## _wp09137 - References..........................................33

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### Main result and mechanism
- Limited asset-market participation (a fraction 1¡λ of “assetholders” and fraction λ of “non-assetholders” who consume current income each period) creates a role for active fiscal stabilization that is absent under full asset-market participation.
- Intuition:
  - Monetary policy mainly contracts asset-holder consumption and, via wages and labor supply, stabilizes inflation.
  - Government expenditure raises non-assetholders’ consumption and reduces asset-holders’ consumption, producing a favourable redistribution of stabilization burdens across groups when λ>0.
  - With limited asset-market participation, distributional considerations make expansionary fiscal policy (higher government expenditure) optimal alongside tighter monetary policy.

### Calibration and key parameters (baseline)
- Quarterly discount factor: β = 0.99 (annual steady-state interest ≈ 4 percent).
- Elasticity of substitution: ε = 6 (consistent with 20 percent steady-state markup).
- Labour supply parameter: η = 1 (unit labour supply elasticity).
- Calvo price stickiness: θ = 0.75 (average period of one year between price adjustments).
- Steady-state consumption-to-output ratio: α = 0.75.
- Share of non-assetholders (baseline): λ = 0.4; threshold for “non‑Keynesian” region: λ̄ = 0.58.
- Cost-push shock specification: persistence ρ = 0.75; standard deviation = 0.005.

### Determinacy properties
- With endogenous government expenditure responding to inflation, the Taylor principle remains a sufficient condition for determinacy when λ < λ̄, except when the fiscal response to inflation (ψσπ) is very large and positive; then monetary policy must respond more aggressively to secure determinacy.
- “Non‑Keynesian” region: when λ > λ̄ = 1/(1+ηα) = 0.58 in the calibration, higher real interest rates can raise aggregate demand, reversing conventional policy effects; determinacy then requires violating the Taylor principle (see Appendix E).

### Social welfare and loss function
- Social welfare is utilitarian: weighted sum of asset- and non-assetholders’ utilities with weights determined by λ.
- Second-order expected discounted loss (up to omitted policy-independent terms) is:
  - 1/2 E_t Σ σ= t β^{σ−t} [ ε·β·π_σ^2 + (η+λ)/(1−λ) · ψ-term · y_σ^2 + (1−α) g_σ^2 + α(1−λ) c_O,σ^2 + α λ c_R,σ^2 ], as detailed in equation (22).
- Distributional volatility of private consumption across agent types enters welfare directly: volatility of c_O and c_R matters separately.

### Optimal monetary policy with exogenous fiscal policy
- Optimal current-inflation instrument rule (white-noise cost-push shocks, ρ = 0 case) is:
  - r_t = φ_x^π · π_t with φ_x^π = ε(1+αη)η / (αε£) (where £ = 1−λ + α(η + λ(1+αη^2)) > 0).
- Key qualitative results:
  - The optimal responsiveness of the nominal interest rate to inflation, φ_x^π, falls with the share of non-assetholders λ (∂φ_x^π/∂λ < 0).
  - Under limited asset-market participation, the consumption of non-assetholders contracts more than asset-holders in response to a monetary tightening; this distributional cost reduces optimal monetary tightening relative to the full-participation case.
  - The Taylor principle continues to hold under optimal monetary policy provided λ is not too large (λ < ^λ, expression given in text).

### Jointly optimal monetary and fiscal policy (discretionary)
- With proportional profit taxes financing government expenditure and logarithmic utility baseline:
  - Optimal instrument rules (white-noise cost-push shocks) can be expressed as:
    - r_t = φ_o^π · π_t
    - g_t = ψ_o^π · π_t
  - Closed-form expressions: φ_o^π and ψ_o^π are given in Section IV.C (symbolic structure preserved).
- Main findings:
  - With full asset-market participation (λ = 0), optimal fiscal policy is inactive (ψ_o^π = 0) and monetary policy alone implements stabilization.
  - With λ > 0, the optimal policy raises both the real interest rate and government expenditure in response to a positive cost-push shock: contractionary monetary policy combined with expansionary fiscal policy.
    - Rationale: expansionary government expenditure stabilizes non-assetholders’ consumption and labor supply (reducing the uneven distribution of welfare losses); monetary tightening offsets the inflationary effect of higher government spending.
  - The optimal monetary tightening under joint optimization is larger than under exogenous fiscal policy (φ_o^π − φ_x^π > 0), enabling determinacy for a larger range of λ.
  - The optimal fiscal response ψ_o^π and the additional monetary tightening both rise with λ (∂ψ_o^π/∂λ > 0 and ∂(φ_o^π − φ_x^π)/∂λ > 0).

### Welfare gains of optimising fiscal policy
- Active fiscal policy (optimizing g_t jointly with r_t) raises welfare relative to the case with exogenous government spending, especially for more persistent shocks (Figure 4 highlights welfare gains for ρ = 0, 0.5, 0.75).
- For the baseline calibration (λ = 0.4, ρ = 0.75) the availability of targeted transfers (see below) raises welfare by 0.35 percent of steady-state consumption.

### Robustness and extensions
1. CRRA preferences (generalising from logarithmic utility)
   - Period utility: U_{φ,σ} = C_{φ,σ}^{1−σ}/(1−σ) + Ψ G_{σ}^{1−σ}/(1−σ) − N_{φ,σ}^{1+η}/(1+η), with σ the inverse IES.
   - Main effects:
     - Non-assetholders’ labor supply ν_R is no longer constant; both groups’ labor responses matter.
     - Qualitative baseline result persists: optimal fiscal policy remains active (Figure 5 cross-line), though the magnitude of the fiscal response is moderated when ν_R adjusts.
2. Targeted lump-sum transfers to non-assetholders
   - If the policymaker can implement a time-varying, targeted lump-sum transfer Λ_R,t (financed by lump-sum tax on assetholders), the optimal policy is:
     - r_t = ε/α · π_t
     - g_t = 0
     - Λ_R,t = ε(1+η) · π_t
   - Result: the optimal policy replicates the full asset-market participation case; active government expenditure is no longer used when transfers are available (Figure 5 dashed line).
   - Practical note: targeted transfers require time-varying lump-sum instruments and identification of asset vs non-asset households.
3. Alternative financing: equal lump-sum tax on both agents
   - When government expenditure is financed by equal lump-sum taxes on both groups (instead of profit taxes), the policymaker can use g_t to mimic targeted transfers by cutting public expenditure and rebating resources to consumers.
   - Simulation (Figure 5 dotted line): optimal fiscal response can be negative (government expenditure reduced) to replicate targeted transfer outcomes via untargeted lump-sum taxes.
4. Government debt financing
   - Introducing one-period nominal government debt with linearised law of motion (equation (40)) and steady-state debt ratio B matters for determinacy and optimal fiscal response.
   - Calibration comparison: low-debt economy B = 0 versus high-debt B = 0.2.
   - Findings:
     - Determinacy depends on both monetary response to inflation and fiscal response to debt.
     - For low steady-state debt, optimal fiscal policy still initially raises government expenditure and then reduces it to control debt (dashed line in Figure 6).
     - For higher steady-state debt, the optimal response to a positive cost-push shock can switch to a reduction in government expenditure because higher debt accumulation makes expanding government spending infeasible under discretionary policies (dotted line in Figure 6).
     - This reversal is specific to discretionary policy; commitment policies need not return debt to pre-shock levels and may continue to expand government expenditure even with high B.

### Non‑Keynesian region (brief)
- When λ is “too high” (λ > λ̄ = 0.58 in the baseline calibration), the effects of interest rates and fiscal policy can be inverted: increases in real interest rates and cuts in government expenditure can raise aggregate demand. Determinacy in this region typically requires violating the Taylor principle (see Appendix E).
- The main qualitative result — that optimal fiscal policy raises government expenditure in response to higher inflation — continues to hold in the non‑Keynesian region, though the optimal monetary response differs (optimal policy reduces the real interest rate in that region under certain specifications).

### Policy implications and caveats
- Active fiscal stabilization (expansionary government expenditure) can be welfare-improving when a non-trivial share of consumers cannot smooth consumption through asset markets because fiscal policy redistributes stabilization costs toward those agents most affected by nominal rigidities.
- The beneficial role of fiscal policy relies on the central bank’s ability to offset the inflationary consequences of fiscal expansion by raising the policy rate; constraints (e.g., fixed exchange rate or binding zero lower bound) can eliminate this channel.
- Availability of targeted lump-sum transfers or untargeted lump-sum taxes operating as transfers greatly reduces or eliminates the need for active government expenditure as a stabilization tool.
- High steady-state government debt can reverse the result: under discretionary policy and high B, optimal fiscal policy may cut government expenditure following cost-push shocks because of indebtedness and return-to-pre-shock debt constraints.

*Source: _wp09137 - References..........................................33*

### References..........................................33

### _wp09137 - References..........................................33

### Main result and mechanism
- Limited asset-market participation (a fraction 1¡λ of “assetholders” and fraction λ of “non-assetholders” who consume current income each period) creates a role for active fiscal stabilization that is absent under full asset-market participation.
- Intuition:
  - Monetary policy mainly contracts asset-holder consumption and, via wages and labor supply, stabilizes inflation.
  - Government expenditure raises non-assetholders’ consumption and reduces asset-holders’ consumption, producing a favourable redistribution of stabilization burdens across groups when λ>0.
  - With limited asset-market participation, distributional considerations make expansionary fiscal policy (higher government expenditure) optimal alongside tighter monetary policy.

### Calibration and key parameters (baseline)
- Quarterly discount factor: β = 0.99 (annual steady-state interest ≈ 4 percent).
- Elasticity of substitution: ε = 6 (consistent with 20 percent steady-state markup).
- Labour supply parameter: η = 1 (unit labour supply elasticity).
- Calvo price stickiness: θ = 0.75 (average period of one year between price adjustments).
- Steady-state consumption-to-output ratio: α = 0.75.
- Share of non-assetholders (baseline): λ = 0.4; threshold for “non‑Keynesian” region: λ̄ = 0.58.
- Cost-push shock specification: persistence ρ = 0.75; standard deviation = 0.005.

### Determinacy properties
- With endogenous government expenditure responding to inflation, the Taylor principle remains a sufficient condition for determinacy when λ < λ̄, except when the fiscal response to inflation (ψσπ) is very large and positive; then monetary policy must respond more aggressively to secure determinacy.
- “Non‑Keynesian” region: when λ > λ̄ = 1/(1+ηα) = 0.58 in the calibration, higher real interest rates can raise aggregate demand, reversing conventional policy effects; determinacy then requires violating the Taylor principle (see Appendix E).

### Social welfare and loss function
- Social welfare is utilitarian: weighted sum of asset- and non-assetholders’ utilities with weights determined by λ.
- Second-order expected discounted loss (up to omitted policy-independent terms) is:
  - 1/2 E_t Σ σ= t β^{σ−t} [ ε·β·π_σ^2 + (η+λ)/(1−λ) · ψ-term · y_σ^2 + (1−α) g_σ^2 + α(1−λ) c_O,σ^2 + α λ c_R,σ^2 ], as detailed in equation (22). (Preserve the structure and coefficients as in the source.)
- Distributional volatility of private consumption across agent types enters welfare directly: volatility of c_O and c_R matters separately.

### Optimal monetary policy with exogenous fiscal policy
- Optimal current-inflation instrument rule (white-noise cost-push shocks, ρ = 0 case) is:
  - r_t = φ_x^π · π_t with φ_x^π = ε(1+αη)η / (αε£) (where £ = 1−λ + α(η + λ(1+αη^2)) > 0). (Form preserved as in text.)
- Key qualitative results:
  - The optimal responsiveness of the nominal interest rate to inflation, φ_x^π, falls with the share of non-assetholders λ (∂φ_x^π/∂λ < 0).
  - Under limited asset-market participation, the consumption of non-assetholders contracts more than asset-holders in response to a monetary tightening; this distributional cost reduces optimal monetary tightening relative to the full-participation case.
  - The Taylor principle continues to hold under optimal monetary policy provided λ is not too large (λ < ^λ, expression given in text).

### Jointly optimal monetary and fiscal policy (discretionary)
- With proportional profit taxes financing government expenditure and logarithmic utility baseline:
  - Optimal instrument rules (white-noise cost-push shocks) can be expressed as:
    - r_t = φ_o^π · π_t
    - g_t = ψ_o^π · π_t
  - Closed-form expressions: φ_o^π and ψ_o^π are given in Section IV.C (preserved symbolic structure in the source).
- Main findings:
  - With full asset-market participation (λ = 0), optimal fiscal policy is inactive (ψ_o^π = 0) and monetary policy alone implements stabilization (standard result).
  - With λ > 0, the optimal policy raises both the real interest rate and government expenditure in response to a positive cost-push shock: contractionary monetary policy combined with expansionary fiscal policy.
    - Rationale: expansionary government expenditure stabilizes non-assetholders’ consumption and labor supply (reducing the uneven distribution of welfare losses); monetary tightening offsets the inflationary effect of higher government spending.
  - The optimal monetary tightening under joint optimization is larger than under exogenous fiscal policy (φ_o^π − φ_x^π > 0), enabling determinacy for a larger range of λ.
  - The optimal fiscal response ψ_o^π and the additional monetary tightening both rise with λ (∂ψ_o^π/∂λ > 0 and ∂(φ_o^π − φ_x^π)/∂λ > 0).

### Welfare gains of optimising fiscal policy
- Active fiscal policy (optimizing g_t jointly with r_t) raises welfare relative to the case with exogenous government spending, especially for more persistent shocks (Figure 4 highlights welfare gains for ρ = 0, 0.5, 0.75).
- For the baseline calibration (λ = 0.4, ρ = 0.75) the availability of targeted transfers (see below) raises welfare by 0.35 percent of steady-state consumption.

### Robustness and extensions
1. CRRA preferences (generalising from logarithmic utility)
   - Period utility: U_{φ,σ} = C_{φ,σ}^{1−σ}/(1−σ) + Ψ G_{σ}^{1−σ}/(1−σ) − N_{φ,σ}^{1+η}/(1+η), with σ the inverse IES.
   - Main effects:
     - Non-assetholders’ labor supply ν_R is no longer constant; both groups’ labor responses matter.
     - Qualitative baseline result persists: optimal fiscal policy remains active (Figure 5 cross-line), though the magnitude of the fiscal response is moderated when ν_R adjusts.
2. Targeted lump-sum transfers to non-assetholders
   - If the policymaker can implement a time-varying, targeted lump-sum transfer Λ_R,t (financed by lump-sum tax on assetholders), the optimal policy is:
     - r_t = ε/α · π_t
     - g_t = 0
     - Λ_R,t = ε(1+η) · π_t
   - Result: the optimal policy replicates the full asset-market participation case; active government expenditure is no longer used when transfers are available (Figure 5 dashed line).
   - Practical note: targeted transfers require time-varying lump-sum instruments and identification of asset vs non-asset households.
3. Alternative financing: equal lump-sum tax on both agents
   - When government expenditure is financed by equal lump-sum taxes on both groups (instead of profit taxes), the policymaker can use g_t to mimic targeted transfers by cutting public expenditure and rebating resources to consumers.
   - Simulation (Figure 5 dotted line): optimal fiscal response can be negative (government expenditure reduced) to replicate targeted transfer outcomes via untargeted lump-sum taxes.
4. Government debt financing
   - Introducing one-period nominal government debt with linearised law of motion (equation (40)) and steady-state debt ratio B matters for determinacy and optimal fiscal response.
   - Calibration comparison: low-debt economy B = 0 versus high-debt B = 0.2.
   - Findings:
     - Determinacy depends on both monetary response to inflation and fiscal response to debt.
     - For low steady-state debt, optimal fiscal policy still initially raises government expenditure and then reduces it to control debt (dashed line in Figure 6).
     - For higher steady-state debt, the optimal response to a positive cost-push shock can switch to a reduction in government expenditure because higher debt accumulation makes expanding government spending infeasible under discretionary policies (dotted line in Figure 6).
     - This reversal is specific to discretionary policy; commitment policies need not return debt to pre-shock levels and may continue to expand government expenditure even with high B.

### Non‑Keynesian region (brief)
- When λ is “too high” (λ > λ̄ = 0.58 in the baseline calibration), the effects of interest rates and fiscal policy can be inverted: increases in real interest rates and cuts in government expenditure can raise aggregate demand. Determinacy in this region typically requires violating the Taylor principle (see Appendix E).
- The main qualitative result — that optimal fiscal policy raises government expenditure in response to higher inflation — continues to hold in the non‑Keynesian region, though the optimal monetary response differs (optimal policy reduces the real interest rate in that region under certain specifications).

### Policy implications and caveats
- Active fiscal stabilization (expansionary government expenditure) can be welfare-improving when a non-trivial share of consumers cannot smooth consumption through asset markets because fiscal policy redistributes stabilization costs toward those agents most affected by nominal rigidities.
- The beneficial role of fiscal policy relies on the central bank’s ability to offset the inflationary consequences of fiscal expansion by raising the policy rate; constraints (e.g., fixed exchange rate or binding zero lower bound) can eliminate this channel.
- Availability of targeted lump-sum transfers or untargeted lump-sum taxes operating as transfers greatly reduces or eliminates the need for active government expenditure as a stabilization tool.
- High steady-state government debt can reverse the result: under discretionary policy and high B, optimal fiscal policy may cut government expenditure following cost-push shocks because of indebtedness and return-to-pre-shock debt constraints.

*Source: _wp09137 - References..........................................33*

### References

### References

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*Source: _wp09137 - References*

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_Source: https://www.imf.org/-/media/websites/imf/imported-full-text-pdf/external/pubs/ft/wp/2009/_wp09137.pdf_
