| 1. |
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| 2. |
- Abele, H., et al.
(författare)
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Particle physics at the European Spallation Source
- 2023
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Ingår i: Physics reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 1023, s. 1-84
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Forskningsöversikt (refereegranskat)abstract
- Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will be the world’s brightest neutron source. As such, it has the potential for a particle physics program with a unique reach and which is complementary to that available at other facilities. This paper describes proposed particle physics activities for the ESS. These encompass the exploitation of both the neutrons and neutrinos produced at the ESS for high precision (sensitivity) measurements (searches).
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| 3. |
- Beiming, Christoffer, et al.
(författare)
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Phenomenological mass model for exotic hadrons and predictions for masses of non-strange dibaryons as hexaquarks
- 2022
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Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213 .- 1873-1562. ; 974, s. 115616-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mass spectra of exotic hadrons known as hexaquarks in the form of dibaryons. We use a phenomenological model based on an extended version of the Giirsey-Radicati mass formula for hadrons to include non-charmed baryons, charmed baryons, and non-strange dibaryons to be able to predict masses of potential dibaryon states. We perform six numerical fits of this model to input data for three different sets of masses of baryons and dibaryons. We find that the model can fit some of the data sets well, especially the sets including charmed baryons and non-strange dibaryons, and observe that the predicted mass of one of the dibaryons is close to the measured mass of the observed hexaquark candidate d * (2380) reported by the WASA-at-COSY experiment. The predicted mass of the deuteron is slightly larger than its measured mass. Finally, for the data sets including charmed baryon and non-strange dibaryon masses, we find that the predicted masses of potential dibaryon states are all in the range from 1900 MeV to 3700 MeV.
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| 4. |
- Blennow, Mattias, 1980-, et al.
(författare)
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A combined study of source, detector and matter non-standard neutrino interactions at DUNE
- 2016
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2016:8
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Tidskriftsartikel (refereegranskat)abstract
- We simultaneously investigate source, detector and matter non-standard neutrino interactions at the proposed DUNE experiment. Our analysis is performed using a Markov Chain Monte Carlo exploring the full parameter space. We find that the sensitivity of DUNE to the standard oscillation parameters is worsened due to the presence of non-standard neutrino interactions. In particular, there are degenerate solutions in the leptonic mixing angle θ23 and the Dirac CP-violating phase δ. We also compute the expected sensitivities at DUNE to the non-standard interaction parameters. We find that the sensitivities to the matter non-standard interaction parameters are substantially stronger than the current bounds (up to a factor of about 15). Furthermore, we discuss correlations between the source/detector and matter non-standard interaction parameters and find a degenerate solution in θ23. Finally, we explore the effect of statistics on our results.
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| 5. |
- Blennow, Mattias, 1980-, et al.
(författare)
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Probing lepton flavor models at future neutrino experiments
- 2020
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 102:11
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Tidskriftsartikel (refereegranskat)abstract
- Non-Abelian discrete symmetries provide an interesting opportunity to address the flavor puzzle in the lepton sector. However, the number of currently viable models based on such symmetries is rather large. High-precision measurements of the leptonic mixing parameters by future neutrino experiments, including ESSnuSB, T2HK, DUNE, and JUNO, will be crucial to test such models. We show that the complementarity among these experiments offers a powerful tool for narrowing down this broad class of lepton flavor models.
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| 6. |
- Blennow, Mattias, 1980-, et al.
(författare)
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Testing lepton flavor models at ESSnuSB
- 2020
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- We review and investigate lepton flavor models, stemming from discrete non- Abelian flavor symmetries, described by one or two free model parameters. First, we confront eleven one- and seven two-parameter models with current results on leptonic mixing angles from global fits to neutrino oscillation data. We find that five of the one- and five of the two-parameter models survive the confrontation test at 3 sigma. Second, we investigate how these ten one- and two-parameter lepton flavor models may be discriminated at the proposed ESSnuSB experiment in Sweden. We show that the three one-parameter models that predict sin delta(CP) = 0 can be distinguished from those two that predict vertical bar sin delta(CP)vertical bar = 1 by at least 7 sigma. Finally, we find that three of the five one-parameter models can be excluded by at least 5 sigma and two of the one-parameter as well as at most two of the five two-parameter models can be excluded by at least 3 sigma with ESSnuSB if the true values of the leptonic mixing parameters remain close to the present best-fit values.
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| 7. |
- Burgman, A., et al.
(författare)
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The ESSnuSB Design Study: Overview and Future Prospects
- 2023
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Ingår i: Universe. - : MDPI. - 2218-1997. ; 9:8
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Forskningsöversikt (refereegranskat)abstract
- ESSnuSB is a design study for an experiment to measure the CP violation in the leptonic sector at the second neutrino oscillation maximum using a neutrino beam driven by the uniquely powerful ESS linear accelerator. The reduced impact of systematic errors on sensitivity at the second maximum allows for a very precise measurement of the CP violating parameter. This review describes the fundamental advantages of measurement at the second maximum, the necessary upgrades to the ESS linac in order to produce a neutrino beam, the near and far detector complexes, and the expected physics reach of the proposed ESSnuSB experiment, concluding with the near future developments aimed at the project realization.
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| 8. |
- Burgman, A., et al.
(författare)
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The European Spallation Source neutrino super-beam conceptual design report
- 2022
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Ingår i: The European Physical Journal Special Topics. - : Springer Nature. - 1951-6355 .- 1951-6401. ; 231:21, s. 3779-3955
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Forskningsöversikt (refereegranskat)abstract
- A design study, named ESSνSB for European Spallation Source neutrino Super Beam, has been carried out during the years 2018–2022 of how the 5 MW proton linear accelerator of the European Spallation Source under construction in Lund, Sweden, can be used to produce the world’s most intense long-baseline neutrino beam. The high beam intensity will allow for measuring the neutrino oscillations near the second oscillation maximum at which the CP violation signal is close to three times higher than at the first maximum, where other experiments measure. This will enable CP violation discovery in the leptonic sector for a wider range of values of the CP violating phase δCPδCP and, in particular, a higher precision measurement of δCPδCP. The present Conceptual Design Report describes the results of the design study of the required upgrade of the ESS linac, of the accumulator ring used to compress the linac pulses from 2.86 ms to 1.2 μs, and of the target station, where the 5 MW proton beam is used to produce the intense neutrino beam. It also presents the design of the near detector, which is used to monitor the neutrino beam as well as to measure neutrino cross sections, and of the large underground far detector located 360 km from ESS, where the magnitude of the oscillation appearance of νe from νμ is measured. The physics performance of the ESSνSB research facility has been evaluated demonstrating that after 10 years of data-taking, leptonic CP violation can be detected with more than 5 standard deviation significance over 70% of the range of values that the CP violation phase angle δCPδCP can take and that δCPδCP can be measured with a standard error less than 8° irrespective of the measured value of δCPδCP. These results demonstrate the uniquely high physics performance of the proposed ESSνSBESSνSB research facility.
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| 9. |
- Burgman, A., et al.
(författare)
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Updated physics performance of the ESSnuSB experiment
- 2021
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Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 81:12
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the physics performance of the ESSnuSB experiment in the standard three flavor scenario using the updated neutrino flux calculated specifically for the ESSnuSB configuration and updated migration matrices for the far detector. Taking conservative systematic uncertainties corresponding to a normalization error of 5% for signal and 10% for background, we find that there is 10 sigma (13 sigma) CP violation discovery sensitivity for the baseline option of 540 km (360 km) at delta(CP) = +/- 90 degrees. The corresponding fraction of delta(CP )for which CP violation can be discovered at more than 5 sigma is 70%. Regarding CP precision measurements, the 1 sigma error associated with delta(CP )= 0 degrees is around 5 degrees and with delta(CP )= -90 degrees is around 14 degrees (7 degrees) for the baseline option of 540 km (360 km). For hierarchy sensitivity, one can have 3 sigma sensitivity for 540 km baseline except delta(CP) = +/- 90 degrees and 5 sigma sensitivity for 360 km baseline for all values of delta(CP). The octant of theta(23) can be determined at 30 for the values of: theta(23) > 51 degrees (theta(23) < 42 degrees and theta(23) > 49 degrees) for baseline of 540 km (360 km). Regarding measurement precision of the atmospheric mixing parameters, the allowed values at 3 sigma are: 40 degrees < theta(23) < 52 degrees (42 degrees < theta(23) < 51.5 degrees) and 2.485 x 10(-3) eV(2) < Delta(2)(m31) < 2.545 x 10(-3) eV(2) (2.49x 10(-3 ) eV(2) < Delta(2)(m31) < 2.54 x 10(-3) eV(2)) for the baseline of 540 km (360 km).
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| 10. |
- Choubey, Sandhya, et al.
(författare)
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Exploring invisible neutrino decay at ESSnuSB
- 2021
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2021:5
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Tidskriftsartikel (refereegranskat)abstract
- We explore invisible neutrino decay in which a heavy active neutrino state decays into a light sterile neutrino state and present a comparative analysis of two baseline options, 540 km and 360 km, for the ESSnuSB experimental setup. Our analysis shows that ESSnuSB can put a bound on the decay parameter τ3/m3 = 2.64 (1.68) × 10−11 s/eV for the baseline option of 360 (540) km at 3σ. The expected bound obtained for 360 km is slightly better than the corresponding one of DUNE for a charged current (CC) analysis. Furthermore, we show that the capability of ESSnuSB to discover decay, and to measure the decay parameter precisely, is better for the baseline option of 540 km than that of 360 km. Regarding effects of decay in δCP measurements, we find that in general the CP violation discovery potential is better in the presence of decay. The change in CP precision is significant if one assumes decay in data but no decay in theory.
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| 11. |
- Ghosh, Manojit, et al.
(författare)
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A comparative study between ESSnuSB and T2HK in determining the leptonic CP phase
- 2020
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Ingår i: Modern Physics Letters A. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 0217-7323 .- 1793-6632. ; 35:5
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we perform a comparative analysis between the future proposed longbaseline experiments ESSnuSB and T2HK in measuring the leptonic CP phase delta(CP). In particular, we study the effect of the neutrino mass ordering degeneracy and the leptonic mixing angle theta(23) octant degeneracy in the measurement of leptonic CP violation and precision for both experiments. Since the ESSnuSB (T2HK) experiment probes the second (first) oscillation maximum to study neutrino oscillations, the effect of these degeneracies are significantly different in both experiments. Our main conclusion is that for the ESSnuSB experiment, the information on the neutrino mass ordering does not play a major role in the determination of delta(CP), which is not the case for the T2HK experiment. However, the information on the true octant compromises the CP sensitivity of the ESSnuSB experiment as compared to T2HK if theta(23) lies in the lower octant. These conclusions are true for both the 540 km and 360 km baseline options for the ESSnuSB experiment. In addition, we investigate the effect of different running times in neutrino and antineutrino modes and the effect of theta(23) precision in measuring delta(CP).
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| 12. |
- Ghosh, Manojit, et al.
(författare)
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Sensitivity to light sterile neutrinos at ESSnuSB
- 2020
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Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :3
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive analysis in the 3+1 active-sterile neutrino oscillation scenario for the sensitivity of the ESSnuSB experiment in the presence of light sterile neutrinos assuming both a far (FD) and a near (ND) detector. Our analysis show that when the ND is included, the results are significantly different compared to the ones obtained with the FD only. We find that the capability of ESSnuSB to constrain the sterile mixing parameters is sin(2) 2 theta(mu e)similar to 10(-4) for m(2) = 1 eV(2) if the ND is included and it becomes sin(2) 2 theta(mu e)similar to 10(-2) without the ND. Furthermore, we show that the sensitivity can go down to sin(2) 2 theta(mu e)similar to 10(-3) for the most conservative choice of the systematics on the ND. Comparing the sensitivity with T2HK, T2HKK, and DUNE by considering the FD only, we find that the sensitivity of ESSnuSB is smaller for most of the parameter space. Studying the CP violation sensitivity, we find that if the ND is included, it can be larger in the 3+1 scenario than in the standard one. However, if the ND is not included, the sensitivity is smaller compared to the one in the standard scenario. We also find that the CP violation sensitivity due to delta(13) is larger compared to the one induced by delta(24). The sensitivities are slightly better for the dominant neutrino running ratio of ESSnuSB.
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| 13. |
- Herrero-Garcia, Juan, et al.
(författare)
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Full parameter scan of the Zee model : exploring Higgs lepton flavor violation
- 2017
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :4
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Tidskriftsartikel (refereegranskat)abstract
- We study the general Zee model, which includes an extra Higgs scalar doublet and a new singly-charged scalar singlet. Neutrino masses are generated at one-loop level, and in order to describe leptonic mixing, both the Standard Model and the extra Higgs scalar doublets need to couple to leptons (in a type-III two-Higgs doublet model), which necessarily generates large lepton flavor violating signals, also in Higgs decays. Imposing all relevant phenomenological constraints and performing a full numerical scan of the parameter space, we find that both normal and inverted neutrino mass orderings can be fitted, although the latter is disfavored with respect to the former. In fact, inverted ordering can only be accommodated if theta(23) turns out to be in the first octant. A branching ratio for h -> tau mu of up to 10(-2) is allowed, but it could be as low as 10(-6). In addition, if future expected sensitivities of tau -> mu gamma are achieved, normal ordering can be almost completely tested. Also, mu e conversion is expected to probe large parts of the parameter space, excluding completely inverted ordering if no signal is observed. Furthermore, non-standard neutrino interactions are found to be smaller than 10(-6), which is well below future experimental sensitivity. Finally, the results of our scan indicate that the masses of the additional scalars have to be below 2.5 TeV, and typically they are lower than that and therefore within the reach of the LHC and future colliders.
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| 14. |
- Holma, Pontus, et al.
(författare)
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Phenomenological predictions for pentaquark masses from fits to baryon masses
- 2020
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Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 800
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mass spectra of exotic hadrons known as pentaquarks. We extend a simple phenomenological model based on the Gursey-Radicati mass formula for hadrons to include both charmed and bottom baryons as well as to be able to predict masses of pentaquark states including both charm and bottom quark-antiquark pairs. In particular, we perform numerical fits of this model, which includes seven free parameters, to masses of 21 baryons. We find that the model can be well fitted to the experimental values of the baryon masses and observe that the predicted value of about 4400 MeV for the mass of the pentaquark P-c(4380)(+) lies within the experimental range reported by the LHCb experiment. In addition, the predicted value of about 4500 MeV for the mass of the pentaquark P-c(4450)(+) is close to the experimental value. Finally, in the future, other predicted values for masses of additional pentaquarks could be shown to agree with upcoming experimental results.
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| 15. |
- Kuhnel, Florian, et al.
(författare)
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Primordial Black-Hole Signatures in Neutrino Telescopes
- 2019
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Ingår i: Probing Particle Physics With Neutrino Telescopes. - : World Scientific Pub Co Pte Ltd. ; , s. 401-418
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The class of scenarios in which sterile neutrinos are constituents of the dark matter also includes those where the latter contains additionally other objects. If these are primordial black holes, halos of sterile neutrinos may form around those. Also in the case that large density fluctuations enter the Hubble horizon at an early time, so-called ultracompact mini-halos of sterile neutrinos may form. Both of these cases can lead to observable signatures through neutrino and photon emission from the mentioned localized objects. In this chapter, it is demonstrated that there exists a broad range of possible parameter choices such that detection in the near future with X-ray and gamma-ray telescopes might be possible. In fact, for energies above 10TeV, kilometer-cube neutrino telescopes can be excellent detection machines for such macroscopic dark matter candidates.
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| 16. |
- Lundhammar, Per, et al.
(författare)
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Nonrelativistic model of tetraquarks and predictions for their masses from fits to charmed and bottom meson data
- 2020
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Ingår i: Physical Review D. - : American Physical Society (APS). - 1550-7998 .- 1550-2368. ; 102:5
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate a nonrelativistic model of tetraquarks, which are assumed to be compact and to consist of diquark-antidiquark pairs. We fit, for the first time, basically all currently known values for the measured masses of 45 mesons, including both charmed and bottom mesons, to the model and predict masses of tetraquarks as well as diquarks. In particular, we find masses of four axial-vector diquarks, i.e., qc, cc, qb, and bb, where q = u, d, and 24 ground-state tetraquarks, including both heavy-light tetraquarks (qc (qc) over bar and qb (qb) over bar) and heavy tetraquarks (cc (cc) over bar and bb (bb) over bar). In general, our results for the masses of qb (qb) over bar, cc (cc) over bar, and bb (bb) over bar are largely comparable with other reported results, whereas our results for the masses of qc (qc) over bar are slightly larger than what has been found earlier. Finally, we identify some of the obtained predictions for masses of tetraquarks with masses of experimental tetraquark candidates, and especially, we find that psi(4660), Z(b)(10610), and Z(b)(10650) could be described by the model.
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| 17. |
- Meloni, Davide, et al.
(författare)
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Threshold effects in SO(10) models with one intermediate breaking scale
- 2020
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Ingår i: European Physical Journal C. - : SPRINGER. - 1434-6044 .- 1434-6052. ; 80:9
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the successes of the Standard Model of particle physics, it is known to suffer from a number of deficiencies. Several of these can be addressed within non-supersymmetric theories of grand unification based on SO(10). However, achieving gauge coupling unification in such theories is known to require additional physics below the unification scale, such as symmetry breaking in multiple steps. Many such models are disfavored due to bounds on the proton lifetime. Corrections arising from threshold effects can, however, modify these conclusions. We analyze all seven relevant breaking chains with one intermediate symmetry breaking scale, assuming the "survival hypothesis" for the scalar masses. Two are allowed by proton lifetime and two are disfavored by a failure to unify the gauge couplings. The remaining three unify at a too low scale, but can be salvaged by various amounts of threshold corrections. We parametrize this and thereby rank the models by the size of the threshold corrections required to save them.
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| 18. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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Density-matrix formalism for PT-symmetric non-Hermitian Hamiltonians with the Lindblad equation
- 2021
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of Lindblad decoherence, i.e., dissipative effects in an open quantum system due to interaction with an environment, we examine the transition probabilities between the eigenstates in the two-level quantum system described by non-Hermitian Hamiltonians with the Lindblad equation, for which the parity-time-reversal (PT) symmetry is conserved. First, the density matrix formalism for PT-symmetric non-Hermitian Hamiltonian systems is developed. It is shown that the Lindblad operators L-j are pseudo-Hermitian, namely, eta L-j eta(-1) = L-j(up arrow) with eta being a linear and positive-definite metric, and respect the PT symmetry as well. We demonstrate that the generalized density matrix rho(G)(t) rho(t )eta, instead of the normalized density matrix rho(N)(t) rho(t )/tr[rho(t)], should be implemented for the calculation of the transition probabilities in accordance with the linearity requirement. Second, the density matrix formalism is used to derive the transition probabilities in general cases of PT-symmetric non-Hermitian Hamiltonians. In some concrete examples, we calculate compact analytical formulas for the transition probabilities and explore their main features with numerical illustrations. We also make a comparison between our present results and our previous ones using state vectors in the absence of Lindblad decoherence.
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| 19. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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Flavor symmetries in the Yukawa sector of non-supersymmetric SO(10) : numerical fits using renormalization group running
- 2021
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :9
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a class of SO(10) models with flavor symmetries in the Yukawa sector and investigate their viability by performing numerical fits to the fermion masses and mixing parameters. The fitting procedure involves a top-down approach in which we solve the renormalization group equations from the scale of grand unification down to the electroweak scale. This allows the intermediate scale right-handed neutrinos and scalar triplet, involved in the type I and II seesaw mechanisms, to be integrated out at their corresponding mass scales, leading to a correct renormalization group running. The result is that, of the 14 models considered, only two are able to fit the known data well. Both these two models correspond to Z(2) symmetries. In addition to being able to fit the fermion masses and mixing parameters, they provide predictions for the sum of light neutrino masses and the effective neutrinoless double beta decay mass parameter, which are both within current observational bounds.
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| 20. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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One-loop matching conditions in neutrino effective theory
- 2022
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Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213 .- 1873-1562. ; 978
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate matching conditions and threshold corrections between full and effective theories based on the type I seesaw mechanism. In general, using an intuitive Feynman diagrammatical approach, we compute the amplitudes before and after integrating out heavy right-handed neutrinos at the matching scale. In particular, we derive the one-loop matching conditions between the full and the effective theories. The matching conditions of the parameters are influenced by one-loop corrections to the corresponding vertices as well as wave function corrections for the Higgs and the lepton fields. Our results are comparable to earlier results based on a functional approach.
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| 21. |
- Ohlsson, Tommy, Professor, 1973-
(författare)
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Proton decay
- 2023
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Ingår i: Nuclear Physics B. - : Elsevier BV. - 0550-3213 .- 1873-1562. ; 993
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Forskningsöversikt (refereegranskat)abstract
- Proton decay is a hypothetical form of particle decay in which protons are assumed to decay into lighter particles. This form of decay has yet to be detected. In this contribution to the proceedings of Neutrino 2022, we review the current status of proton decay, covering both experimental results and theoretical models, including their predictions.
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| 22. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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Realizing unification in two different SO(10) models with one intermediate breaking scale
- 2020
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media Deutschland GmbH. - 1434-6044 .- 1434-6052. ; 80:11
-
Tidskriftsartikel (refereegranskat)abstract
- We derive the threshold corrections in SO (10) grand unified models with the intermediate symmetry being flipped SU(5)×U(1) or SU(3)×SU(2)×U(1)×U(1), with the masses of the scalar fields set by the survival hypothesis. These models do not achieve gauge coupling unification if the matching conditions do not take threshold corrections into account. We present results showing the required size of threshold corrections for any value of the intermediate and unification scales. In particular, our results demonstrate that both of these models are disfavored since they require large threshold corrections to allow for unification with a predicted proton lifetime above current experimental bounds.
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| 23. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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Transition probabilities for flavor eigenstates of non-Hermitian Hamiltonians in the PT-broken phase
- 2021
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Ingår i: Journal of Mathematical Physics. - : AIP Publishing. - 0022-2488 .- 1089-7658. ; 62:4
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the transition probabilities for the "flavor" eigenstates in the two-level quantum system, which is described by a non-Hermitian Hamiltonian with the parity and time-reversal (PT) symmetry. Particularly, we concentrate on the so-called PT-broken phase, where two eigenvalues of the non-Hermitian Hamiltonian turn out to be a complex-conjugate pair. In this case, we find that the transition probabilities will be unbounded in the limit of infinite time t -> +infinity. However, after performing a connection between a non-Hermitian system, which exhibits passive PT symmetry and global decay, and the neutral-meson system in particle physics, we observe that the diverging behavior of the transition probabilities is actually applicable to the gauge-transformed neutral-meson states, whereas the transition probabilities for physical states are exponentially suppressed by the global decay. We also present a brief review on the situation at the so-called exceptional point, where both the eigenvalues and eigenvectors of the Hamiltonian coalesce.
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| 24. |
- Ohlsson, Tommy, Professor, 1973-, et al.
(författare)
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Transition probabilities in the two-level quantum system with PT-symmetric non-Hermitian Hamiltonians
- 2020
-
Ingår i: Journal of Mathematical Physics. - : AIP Publishing. - 0022-2488 .- 1089-7658. ; 61:5
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate how to define in a consistent way the probabilities of the transitions between the "flavor" states of the two-level quantum system, which is described by a non-Hermitian but parity and time-reversal (PT) symmetric Hamiltonian. Explicit calculations are carried out to demonstrate the conservation of probability if a proper definition of the final state is adopted. Finally, this formalism is applied to two-flavor neutrino oscillations nu(mu) -> nu(mu) and nu(mu) -> nu(tau) in vacuum, where the exact PT symmetry requires the vacuum mixing angle to be maximal, which is compatible with current neutrino oscillation experiments. A possible generalization to the three-flavor case is briefly discussed.
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| 25. |
- Pernow, Marcus
(författare)
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Phenomenology of SO(10) Grand Unified Theories
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the Standard Model (SM) of particle physics describes observations well, there are several shortcomings of it. The most crucial of these are that the SM cannot explain the origin of neutrino masses and the existence of dark matter. Furthermore, there are several aspects of it that are seemingly ad hoc, such as the choice of gauge group and the cancellation of gauge anomalies.These shortcomings point to a theory beyond the SM. Although there are many proposed models for physics beyond the SM, in this thesis, we focus on grand unified theories based on the SO(10) gauge group. It predicts that the three gauge groups in the SM unify at a higher energy into one, which contains the SM as a subgroup. We focus on the Yukawa sector of these models and investigate the extent to which the observables such as fermion masses and mixing parameters can be accommodated into different models based on the SO(10) gauge group. Neutrino masses and leptonic mixing parameters are particularly interesting, since SO(10) models naturally embed the seesaw mechanism.The difference in energy scale between the electroweak scale and the scale of unification spans around 14 orders of magnitude. Therefore, one must relate the parameters of the SO(10) model to those of the SM through renormalization group equations. We investigate this for several different models by performing fits of SO(10) models to fermion masses and mixing parameters, taking into account thresholds at which heavy right-handed neutrinos are integrated out of the theory. Although the results are in general dependent on the particular model under consideration, there are some general results that appear to hold true. The observ- ables of the Yukawa sector can in general be accommodated into SO(10) models only if the neutrino masses are normally ordered and that inverted ordering is strongly disfavored. We find that the observable that provides the most tension in the fits is the leptonic mixing angle θ2l3, whose value is consistently favored to be lower in the fits than the actual value. Furthermore, we find that numerical fits to the data favor type-I seesaw over type-II seesaw for the generation of neutrino masses.
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