a space-filling probe brane is embedded in AdS$_{d+1}$-background, for $d=2, 4$, and is related to conformal anomaly. For the special case of $d=2$, the universal factor has a striking resemblance to the well-known heat current formula in $(1+1)$-dimensional conformal field theory in steady-state, which endows a plausible physical interpretation to it. Interestingly, we observe a vanishing conformal anomaly in $d=6$.

Density fluctuation effects on collective neutrino oscillations in O-Ne-Mg core-collapse supernovae

We investigate the effect of matter density fluctuations on supernova collective neutrino flavor oscillations. In particular, we use full multiangle, three-flavor, self-consistent simulations of the evolution of the neutrino flavor field in the envelope of an O-Ne-Mg core-collapse supernova at shock breakout (neutronization neutrino burst) to study the effect of the matter density ``bump'' left by the He-burning shell. We find a seemingly counterintuitive increase in the overall ${\ensuremath{\nu}}_{\mathrm{e}}$ survival probability created by this matter density feature. We discuss this behavior in terms of the interplay between the matter density profile and neutrino collective effects. While our results give new insights into this interplay, they also suggest an immediate consequence for supernova neutrino burst detection: it will be difficult to use a burst signal to extract information on fossil burning shells or other fluctuations of this scale in the matter density profile. Consistent with previous studies, our results also show that the interplay of neutrino self-coupling and matter fluctuation could cause a significant increase in the ${\ensuremath{\nu}}_{\mathrm{e}}$ survival probability at very low energy.

Weak coupling large-N transitions at finite baryon density

We study thermodynamics of free SU(N) gauge theory with a large number of colours and flavours on a three-sphere, in the presence of a baryon number chemical potential. Reducing the system to a holomorphic large-N matrix integral, paying specific attention to theories with scalar flavours (squarks), we identify novel third-order deconfining phase transitions as a function of the chemical potential. These transitions in the complex large-N saddle point configurations are interpreted as "melting" of baryons into (s)quarks. They are triggered by the exponentially large (~ exp(N)) degeneracy of light baryon-like states, which include ordinary baryons, adjoint-baryons and baryons made from different spherical harmonics of flavour fields on the three-sphere. The phase diagram of theories with scalar flavours terminates at a phase boundary where baryon number diverges, representing the onset of Bose condensation of squarks.

A holographic QCD and excited baryons from string theory

We study baryons of arbitrary isospin in a stringy holographic QCD model. In this D4-D8 holographic setting, the flavor symmetry is promoted to a gauge symmetry in the bulk, and produces, as KK modes of the gauge field, pions and spin one mesons of low energy QCD. Baryons of arbitrary isospins are represented as instanton solitons with isospin and spin quantum numbers locked, in a manner similar to the Skyrmion model. The soliton picture leads to a natural effective field theory of arbitrary baryons interacting with mesons. Couplings of baryons to axial mesons, including pions, are dominated in the large $N_c$ limit by a direct coupling to the flavor field strength in five dimensions. We delineate the relevant couplings and determine their strengths. This work generalizes part of hep-th/0701276 and arXiv:0705.2632 [hep-th] to all excited baryons. Due to technical difficulties in introducing relativistic higher spin fields, we perform all computations in the nonrelativistic regime, which suffices for the leading $N_c$ predictions.